outer space

The use of the short version space, as meaning "the region beyond Earth's sky", predates the use of full term "outer space", with the earliest recorded use of this meaning in an epic poem by John Milton called Paradise Lost, published in 1667.

The term outward space existed in a poem from 1842 by the English poet Lady Emmeline Stuart-Wortley called "The Maiden of Moscow",{{sfn|Stuart Wortley|1841|p=410}} but in astronomy the term outer space found its application for the first time in 1845 by Alexander von Humboldt.{{sfn|Von Humboldt|1845|p=39}} The term was eventually popularized through the writings of H. G. Wells after 1901. Theodore von Kármán used the term of free space to name the space of altitudes above Earth where spacecrafts reach conditions sufficiently free from atmospheric drag, differentiating it from airspace, identifying a legal space above territories free from the sovereign jurisdiction of countries.

"Spaceborne" denotes existing in outer space, especially if carried by a spacecraft; similarly, "space-based" means based in outer space or on a planet or moon.

{{Main|Big Bang}}

File:CMB Timeline300 no WMAP.jpg, where visible space is represented by the circular sections. At left, a dramatic expansion occurs in the inflationary epoch, and at the center, the expansion accelerates. Neither time nor size are to scale.]]

The size of the whole universe is unknown, and it might be infinite in extent.{{sfn|Liddle|2015|pp=33}} According to the Big Bang theory, the very early universe was an extremely hot and dense state about 13.8 billion years ago which rapidly expanded. About 380,000 years later the universe had cooled sufficiently to allow protons and electrons to combine and form hydrogen—the so-called recombination epoch. When this happened, matter and energy became decoupled, allowing photons to travel freely through the continually expanding space. Matter that remained following the initial expansion has since undergone gravitational collapse to create stars, galaxies and other astronomical objects, leaving behind a deep vacuum that forms what is now called outer space.{{sfn|Silk|2000|pp=105–308}} As light has a finite velocity, this theory constrains the size of the directly observable universe.

The present day shape of the universe has been determined from measurements of the cosmic microwave background using satellites like the Wilkinson Microwave Anisotropy Probe. These observations indicate that the spatial geometry of the observable universe is "flat", meaning that photons on parallel paths at one point remain parallel as they travel through space to the limit of the observable universe, except for local gravity. The flat universe, combined with the measured mass density of the universe and the accelerating expansion of the universe, indicates that space has a non-zero vacuum energy, which is called dark energy.{{sfn|Sparke|Gallagher|2007|pp=329–330}}

Estimates put the average energy density of the present day universe at the equivalent of 5.9 protons per cubic meter, including dark energy, dark matter, and baryonic matter (ordinary matter composed of atoms). The atoms account for only 4.6% of the total energy density, or a density of one proton per four cubic meters. The density of the universe is clearly not uniform; it ranges from relatively high density in galaxies—including very high density in structures within galaxies, such as planets, stars, and black holes—to conditions in vast voids that have much lower density, at least in terms of visible matter. Unlike matter and dark matter, dark energy seems not to be concentrated in galaxies: although dark energy may account for a majority of the mass-energy in the universe, dark energy's influence is 5 orders of magnitude smaller than the influence of gravity from matter and dark matter within the Milky Way.

{{Main|Space environment|Space weather|Space weathering}}

File:Night Sky from Hawai‘i and Chile (iotw2225c).jpg is visible as the horizontal band of zodiacal light, including the false dawn (edges) and gegenschein (center), which is visually crossed by the Milky Way]]

Outer space is the closest known approximation to a perfect vacuum. It has effectively no friction, allowing stars, planets, and moons to move freely along their orbits. The deep vacuum of intergalactic space is not devoid of matter, as it contains a few hydrogen atoms per cubic meter. By comparison, the air humans breathe contains about 10²⁵ molecules per cubic meter.{{sfn|Borowitz|Beiser|1971}} The low density of matter in outer space means that electromagnetic radiation can travel great distances without being scattered: the mean free path of a photon in intergalactic space is about 10²³ km, or 10 billion light years.{{sfn|Davies|1977|p=93}} In spite of this, extinction, which is the absorption and scattering of photons by dust and gas, is an important factor in galactic and intergalactic astronomy.

Stars, planets, and moons retain their atmospheres by gravitational attraction. Atmospheres have no clearly delineated upper boundary: the density of atmospheric gas gradually decreases with distance from the object until it becomes indistinguishable from outer space.{{sfn|Chamberlain|1978|p=2}} The Earth's atmospheric pressure drops to about {{nowrap|0.032 Pa}} at {{Convert|100|km|mi|abbr=off}} of altitude, compared to 100,000 Pa for the International Union of Pure and Applied Chemistry (IUPAC) definition of standard pressure. Above this altitude, isotropic gas pressure rapidly becomes insignificant when compared to radiation pressure from the Sun and the dynamic pressure of the solar wind. The thermosphere in this range has large gradients of pressure, temperature and composition, and varies greatly due to space weather.

The temperature of outer space is measured in terms of the kinetic activity of the gas, as it is on Earth. The radiation of outer space has a different temperature than the kinetic temperature of the gas, meaning that the gas and radiation are not in thermodynamic equilibrium.{{sfn|Prialnik|2000|pp=195–196}}{{sfn|Spitzer|1978|p=28–30}} All of the observable universe is filled with photons that were created during the Big Bang, which is known as the cosmic microwave background radiation (CMB). (There is quite likely a correspondingly large number of neutrinos called the cosmic neutrino background.) The current black body temperature of the background radiation is about {{convert|2.7|K|C F|0}}. The gas temperatures in outer space can vary widely. For example, the temperature in the Boomerang Nebula is {{convert|1|K|C F|0}}, while the solar corona reaches temperatures over {{convert|1,200,000|-|2,600,000|K|F|-5}}.

Magnetic fields have been detected in the space around many classes of celestial objects. Star formation in spiral galaxies can generate small-scale dynamos, creating turbulent magnetic field strengths of around 5–10 μG. The Davis–Greenstein effect causes elongated dust grains to align themselves with a galaxy's magnetic field, resulting in weak optical polarization. This has been used to show ordered magnetic fields that exist in several nearby galaxies. Magneto-hydrodynamic processes in active elliptical galaxies produce their characteristic jets and radio lobes. Non-thermal radio sources have been detected even among the most distant high-z sources, indicating the presence of magnetic fields.

Outside a protective atmosphere and magnetic field, there are few obstacles to the passage through space of energetic subatomic particles known as cosmic rays. These particles have energies ranging from about 10⁶ eV up to an extreme 10²⁰ eV of ultra-high-energy cosmic rays. The peak flux of cosmic rays occurs at energies of about 10⁹ eV, with approximately 87% protons, 12% helium nuclei and 1% heavier nuclei. In the high energy range, the flux of electrons is only about 1% of that of protons.{{sfn|Lang|1999|p=462}} Cosmic rays can damage electronic components and pose a health threat to space travelers.{{sfn|Lide|1993|p=11{{hyphen}}217}}

Scents retained from low Earth orbit, when returning from extravehicular activity, have a burned, metallic odor, similar to the scent of arc welding fumes. This results from oxygen in low Earth orbit, which clings to suits and equipment. Other regions of space could have very different odors, like that of different alcohols in molecular clouds.

{{main|Effect of spaceflight on the human body|Space medicine|Bioastronautics}}

{{See also|Astrobiology|Astrobotany|Plants in space|Animals in space}}

File:Bruce McCandless II during EVA in 1984.jpg while outside their spacecraft.|alt=The lower half shows a blue planet with patchy white clouds. The upper half has a man in a white spacesuit and maneuvering unit against a black background.]]

Despite the harsh environment, several life forms have been found that can withstand extreme space conditions for extended periods. Species of lichen carried on the ESA BIOPAN facility survived exposure for ten days in 2007. Seeds of Arabidopsis thaliana and Nicotiana tabacum germinated after being exposed to space for 1.5 years. A strain of Bacillus subtilis has survived 559 days when exposed to low Earth orbit or a simulated Martian environment. The lithopanspermia hypothesis suggests that rocks ejected into outer space from life-harboring planets may successfully transport life forms to another habitable world. A conjecture is that just such a scenario occurred early in the history of the Solar System, with potentially microorganism-bearing rocks being exchanged between Venus, Earth, and Mars.

{{main|Uncontrolled decompression}}

The lack of pressure in space is the most immediate dangerous characteristic of space to humans. Pressure decreases above Earth, reaching a level at an altitude of around {{convert|19.14|km|mi|abbr=on}} that matches the vapor pressure of water at the temperature of the human body. This pressure level is called the Armstrong line, named after American physician Harry G. Armstrong. At or above the Armstrong line, fluids in the throat and lungs boil away. More specifically, exposed bodily liquids such as saliva, tears, and liquids in the lungs boil away. Hence, at this altitude, human survival requires a pressure suit, or a pressurized capsule.{{sfn|Piantadosi|2003|pp=188–189}}

Out in space, sudden exposure of an unprotected human to very low pressure, such as during a rapid decompression, can cause pulmonary barotrauma—a rupture of the lungs, due to the large pressure differential between inside and outside the chest. Even if the subject's airway is fully open, the flow of air through the windpipe may be too slow to prevent the rupture. Rapid decompression can rupture eardrums and sinuses, bruising and blood seep can occur in soft tissues, and shock can cause an increase in oxygen consumption that leads to hypoxia.

As a consequence of rapid decompression, oxygen dissolved in the blood empties into the lungs to try to equalize the partial pressure gradient. Once the deoxygenated blood arrives at the brain, humans lose consciousness after a few seconds and die of hypoxia within minutes. Blood and other body fluids boil when the pressure drops below {{convert|6.3|kPa|psi|0}}, and this condition is called ebullism. The steam may bloat the body to twice its normal size and slow circulation, but tissues are elastic and porous enough to prevent rupture. Ebullism is slowed by the pressure containment of blood vessels, so some blood remains liquid.{{sfn|Billings|1973|pp=1–34}}

Swelling and ebullism can be reduced by containment in a pressure suit. The Crew Altitude Protection Suit (CAPS), a fitted elastic garment designed in the 1960s for astronauts, prevents ebullism at pressures as low as {{convert|2|kPa|psi|1}}. Supplemental oxygen is needed at {{Convert|8|km|mi|0|abbr=on}} to provide enough oxygen for breathing and to prevent water loss, while above {{Convert|20|km|mi|abbr=on}} pressure suits are essential to prevent ebullism.{{sfn|Ellery|2000|p=68}} Most space suits use around {{convert|30|-|39|kPa|psi|0}} of pure oxygen, about the same as the partial pressure of oxygen at the Earth's surface. This pressure is high enough to prevent ebullism, but evaporation of nitrogen dissolved in the blood could still cause decompression sickness and gas embolisms if not managed.{{sfn|Davis|Johnson|Stepanek|2008|pp=270–271}}

{{Main|Weightlessness|Radiobiology}}

Humans evolved for life in Earth gravity, and exposure to weightlessness has been shown to have deleterious effects on human health. Initially, more than 50% of astronauts experience space motion sickness. This can cause nausea and vomiting, vertigo, headaches, lethargy, and overall malaise. The duration of space sickness varies, but it typically lasts for 1–3 days, after which the body adjusts to the new environment. Longer-term exposure to weightlessness results in muscle atrophy and deterioration of the skeleton, or spaceflight osteopenia. These effects can be minimized through a regimen of exercise.{{sfn|Kanas|Manzey|2008|pp=15–48}} Other effects include fluid redistribution, slowing of the cardiovascular system, decreased production of red blood cells, balance disorders, and a weakening of the immune system. Lesser symptoms include loss of body mass, nasal congestion, sleep disturbance, and puffiness of the face.

During long-duration space travel, radiation can pose an acute health hazard. Exposure to high-energy, ionizing cosmic rays can result in fatigue, nausea, vomiting, as well as damage to the immune system and changes to the white blood cell count. Over longer durations, symptoms include an increased risk of cancer, plus damage to the eyes, nervous system, lungs and the gastrointestinal tract. On a round-trip Mars mission lasting three years, a large fraction of the cells in an astronaut's body would be traversed and potentially damaged by high energy nuclei. The energy of such particles is significantly diminished by the shielding provided by the walls of a spacecraft and can be further diminished by water containers and other barriers. The impact of the cosmic rays upon the shielding produces additional radiation that can affect the crew. Further research is needed to assess the radiation hazards and determine suitable countermeasures.

{{For|the furthest reaches of space|observable universe}}

File:Earth's atmosphere.svg

The transition between Earth's atmosphere and outer space lacks a well-defined physical boundary, with the air pressure steadily decreasing with altitude until it mixes with the solar wind. Various definitions for a practical boundary have been proposed, ranging from {{Convert|30|km|mi|abbr=on}} out to {{Convert|1600000|km|mi|abbr=on}}. In 2009, measurements of the direction and speed of ions in the atmosphere were made from a sounding rocket. The altitude of {{Convert|118|km|mi|sigfig=3|abbr=on}} above Earth was the midpoint for charged particles transitioning from the gentle winds of the Earth's atmosphere to the more extreme flows of outer space. The latter can reach velocities well over {{Convert|268|m/s|ft/s|abbr=on}}.

High-altitude aircraft, such as high-altitude balloons have reached altitudes above Earth of up to 50 km. Up until 2021, the United States designated people who travel above an altitude of {{convert|50|mi|km|abbr=on}} as astronauts.{{sfn|Wong|Fergusson|2010|p=16}} Astronaut wings are now only awarded to spacecraft crew members that "demonstrated activities during flight that were essential to public safety, or contributed to human space flight safety".

The region between airspace and outer space is termed "near space". There is no legal definition for this extent, but typically this is the altitude range from {{cvt|20|to|100|km|mi}}. For safety reasons, commercial aircraft are typically limited to altitudes of {{Cvt|12|km|mi}}, and air navigation services only extend to {{cvt|18|to|20|km|mi}}.{{citation | postscript=.

| title=Regulating Near-Space Activities: Using the Precedent of the Exclusive Economic Zone as a Model?

| first1=Hao | last1=Liu | first2=Fabio | last2=Tronchetti

| work=Ocean Development & International Law | year=2019

| doi=10.1080/00908320.2018.1548452 }} The upper limit of the range is the Kármán line, where astrodynamics must take over from aerodynamics in order to achieve flight. This range includes the stratosphere, mesosphere and lower thermosphere layers of the Earth's atmosphere.{{citation | postscript=.

| title=Spatial and Temporal Characterization of Near Space Temperature and Humidity and Their Driving Influences

| last1=Luo | first1=Wenhui | last2=Ma | first2=Jinji

| last3=Li | first3=Miao | last4=Xu | first4=Haifeng

| last5=Wan | first5=Cheng | last6=Li | first6=Zhengqiang

| display-authors=1 | journal=Remote Sensing

| volume=16 | issue=22 | page=4307 | date=November 19, 2024

| issn=2072-4292 | doi=10.3390/rs16224307 | doi-access=free| bibcode=2024RemS...16.4307L

}}

Larger ranges for near space are used by some authors, such as {{cvt|18|to|160|km|mi}}. These extend to the altitudes where orbital flight in very low Earth orbits becomes practical. Spacecraft have entered into a highly elliptical orbit with a perigee as low as {{Convert|80|to|90|km|mi|abbr=on}}, surviving for multiple orbits. At an altitude of {{Convert|120|km|mi|abbr=on}}, descending spacecraft begin atmospheric entry as atmospheric drag becomes noticeable. For spaceplanes such as NASA's Space Shuttle, this begins the process of switching from steering with thrusters to maneuvering with aerodynamic control surfaces.

The Kármán line, established by the Fédération Aéronautique Internationale, and used internationally by the United Nations, is set at an altitude of {{convert|100|km|mi|abbr=on}} as a working definition for the boundary between aeronautics and astronautics. This line is named after Theodore von Kármán, who argued for an altitude where a vehicle would have to travel faster than orbital velocity to derive sufficient aerodynamic lift from the atmosphere to support itself,{{sfn|O'Leary|2009|p=84}} which he calculated to be at an altitude of about {{Convert|83.8|km|mi|abbr=on}}. This distinguishes altitudes below as the region of aerodynamics and airspace, and above as the space of astronautics and free space.

There is no internationally recognized legal altitude limit on national airspace, although the Kármán line is the most frequently used for this purpose. Objections have been made to setting this limit too high, as it could inhibit space activities due to concerns about airspace violations. It has been argued for setting no specified singular altitude in international law, instead applying different limits depending on the case, in particular based on the craft and its purpose. Increased commercial and military sub-orbital spaceflight has raised the issue of where to apply laws of airspace and outer space. Spacecraft have flown over foreign countries as low as {{Convert|30|km|mi|abbr=on}}, as in the example of the Space Shuttle.

{{Main|Space law}}

File:SM-3 launch to destroy the NRO-L 21 satellite.jpg remain legal under the law of armed conflict, even though they create hazardous space debris]]

The Outer Space Treaty provides the basic framework for international space law. It covers the legal use of outer space by nation states, and includes in its definition of outer space, the Moon, and other celestial bodies. The treaty states that outer space is free for all nation states to explore and is not subject to claims of national sovereignty, calling outer space the "province of all mankind". This status as a common heritage of mankind has been used, though not without opposition, to enforce the right to access and shared use of outer space for all nations equally, particularly non-spacefaring nations. It prohibits the deployment of nuclear weapons in outer space. The treaty was passed by the United Nations General Assembly in 1963 and signed in 1967 by the Union of Soviet Socialist Republics (USSR), the United States of America (USA), and the United Kingdom (UK). As of 2017, 105 state parties have either ratified or acceded to the treaty. An additional 25 states signed the treaty, without ratifying it.

Since 1958, outer space has been the subject of multiple United Nations resolutions. Of these, more than 50 have been concerning the international co-operation in the peaceful uses of outer space and preventing an arms race in space. Four additional space law treaties have been negotiated and drafted by the UN's Committee on the Peaceful Uses of Outer Space. Still, there remains no legal prohibition against deploying conventional weapons in space, and anti-satellite weapons have been successfully tested by the USA, USSR, China,{{sfn|Wong|Fergusson|2010|p=4}} and in 2019, India. The 1979 Moon Treaty turned the jurisdiction of all heavenly bodies (including the orbits around such bodies) over to the international community. The treaty has not been ratified by any nation that currently practices human spaceflight.

In 1976, eight equatorial states (Ecuador, Colombia, Brazil, The Republic of the Congo, Zaire, Uganda, Kenya, and Indonesia) met in Bogotá, Colombia: with their "Declaration of the First Meeting of Equatorial Countries", or the Bogotá Declaration, they claimed control of the segment of the geosynchronous orbital path corresponding to each country. These claims are not internationally accepted.

An increasing issue of international space law and regulation has been the dangers of the growing number of space debris.

{{main|Geocentric orbit|Orbital decay}}

File:Newton Cannon.svg, an illustration of how objects can "fall" in a curve around the planet]]

When a rocket is launched to achieve orbit, its thrust must both counter gravity and accelerate it to orbital speed. After the rocket terminates its thrust, it follows an arc-like trajectory back toward the ground under the influence of the Earth's gravitational force. In a closed orbit, this arc will turn into an elliptical loop around the planet. That is, a spacecraft successfully enters Earth orbit when its acceleration due to gravity pulls the craft down just enough to prevent its momentum from carrying it off into outer space.

For a low Earth orbit, orbital speed is about {{Convert|7.8|km/s |mph|-2|abbr=on}}; by contrast, the fastest piloted airplane speed ever achieved (excluding speeds achieved by deorbiting spacecraft) was {{Convert|2.2|km/s|mph|-2|abbr=on}} in 1967 by the North American X-15. At the upper limit of orbital speed at {{Convert|11.2|km/s|mph|-2|abbr=on}} is the velocity required to pull free from Earth altogether and enter into a basic heliocentric orbit. The energy required to reach Earth orbital speed at an altitude of {{Convert|600|km|mi|abbr=on}} is about 36 MJ/kg, which is six times the energy needed merely to climb to the corresponding altitude.

Very low Earth orbit (VLEO) has been defined as orbits that have a mean altitude below 450 km (280 mi), which can be better suited for Earth observation with small satellites. Low Earth orbits in general range in altitude from {{cvt|180|to|2000|km|mi}} and are used for scientific satellites. Medium Earth orbits extends from {{cvt|2000|to|35780|km|mi}}, which are favorable orbits for navigation and specialized satellites. Above {{cvt|35780|km|mi}} are the high Earth orbits used for weather and some communication satellites.

Spacecraft in orbit with a perigee below about {{Convert|2000|km|mi|abbr=on}} (low Earth orbit) are subject to drag from the Earth's atmosphere,{{sfn|Ghosh|2000|pp=47–48}} which decreases the orbital altitude. The rate of orbital decay depends on the satellite's cross-sectional area and mass, as well as variations in the air density of the upper atmosphere, which is significantly effected by space weather. At altitudes above {{cvt|800|km|mi|abbr=on}}, orbital lifetime is measured in centuries. Below about {{cvt|300|km|mi|abbr=on}}, decay becomes more rapid with lifetimes measured in days. Once a satellite descends to {{cvt|180|km|mi|abbr=on}}, it has only hours before it vaporizes in the atmosphere.

Radiation in orbit around Earth is concentrated in Van Allen radiation belts, which trap solar and galactic radiation. Radiation is a threat to astronauts and space systems. It is difficult to shield against and space weather makes the radiation environment variable. The radiation belts are equatorial toroidal regions, which are bent towards Earth's poles, with the South Atlantic Anomaly being the region where charged particles approach Earth closest. The innermost radiaion belt, the inner Van Allen belt, has its intensity peak at altitudes above the equator of half an Earth radius, centered at about 3000 km, increasing from the upper edge of low Earth orbit which it overlaps.

{{Also|Location of Earth}}

The outermost layer of the Earth's atmosphere is termed the exosphere. It extends outward from the thermopause, which lies at an altitude that varies from {{convert|250|to|500|km|mi}}, depending on the incidence of solar radiation. Beyond this altitude, collisions between molecules are negligible and the atmosphere joins with interplanetary space. The region in proximity to the Earth is home to a multitude of Earth–orbiting satellites and has been subject to extensive studies. For identification purposes, this volume is divided into overlapping regions of space.{{sfn|Schrijver|Siscoe|2010|p=363, 379}}

{{Visible anchor|Near-Earth space}} is the region of space extending from low Earth orbits out to geostationary orbits. This region includes the major orbits for artificial satellites and is the site of most of humanity's space activity. The region has seen high levels of space debris, sometimes dubbed space pollution, threatening nearby space activity. Some of this debris re-enters Earth's atmosphere periodically. Although it meets the definition of outer space, the atmospheric density inside low-Earth orbital space, the first few hundred kilometers above the Kármán line, is still sufficient to produce significant drag on satellites.

File:Debris-GEO1280.jpg

{{anchor|Geospace}}Geospace is a region of space that includes Earth's upper atmosphere and magnetosphere.{{sfn|Schrijver|Siscoe|2010|p=363, 379}} The Van Allen radiation belts lie within the geospace. The outer boundary of geospace is the magnetopause, which forms an interface between the Earth's magnetosphere and the solar wind. The inner boundary is the ionosphere.{{sfn|Schrijver|Siscoe|2010|p=379}}

The variable space-weather conditions of geospace are affected by the behavior of the Sun and the solar wind; the subject of geospace is interlinked with heliophysics—the study of the Sun and its impact on the planets of the Solar System.{{sfn|Fichtner|Liu|2011|pp=341–345}} The day-side magnetopause is compressed by solar-wind pressure—the subsolar distance from the center of the Earth is typically 10 Earth radii. On the night side, the solar wind stretches the magnetosphere to form a magnetotail that sometimes extends out to more than 100–200 Earth radii.{{sfn|Koskinen|2010|pp=32, 42}} For roughly four days of each month, the lunar surface is shielded from the solar wind as the Moon passes through the magnetotail.{{sfn|Mendillo|2000|p=275}}

Geospace is populated by electrically charged particles at very low densities, the motions of which are controlled by the Earth's magnetic field. These plasmas form a medium from which storm-like disturbances powered by the solar wind can drive electrical currents into the Earth's upper atmosphere. Geomagnetic storms can disturb two regions of geospace, the radiation belts and the ionosphere. These storms increase fluxes of energetic electrons that can permanently damage satellite electronics, interfering with shortwave radio communication and GPS location and timing.{{sfn|Goodman|2006|p=244}} Magnetic storms can be a hazard to astronauts, even in low Earth orbit. They create aurorae seen at high latitudes in an oval surrounding the geomagnetic poles.

File:Artemis 1 at maximum distance from Earth.jpg mission]]

XGEO space is a concept used by the USA to refer to the space of high Earth orbits, with the 'X' being some multiple of geosynchronous orbit (GEO) at approximately {{convert|35786|km|mi|0|abbr=on}}. Hence, the L2 Earth-Moon Lagrange point at {{convert|448900|km|mi|0|abbr=on}} is approximately 10.67 XGEO. Translunar space is the region of lunar transfer orbits, between the Moon and Earth. {{anchor|Cislunar space}}{{anchor|cislunar space}} Cislunar space is a region outside of Earth that includes lunar orbits, the Moon's orbital space around Earth and the Earth-Moon Lagrange points.

The region where a body's gravitational potential remains dominant against gravitational potentials from other bodies, is the body's sphere of influence or gravity well, mostly described with the Hill sphere model. In the case of Earth this includes all space from the Earth to a distance of roughly 1% of the mean distance from Earth to the Sun,{{sfn|Barbieri|2006|p=253}} or {{convert|1.5|e6km|e6mi|abbr=unit}}. Beyond Earth's Hill sphere extends along Earth's orbital path its orbital and co-orbital space. This space is co-populated by groups of co-orbital Near-Earth Objects (NEOs), such as horseshoe librators and Earth trojans, with some NEOs at times becoming temporary satellites and quasi-moons to Earth.

{{anchor|Deep space}}

Deep space is defined by the United States government as all of outer space which lies further from Earth than a typical low-Earth-orbit, thus assigning the Moon to deep-space. Other definitions vary the starting point of deep-space from, "That which lies beyond the orbit of the moon," to "That which lies beyond the farthest reaches of the Solar System itself."{{sfn|Dickson|2010|p=57}}{{sfn|Williamson|2006|p=97}} The International Telecommunication Union responsible for radio communication, including with satellites, defines deep-space as, "distances from the Earth equal to, or greater than, {{convert|2|e6km|e6mi|abbr=unit}}," which is about five times the Moon's orbital distance, but which distance is also far less than the distance between Earth and any adjacent planet.

File:Orbitalaltitudes.svg

{{main|Interplanetary medium}}

File:Comet Hale-Bopp 1995O1.jpg are being shaped by pressure from solar radiation and the solar wind, respectively.|alt=At lower left, a white coma stands out against a black background. Nebulous material streams away to the top and left, slowly fading with distance.]]

Interplanetary space within the Solar System is the space dominated by the gravitation of the Sun, outside the gravitational spheres of influence of the planets. Interplanetary space extends well beyond the orbit of the outermost planet Neptune, all the way out to where the influence of the galactic environment starts to dominate over the Sun and its solar wind producing the heliopause at 110 to 160 AU. The heliopause deflects away low-energy galactic cosmic rays, and its distance and strength varies depending on the activity level of the solar wind. The solar wind is a continuous stream of charged particles emanating from the Sun which creates a very tenuous atmosphere (the heliosphere) for billions of kilometers into space. This wind has a particle density of 5–10 protons/cm³ and is moving at a velocity of {{Convert|350|-|400|km/s|mph|abbr=on}}.{{sfn|Papagiannis|1972|pp=12–149}}

The region of interplanetary space is a nearly total vacuum, with a mean free path of about one astronomical unit at the orbital distance of the Earth. This space is not completely empty, but is sparsely filled with cosmic rays, which include ionized atomic nuclei and various subatomic particles. There is gas, plasma and dust, small meteors, and several dozen types of organic molecules discovered to date by microwave spectroscopy. Collectively, this matter is termed the interplanetary medium. A cloud of interplanetary dust is visible at night as a faint band called the zodiacal light.

Interplanetary space contains the magnetic field generated by the Sun.{{sfn|Papagiannis|1972|pp=12–149}} There are magnetospheres generated by planets such as Jupiter, Saturn, Mercury and the Earth that have their own magnetic fields. These are shaped by the influence of the solar wind into the approximation of a teardrop shape, with the long tail extending outward behind the planet. These magnetic fields can trap particles from the solar wind and other sources, creating belts of charged particles such as the Van Allen radiation belts. Planets without magnetic fields, such as Mars, have their atmospheres gradually eroded by the solar wind.

{{Redirect|Interstellar space|the album|Interstellar Space}}

{{Main|Interstellar medium}}

File:52706main hstorion lg.jpg formed by the magnetosphere of the young star LL Orionis (center) as it collides with the Orion Nebula flow|alt=Patchy orange and blue nebulosity against a black background, with a curved orange arc wrapping around a star at the center.]]

Interstellar space is the physical space outside of the bubbles of plasma known as astrospheres, formed by stellar winds originating from individual stars, or formed by solar wind emanating from the Sun. It is the space between the stars or stellar systems within a nebula or galaxy. Interstellar space contains an interstellar medium of sparse matter and radiation. The boundary between an astrosphere and interstellar space is known as an astropause. For the Sun, the astrosphere and astropause are called the heliosphere and heliopause, respectively.

Approximately 70% of the mass of the interstellar medium consists of lone hydrogen atoms; most of the remainder consists of helium atoms. This is enriched with trace amounts of heavier atoms formed through stellar nucleosynthesis. These atoms are ejected into the interstellar medium by stellar winds or when evolved stars begin to shed their outer envelopes such as during the formation of a planetary nebula. The cataclysmic explosion of a supernova propagates shock waves of stellar ejecta outward, distributing it throughout the interstellar medium, including the heavy elements previously formed within the star's core. The density of matter in the interstellar medium can vary considerably: the average is around 10⁶ particles per m³, but cold molecular clouds can hold 10⁸–10¹² per m³.{{sfn|Prialnik|2000|pp=195–196}}

A number of molecules exist in interstellar space, which can form dust particles as tiny as 0.1 μm.{{sfn|Rauchfuss|2008|pp=72–81}} The tally of molecules discovered through radio astronomy is steadily increasing at the rate of about four new species per year. Large regions of higher density matter known as molecular clouds allow chemical reactions to occur, including the formation of organic polyatomic species. Much of this chemistry is driven by collisions. Energetic cosmic rays penetrate the cold, dense clouds and ionize hydrogen and helium, resulting, for example, in the trihydrogen cation. An ionized helium atom can then split relatively abundant carbon monoxide to produce ionized carbon, which in turn can lead to organic chemical reactions.

The local interstellar medium is a region of space within 100 pc of the Sun, which is of interest both for its proximity and for its interaction with the Solar System. This volume nearly coincides with a region of space known as the Local Bubble, which is characterized by a lack of dense, cold clouds. It forms a cavity in the Orion Arm of the Milky Way Galaxy, with dense molecular clouds lying along the borders, such as those in the constellations of Ophiuchus and Taurus. The actual distance to the border of this cavity varies from 60 to 250 pc or more. This volume contains about 10⁴–10⁵ stars and the local interstellar gas counterbalances the astrospheres that surround these stars, with the volume of each sphere varying depending on the local density of the interstellar medium. The Local Bubble contains dozens of warm interstellar clouds with temperatures of up to 7,000 K and radii of 0.5–5 pc.

When stars are moving at sufficiently high peculiar velocities, their astrospheres can generate bow shocks as they collide with the interstellar medium. For decades it was assumed that the Sun had a bow shock. In 2012, data from Interstellar Boundary Explorer (IBEX) and NASA's Voyager probes showed that the Sun's bow shock does not exist. Instead, these authors argue that a subsonic bow wave defines the transition from the solar wind flow to the interstellar medium. A bow shock is a third boundary characteristic of an astrosphere, lying outside the termination shock and the astropause.

{{Main|Warm–hot intergalactic medium|Intracluster medium|Intergalactic dust}}

File:Structure of the Universe.jpgs of the intergalactic medium]]

Intergalactic space is the physical space between galaxies. Studies of the large-scale distribution of galaxies show that the universe has a foam-like structure, with groups and clusters of galaxies lying along filaments that occupy about a tenth of the total space. The remainder forms cosmic voids that are mostly empty of galaxies. Typically, a void spans a distance of 7–30 megaparsecs.{{sfn|Wszolek|2013|p=67}}

Surrounding and stretching between galaxies is the intergalactic medium (IGM). This rarefied plasma is organized in a galactic filamentary structure. The diffuse photoionized gas contains filaments of higher density, about one atom per cubic meter, which is 5–200 times the average density of the universe. The IGM is inferred to be mostly primordial in composition, with 76% hydrogen by mass, and enriched with higher mass elements from high-velocity galactic outflows.

As gas falls into the intergalactic medium from the voids, it heats up to temperatures of 10⁵ K to 10⁷ K. At these temperatures, it is called the warm–hot intergalactic medium (WHIM). Although the plasma is very hot by terrestrial standards, 10⁵ K is often called "warm" in astrophysics. Computer simulations and observations indicate that up to half of the atomic matter in the universe might exist in this warm–hot, rarefied state. When gas falls from the filamentary structures of the WHIM into the galaxy clusters at the intersections of the cosmic filaments, it can heat up even more, reaching temperatures of 10⁸ K and above in the so-called intracluster medium (ICM).

{{multiple image

| perrow = 7

| align = center

| direction = horizontal

| background color =

| width =

| caption_align = center

| header_background =

| header_align = center

| header = Overview of different scales of space as regions around Earth

| image1 = L2 rendering.jpg

| width1 = 93

| caption1 = Earth-Moon System

| image2 = Inner solar system objects top view for wiki.png

| width2 = 93

| caption2 = Inner Solar System with Near-Earth objects

| image3 = Oort cloud Sedna orbit.svg

| width3 = 93

| caption3 = Solar System and Oort cloud

| image4 = Angular map of fusors around Sol within 9ly (large).png

| width4 = 93

| caption4 = Nearest stars

| image5 = Local Interstellar Clouds with motion arrows.jpg

| width5 = 93

| caption5 = Local Interstellar Cloud and neighbouring interstellar medium

| image6 = Galaxymap.com, map 100 parsecs (2022).png

| width6 = 93

| caption6 = Star associations and interstellar medium map of the Local Bubble

| image7 = Galaxymap.com, map 1000 parsecs (2022).png

| width7 = 93

| caption7 = Molecular clouds around the Sun inside the Orion-Cygnus Arm

| image8 = OrionSpur.png

| width8 = 93

| caption8 = Orion-Cygnus Arm and neighbouring arms

| image9 = Milky Way Arms ssc2008-10.svg

| width9 = 93

| caption9 = Orion-Cygnus Arm inside the Milky Way

| image10 = Milky Way side view.png

| width10 = 93

| caption10 = The Sun within the structure of the Milky Way

| image11 = 06-Local Group (LofE06240).png

| width11 = 93

| caption11 = Satellite galaxies of the Milky Way in Local Group

| image12 = 07-Laniakea (LofE07240).png

| width12 = 93

| caption12 = Virgo SCl in Laniakea SCl

| image13 = Laniakea.gif

| width13 = 93

| caption13 = Laniakea SCl in Pisces–Cetus Supercluster Complex

| image14 = Observable Universe with Measurements 01.png

| width14 = 93

| caption14 = Observable Universe of the Universe

| footer_background =

| footer_align = center

| footer =

}}

{{Further|Timeline of knowledge about galaxies, clusters of galaxies, and large-scale structure}}

In 350 BCE, Greek philosopher Aristotle suggested that nature abhors a vacuum, a principle that became known as the horror vacui. This concept built upon a 5th-century BCE ontological argument by the Greek philosopher Parmenides, who denied the possible existence of a void in space.{{sfn|Grant|1981|p=10}} Based on this idea that a vacuum could not exist, in the West it was widely held for many centuries that space could not be empty.{{sfn|Porter|Park|Daston|2006|p=27}} As late as the 17th century, the French philosopher René Descartes argued that the entirety of space must be filled.{{sfn|Eckert|2006|p=5}}

In ancient China, the 2nd-century astronomer Zhang Heng became convinced that space must be infinite, extending well beyond the mechanism that supported the Sun and the stars. The surviving books of the Hsüan Yeh school said that the heavens were boundless, "empty and void of substance". Likewise, the "sun, moon, and the company of stars float in the empty space, moving or standing still".{{sfn|Needham|Ronan|1985|pp=82–87}}

The Italian scientist Galileo Galilei knew that air had mass and so was subject to gravity. In 1640, he demonstrated that an established force resisted the formation of a vacuum. It would remain for his pupil Evangelista Torricelli to create an apparatus that would produce a partial vacuum in 1643. This experiment resulted in the first mercury barometer and created a scientific sensation in Europe. Torricelli suggested that since air has weight, then air pressure should decrease with altitude. The French mathematician Blaise Pascal proposed an experiment to test this hypothesis.{{sfn|Holton|Brush|2001|pp=267–268}} In 1648, his brother-in-law, Florin Périer, repeated the experiment on the Puy de Dôme mountain in central France and found that the column was shorter by three inches. This decrease in pressure was further demonstrated by carrying a half-full balloon up a mountain and watching it gradually expand, then contract upon descent.{{sfn|Cajori|1917|pp=64–66}}

File:Magedurger Halbkugeln Luftpumpe Deutsches Museum.jpg (left) used to demonstrate Otto von Guericke's vacuum pump (right)|alt=A glass display case holds a mechanical device with a lever arm, plus two metal hemispheres attached to draw ropes.]]

In 1650, German scientist Otto von Guericke constructed the first vacuum pump: a device that would further refute the principle of horror vacui. He correctly noted that the atmosphere of the Earth surrounds the planet like a shell, with the density gradually declining with altitude. He concluded that there must be a vacuum between the Earth and the Moon.{{sfn|Genz|2001|pp=127–128}}

In the 15th century, German theologian Nicolaus Cusanus speculated that the universe lacked a center and a circumference. He believed that the universe, while not infinite, could not be held as finite as it lacked any bounds within which it could be contained.{{sfn|Tassoul|Tassoul|2004|p=22}} These ideas led to speculations as to the infinite dimension of space by the Italian philosopher Giordano Bruno in the 16th century. He extended the Copernican heliocentric cosmology to the concept of an infinite universe filled with a substance he called aether, which did not resist the motion of heavenly bodies.{{sfn|Gatti|2002|pp=99–104}} English philosopher William Gilbert arrived at a similar conclusion, arguing that the stars are visible to us only because they are surrounded by a thin aether or a void.{{sfn|Kelly|1965|pp=97–107}} This concept of an aether originated with ancient Greek philosophers, including Aristotle, who conceived of it as the medium through which the heavenly bodies move.{{sfn|Olenick|Apostol|Goodstein|1986|p=356}}

The concept of a universe filled with a luminiferous aether retained support among some scientists until the early 20th century. This form of aether was viewed as the medium through which light could propagate.{{sfn|Hariharan|2003|p=2}} In 1887, the Michelson–Morley experiment tried to detect the Earth's motion through this medium by looking for changes in the speed of light depending on the direction of the planet's motion. The null result indicated something was wrong with the concept. The idea of the luminiferous aether was then abandoned. It was replaced by Albert Einstein's theory of special relativity, which holds that the speed of light in a vacuum is a fixed constant, independent of the observer's motion or frame of reference.{{sfn|Olenick|Apostol|Goodstein|1986|pp=357–365}}{{sfn|Thagard|1992|pp=206–209}}

The first professional astronomer to support the concept of an infinite universe was the Englishman Thomas Digges in 1576.{{sfn|Maor|1991|p=195}} But the scale of the universe remained unknown until the first successful measurement of the distance to a nearby star in 1838 by the German astronomer Friedrich Bessel. He showed that the star system 61 Cygni had a parallax of just 0.31 arcseconds (compared to the modern value of 0.287″). This corresponds to a distance of over 10 light years.{{sfn|Webb|1999|pp=71–73}} In 1917, Heber Curtis noted that novae in spiral nebulae were, on average, 10 magnitudes fainter than galactic novae, suggesting that the former are 100 times further away. The distance to the Andromeda Galaxy was determined in 1923 by American astronomer Edwin Hubble by measuring the brightness of cepheid variables in that galaxy, a new technique discovered by Henrietta Leavitt. This established that the Andromeda Galaxy, and by extension all galaxies, lay well outside the Milky Way.{{sfn|Tyson|Goldsmith|2004|pp=114–115}} With this Hubble formulated the Hubble constant, which allowed for the first time a calculation of the age of the Universe and size of the Observable Universe, starting at 2 billion years and 280 million light-years. This became increasingly precise with better measurements, until 2006 when data of the Hubble Space Telescope allowed a very accurate calculation of the age of the Universe and size of the Observable Universe.

The modern concept of outer space is based on the "Big Bang" cosmology, first proposed in 1931 by the Belgian physicist Georges Lemaître. This theory holds that the universe originated from a state of extreme energy density that has since undergone continuous expansion.

The earliest known estimate of the temperature of outer space was by the Swiss physicist Charles É. Guillaume in 1896. Using the estimated radiation of the background stars, he concluded that space must be heated to a temperature of 5–6 K. British physicist Arthur Eddington made a similar calculation to derive a temperature of 3.18 K in 1926. German physicist Erich Regener used the total measured energy of cosmic rays to estimate an intergalactic temperature of 2.8 K in 1933. American physicists Ralph Alpher and Robert Herman predicted 5 K for the temperature of space in 1948, based on the gradual decrease in background energy following the then-new Big Bang theory.

{{Main|Space exploration|Human presence in space}}

{{See also|Astronautics|Spaceflight|Human spaceflight}}

File:As08-16-2593.jpg taken by a person, probably by Bill Anders (during the 1968 Apollo 8 mission)]]

For most of human history, space was explored by observations made from the Earth's surface—initially with the unaided eye and then with the telescope. Before reliable rocket technology, the closest that humans had come to reaching outer space was through balloon flights. In 1935, the American Explorer II crewed balloon flight reached an altitude of {{Convert|22|km|mi|abbr=on}}. This was greatly exceeded in 1942 when the third launch of the German A-4 rocket climbed to an altitude of about {{Convert|80|km|mi|abbr=on}}. In 1957, the uncrewed satellite Sputnik 1 was launched by a Russian R-7 rocket, achieving Earth orbit at an altitude of {{Convert|215|-|939|km|mi}}.{{sfn|O'Leary|2009|pp=209–224}} This was followed by the first human spaceflight in 1961, when Yuri Gagarin was sent into orbit on Vostok 1. The first humans to escape low Earth orbit were Frank Borman, Jim Lovell and William Anders in 1968 on board the American Apollo 8, which achieved lunar orbit{{sfn|Harrison|2002|pp=60–63}} and reached a maximum distance of {{Convert|377349|km|mi|abbr=on}} from the Earth.{{sfn|Orloff|2001}}

The first spacecraft to reach escape velocity was the Soviet Luna 1, which performed a fly-by of the Moon in 1959.{{sfn|Hardesty|Eisman|Krushchev|2008|pp=89–90}} In 1961, Venera 1 became the first planetary probe. It revealed the presence of the solar wind and performed the first fly-by of Venus, although contact was lost before reaching Venus. The first successful planetary mission was the 1962 fly-by of Venus by Mariner 2.{{sfn|Collins|2007|p=86}} The first fly-by of Mars was by Mariner 4 in 1964. Since that time, uncrewed spacecraft have successfully examined each of the Solar System's planets, as well their moons and many minor planets and comets. They remain a fundamental tool for the exploration of outer space, as well as for observation of the Earth.{{sfn|Harris|2008|pp=7, 68–69}} In August 2012, Voyager 1 became the first man-made object to leave the Solar System and enter interstellar space.

{{See also|Space science|Benefits of space exploration|Earth observation|Commercialization of space|Space habitation}}

File:ISS-44 Milky Way.jpg is an orbiting laboratory for space applications and habitability. Visible in the background is yellow-green airglow of Earth's ionosphere and the interstellar field of the Milky Way.]]

Outer space has become an important element of global society. It provides multiple applications that are beneficial to the economy and scientific research.

The placing of artificial satellites in Earth orbit has produced numerous benefits and has become the dominating sector of the space economy. They allow relay of long-range communications like television, provide a means of precise navigation, and permit direct monitoring of weather conditions and remote sensing of the Earth. The latter role serves a variety of purposes, including tracking soil moisture for agriculture, prediction of water outflow from seasonal snow packs, detection of diseases in plants and trees, and surveillance of military activities.{{sfn|Razani|2012|pp=97–99}} They facilitate the discovery and monitoring of climate change influences. Satellites make use of the significantly reduced drag in space to stay in stable orbits, allowing them to efficiently span the whole globe, compared to for example stratospheric balloons or high-altitude platform stations, which have other benefits.

The absence of air makes outer space an ideal location for astronomy at all wavelengths of the electromagnetic spectrum. This is evidenced by the pictures sent back by the Hubble Space Telescope, allowing light from more than 13 billion years ago—almost to the time of the Big Bang—to be observed. Not every location in space is ideal for a telescope. The interplanetary zodiacal dust emits a diffuse near-infrared radiation that can mask the emission of faint sources such as extrasolar planets. Moving an infrared telescope out past the dust increases its effectiveness. Likewise, a site like the Daedalus crater on the far side of the Moon could shield a radio telescope from the radio frequency interference that hampers Earth-based observations.

File:Solardisk.jpg system to beam energy down to Earth]]

The deep vacuum of space could make it an attractive environment for certain industrial processes, such as those requiring ultraclean surfaces. Like asteroid mining, space manufacturing would require a large financial investment with little prospect of immediate return. An important factor in the total expense is the high cost of placing mass into Earth orbit: ${{Inflation|US|6000|2006|r=-3|fmt=c}}–${{Inflation|US|20000|2006|r=-3|fmt=c}} per kg, according to a 2006 estimate (allowing for inflation since then). The cost of access to space has declined since 2013. Partially reusable rockets such as the Falcon 9 have lowered access to space below 3500 dollars per kilogram. With these new rockets the cost to send materials into space remains prohibitively high for many industries. Proposed concepts for addressing this issue include, fully reusable launch systems, non-rocket spacelaunch, momentum exchange tethers, and space elevators.{{sfn|Bolonkin|2010|p=xv}}

Interstellar travel for a human crew remains at present only a theoretical possibility. The distances to the nearest stars mean it would require new technological developments and the ability to safely sustain crews for journeys lasting several decades. For example, the Daedalus Project study, which proposed a spacecraft powered by the fusion of deuterium and helium-3, would require 36 years to reach the "nearby" Alpha Centauri system. Other proposed interstellar propulsion systems include light sails, ramjets, and beam-powered propulsion. More advanced propulsion systems could use antimatter as a fuel, potentially reaching relativistic velocities.

From the Earth's surface, the ultracold temperature of outer space can be used as a renewable cooling technology for various applications on Earth through passive daytime radiative cooling. This enhances longwave infrared (LWIR) thermal radiation heat transfer through the amosphere's infrared window into outer space, lowering ambient temperatures. Photonic metamaterials can be used to suppress solar heating.

{{div col|colwidth=20em}}

• Absolute space and time
• Artemis Accords
• List of government space agencies
• List of topics in space
• Olbers' paradox
• Outline of space science
• Panspermia
• Space art
• Space and survival
• Space race
• Space station
• Space technology
• Timeline of knowledge about the interstellar and intergalactic medium
• Timeline of Solar System exploration
• Timeline of spaceflight

{{div col end}}

{{Reflist

|refs =

{{citation | postscript=.

| author=Representatives of the States traversed by the Equator

| title = Declaration of the first meeting of equatorial countries

| date=December 3, 1976

| location=Bogota, Republic of Colombia

| work=Space Law | publisher=JAXA

| url = http://www.jaxa.jp/library/space_law/chapter_2/2-2-1-2_e.html | url-status=live

| archive-url=https://web.archive.org/web/20111124065449/http://www.jaxa.jp/library/space_law/chapter_2/2-2-1-2_e.html

| access-date=2011-10-14 | archive-date=November 24, 2011 }}

{{citation | postscript=.

| title=Who Owns the Geostationary Orbit?

| first=Thomas | last=Gangale

| journal=Annals of Air and Space Law

| volume=31 | year=2006

| url=http://pweb.jps.net/~gangale/opsa/ir/WhoOwnsGeostationaryOrbit.htm

| archive-url=https://web.archive.org/web/20110927091830/http://pweb.jps.net/~gangale/opsa/ir/WhoOwnsGeostationaryOrbit.htm

| access-date=2011-10-14 | archive-date=2011-09-27 }}

{{citation | postscript=.

| title=What is the Universe Made Of?

| first=Edward J. | last=Wollack

| publisher=NASA | date=June 24, 2011

| url = http://map.gsfc.nasa.gov/universe/uni_matter.html | url-status=live

| archive-url = https://web.archive.org/web/20160726014944/http://map.gsfc.nasa.gov/universe/uni_matter.html

| access-date=2011-10-14 | archive-date=2016-07-26 }}

{{citation | first=Tom | last=Squire | date=September 27, 2000 | title=U.S. Standard Atmosphere, 1976 | publisher=NASA | work=Thermal Protection Systems Expert and Material Properties Database | url = http://tpsx.arc.nasa.gov/cgi-perl/alt.pl | access-date=2011-10-23 | postscript=. | archive-url = https://web.archive.org/web/20111015062917/http://tpsx.arc.nasa.gov/cgi-perl/alt.pl | archive-date=October 15, 2011 }}

{{citation | postscript=.

| last=Fitzpatrick | first=E. L.

| contribution=Interstellar Extinction in the Milky Way Galaxy

| title=Astrophysics of Dust | series=ASP Conference Series

| editor1-first=Adolf N. | editor1-last=Witt

| editor2-first=Geoffrey C. | editor2-last=Clayton

| editor3-first=Bruce T. | editor3-last=Draine

| volume=309 | page=33 |date=May 2004

| bibcode=2004ASPC..309...33F | arxiv=astro-ph/0401344 }}

{{citation | last=Tadokoro | first=M. | title=A Study of the Local Group by Use of the Virial Theorem | journal=Publications of the Astronomical Society of Japan | volume=20 | page=230 | year=1968 | bibcode=1968PASJ...20..230T | postscript=. }} This source estimates a density of {{nowrap|7 × 10⁻²⁹ g/cm³}} for the Local Group. An atomic mass unit is {{nowrap|1.66 × 10⁻²⁴ g}}, for roughly 40 atoms per cubic meter.

{{citation | display-authors=1 | first1=David | last1=Williams | first2=Andre | last2=Kuipers | first3=Chiaki | last3=Mukai | first4=Robert | last4=Thirsk | title=Acclimation during space flight: effects on human physiology | journal=Canadian Medical Association Journal | date=June 23, 2009 | volume=180 | issue=13 | pages=1317–1323 | doi=10.1503/cmaj.090628 | pmid=19509005 | postscript=. | pmc=2696527 }}

{{citation | postscript=.

| title=Radiation Effects

| first=Ann R. | last=Kennedy

| publisher=National Space Biological Research Institute

| url=http://www.nsbri.org/SCIENCE-and-TECHNOLOGY/Radiation-Effects/ | url-status=live

| archive-url=https://web.archive.org/web/20120103195825/http://www.nsbri.org/SCIENCE-and-TECHNOLOGY/Radiation-Effects/

| access-date=2011-12-16 | archive-date=2012-01-03 }}

{{citation | postscript=.

| title=The hazards of space travel

| first=Richard B. | last=Setlow

| journal=Science and Society

| volume=4 | issue=11 | pages=1013–1016 | date=November 2003

| doi=10.1038/sj.embor.7400016

| pmid=14593437 | pmc=1326386 }}

{{citation

| last1= Curtis | first1=S. B. | last2= Letaw | first2=J. W. | year=1989 | title=Galactic cosmic rays and cell-hit frequencies outside the magnetosphere | journal=Advances in Space Research | pages=293–298 | volume=9 | issue=10 | bibcode=1989AdSpR...9c.293C | doi=10.1016/0273-1177(89)90452-3 | pmid=11537306 }}

{{citation | first1=R. M. | last1=Harding | first2=F. J. | last2=Mills | title=Aviation medicine. Problems of altitude I: hypoxia and hyperventilation | journal=British Medical Journal | volume=286 | issue=6375 | pages=1408–1410 | doi=10.1136/bmj.286.6375.1408 | pmid=6404482 | date=April 30, 1983 | postscript=. | pmc=1547870 }}

{{citation | postscript=.

| title=Acute exposure to altitude

| last=Hodkinson | first=P. D.

| journal=Journal of the Royal Army Medical Corps

| date=March 2011 | volume=157 | issue=1 | pages=85–91

| doi=10.1136/jramc-157-01-15 | s2cid=43248662 | pmid=21465917

| url=http://www.ramcjournal.com/2011/mar11/hodkinson.pdf

| archive-url=https://web.archive.org/web/20120426054930/http://www.ramcjournal.com/2011/mar11/hodkinson.pdf

| archive-date=2012-04-26 |access-date=2011-12-16 }}

{{citation | postscript=.

| title=Index of Online General Assembly Resolutions Relating to Outer Space

| publisher=United Nations Office for Outer Space Affairs

| year=2011

| url=http://www.unoosa.org/oosa/SpaceLaw/gares/index.html | url-status=live

| archive-url=https://web.archive.org/web/20100115120820/http://www.unoosa.org/oosa/SpaceLaw/gares/index.html

| access-date=2009-12-30 | archive-date=2010-01-15 }}

{{citation | postscript=.

| title=Entry | work=Human Spaceflight | publisher=NASA

| first=John Ira | last=Petty | date=February 13, 2003

| url=http://spaceflight.nasa.gov/shuttle/reference/shutref/events/entry/

| archive-url=https://web.archive.org/web/20111027174930/http://spaceflight.nasa.gov/shuttle/reference/shutref/events/entry/

| access-date=2011-12-16

| archive-date=October 27, 2011 }}

{{citation | postscript=.

| title=Edge of Space Found

| first1=Andrea | last1=Thompson

| date=April 9, 2009 | publisher=space.com

| url=http://www.space.com/scienceastronomy/090409-edge-space.html | url-status=live

| archive-url=https://web.archive.org/web/20090714002304/http://www.space.com/scienceastronomy/090409-edge-space.html

| access-date=2009-06-19 | archive-date=July 14, 2009 }}

{{citation | display-authors=1 | first1=L. | last1=Sangalli | first2=D. J. | last2=Knudsen | first3=M. F. | last3=Larsen | first4=T. | last4=Zhan | first5=R. F. | last5=Pfaff | first6=D. | last6=Rowland | year=2009 | title=Rocket-based measurements of ion velocity, neutral wind, and electric field in the collisional transition region of the auroral ionosphere | journal=Journal of Geophysical Research | volume=114 | issue=A4 | pages=A04306 | doi=10.1029/2008JA013757 | bibcode=2009JGRA..114.4306S | postscript=. | doi-access=free }}

{{citation | postscript=.

| title=X-15 Walkaround

| first=Linda | last=Shiner

| date=November 1, 2007

| publisher=Air & Space Magazine

| url=http://www.airspacemag.com/history-of-flight/x-15_walkaround.html

| access-date=2009-06-19 }}

{{citation | postscript=.

| title=Space | date=November 2001

| first=Douglas | last=Harper

| publisher=The Online Etymology Dictionary

| url=http://www.etymonline.com/index.php?term=space | url-status=live

| archive-url=https://web.archive.org/web/20090224134354/http://www.etymonline.com/index.php?term=space

| access-date=2009-06-19 | archive-date=2009-02-24 }}

{{citation | title=The origin of intergalactic magnetic fields due to extragalactic jets |date=July 1992 | last1=Jafelice | first1=Luiz C. | last2=Opher | first2=Reuven | journal=Monthly Notices of the Royal Astronomical Society | volume=257 | issue=1 | pages=135–151 | bibcode=1992MNRAS.257..135J | postscript=. | doi= 10.1093/mnras/257.1.135 | doi-access=free }}

{{citation | display-authors=1 | first1=James W. | last1=Wadsley | first2=Marcelo I. | last2=Ruetalo | first3=J. Richard | last3=Bond | first4=Carlo R. | last4=Contaldi | first5=Hugh M. P. | last5=Couchman | first6=Joachim | last6=Stadel | first7=Thomas R. | last7=Quinn | first8=Michael D. | last8=Gladders | url=http://antwrp.gsfc.nasa.gov/apod/ap020820.html | title=The Universe in Hot Gas | work=Astronomy Picture of the Day | date=August 20, 2002 | publisher=NASA | access-date=2009-06-19 | postscript=. | url-status=live | archive-url=https://web.archive.org/web/20090609150938/http://antwrp.gsfc.nasa.gov/apod/ap020820.html | archive-date=June 9, 2009 }}

{{citation | display-authors=1 | last1=Flynn | first1=G. J. | last2=Keller | first2=L. P. | last3=Jacobsen | first3=C. | last4=Wirick | first4=S. | contribution=The Origin of Organic Matter in the Solar System: Evidence from the Interplanetary Dust Particles | title=Bioastronomy 2002: Life Among the Stars, Proceedings of IAU Symposium No. 213 | volume=213 | page=275 | editor1-first=R. | editor1-last=Norris | editor2-first=F. | editor2-last=Stootman | year=2003 | bibcode=2004IAUS..213..275F | postscript=. }}

{{citation | last1=Johnson | first1=R. E. | title=Plasma-Induced Sputtering of an Atmosphere | journal=Space Science Reviews | volume=69 | issue=3–4 | pages=215–253 |date=August 1994 | doi=10.1007/BF02101697 | bibcode=1994SSRv...69..215J | s2cid=121800711 | postscript=. }}

{{citation | first1=Matthew B. | last1=Krebs | first2=Andrew A. | last2=Pilmanis | date=November 1996 | publisher=United States Air Force Armstrong Laboratory | title=Human pulmonary tolerance to dynamic over-pressure | url=https://apps.dtic.mil/sti/pdfs/ADA318718.pdf | access-date=2011-12-23 | postscript=. | url-status=live | archive-url=https://web.archive.org/web/20121130045759/http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA318718 | archive-date=2012-11-30 }}

{{citation | first1=John | last1=Kennewell | first2=Andrew | last2=McDonald | year=2011 | publisher=Commonwealth of Australia Bureau of Weather, Space Weather Branch | title=Satellite Lifetimes and Solar Activity | url=http://www.ips.gov.au/Educational/1/3/8 | access-date=2011-12-31 | postscript=. | url-status=live | archive-url=https://web.archive.org/web/20111228025141/http://www.ips.gov.au/Educational/1/3/8 | archive-date=2011-12-28 }}

{{citation | postscript=.

| contribution=Astrometric and Geodetic Properties of Earth and the Solar System

| last=Yoder | first=Charles F.

| title=Global earth physics a handbook of physical constants

| editor1-first=Thomas J. | editor1-last=Ahrens

| series=AGU reference shelf Series

| page=1 | year=1995 | volume=1 | isbn=978-0-87590-851-9

| publisher=American Geophysical Union |location=Washington, DC

| bibcode=1995geph.conf....1Y

| url=http://terra.sgt-inc.com/pub/jmccarth/GEODYN_class/class_materials_DVD/references/4_yoder.pdf |access-date=2011-12-31

| archive-url=https://web.archive.org/web/20120426082632/http://terra.sgt-inc.com/pub/jmccarth/GEODYN_class/class_materials_DVD/references/4_yoder.pdf

| archive-date=April 26, 2012

}}. This work lists a Hill sphere radius of 234.9 times the mean radius of Earth, or {{val|234.9|×|6,371|u=km}} = 1.5 million km.

{{citation | last1=Landgraf | first1=M. | last2=Jehn | first2=R. | last3=Flury | first3=W. | last4=Fridlund | first4=M. | last5=Karlsson | first5=A. | last6=Léger | first6=A. | display-authors=1 | title=IRSI/Darwin: peering through the interplanetary dust cloud | journal=ESA Bulletin | volume=105 | issue=105 | pages=60–63 |date=February 2001 | bibcode=2001ESABu.105...60L|arxiv = astro-ph/0103288 | postscript=. }}

{{citation

| contribution=Searching for bioastronomical signals from the farside of the Moon

| last=Maccone | first=Claudio

| title=Exo-/astro-biology. Proceedings of the First European Workshop

| editor1-first=P. | editor1-last=Ehrenfreund

| editor2-first=O. | editor2-last=Angerer

| editor3-first=B. | editor3-last=Battrick

| location=Noordwijk | publisher=ESA Publications Division

| isbn=978-92-9092-806-5 | volume=496

| pages=277–280 |date=August 2001

| bibcode=2001ESASP.496..277M | postscript=. }}

{{citation | first=Glenn | last=Chapmann | editor1-first=R. | editor1-last=Blackledge | editor2-first=C. | editor2-last=Radfield | editor3-first=S. | editor3-last=Seida | contribution=Space: the Ideal Place to Manufacture Microchips | title=Proceedings of the 10th International Space Development Conference | location=San Antonio, Texas | date=May 22–27, 1991 | pages=25–33 | url=http://deneb.ensc.sfu.ca/papers/sdc-91w.pdf | access-date=2010-01-12 | postscript=. | archive-url=https://web.archive.org/web/20110706202903/http://deneb.ensc.sfu.ca/papers/sdc-91w.pdf | archive-date=2011-07-06 }}

{{citation | title=History of the Use of Balloons in Scientific Experiments | last=Pfotzer | first=G. |date=June 1972 | journal=Space Science Reviews | volume=13 | issue=2 | pages=199–242 | doi=10.1007/BF00175313 | bibcode=1972SSRv...13..199P | s2cid=120710485 | postscript=. }}

{{citation | last1=Letessier-Selvon | first1=Antoine | last2=Stanev | first2=Todor | title=Ultrahigh energy cosmic rays | journal=Reviews of Modern Physics | volume=83 | issue=3 | pages=907–942 |date=July 2011 | doi=10.1103/RevModPhys.83.907 | bibcode=2011RvMP...83..907L | postscript=. |arxiv = 1103.0031 | s2cid=119237295 }}

{{citation|display-authors=1 |last1=Dimotakis |first1=P. |last2=Garwin |first2=R. |last3=Katz |first3=J. |last4=Vesecky |first4=J. |title=100 lbs to Low Earth Orbit (LEO): Small-Payload Launch Options |publisher=The Mitre Corporation |date=October 1999 |pages=1–39 |url=http://en.scientificcommons.org/18569633 |archive-url=https://web.archive.org/web/20170829090237/http://en.scientificcommons.org/18569633 |archive-date=2017-08-29 |access-date=2012-01-21 |postscript=. }}

{{citation | postscript=.

| contribution=The Local Interstellar Medium

| last=Redfield | first=S.

| title=New Horizons in Astronomy; Proceedings of the Conference Held 16–18 October 2005 at The University of Texas, Austin, Texas, USA

| series=Frank N. Bash Symposium ASP Conference Series

| volume=352 | page=79 | date=September 2006

| bibcode=2006ASPC..352...79R | arxiv=astro-ph/0601117 }}

{{citation | postscript=.

| title=The Temperature of the Cosmic Microwave Background

| last=Fixsen | first=D. J.

| journal=The Astrophysical Journal

| volume=707 | issue=2 | pages=916–920 | date=December 2009

| doi=10.1088/0004-637X/707/2/916 | arxiv=0911.1955

| bibcode=2009ApJ...707..916F | s2cid=119217397 }}

{{citation | postscript=.

| title=Getting to Low Earth Orbit | work=Space Future

| first=James V. H. | last=Hill | date=April 1999

| url=http://www.spacefuture.com/archive/getting_to_low_earth_orbit.shtml | url-status=live

| archive-url=https://web.archive.org/web/20120319163414/http://www.spacefuture.com/archive/getting_to_low_earth_orbit.shtml

| access-date=2012-03-18 | archive-date=2012-03-19 }}

{{citation | postscript=.

| title=Dynamics of the thermosphere

| last1=Forbes | first1=Jeffrey M.

| journal=Journal of the Meteorological Society of Japan

| series=Series II | pages=193–213 | volume=85B | year=2007

| doi=10.2151/jmsj.85b.193 |bibcode=2007JMeSJ..85B.193F |doi-access=free }}

{{citation | last1=Krumm | first1=N. | last2=Brosch | first2=N. | title=Neutral hydrogen in cosmic voids | journal=Astronomical Journal | volume=89 | pages=1461–1463 |date=October 1984 | doi=10.1086/113647 | bibcode=1984AJ.....89.1461K | postscript=. | doi-access=free }}

{{citation | display-authors=1 | last1=Bykov | first1=A. M. | last2=Paerels | first2=F. B. S. | last3=Petrosian | first3=V. | title=Equilibration Processes in the Warm-Hot Intergalactic Medium | journal=Space Science Reviews | volume=134 | issue=1–4 | pages=141–153 |date=February 2008 | doi=10.1007/s11214-008-9309-4 | bibcode=2008SSRv..134..141B | postscript=. |arxiv = 0801.1008 | s2cid=17801881 }}

{{citation | display-authors=1 | last1=Gupta | first1=Anjali | last2=Galeazzi | first2=M. | last3=Ursino | first3=E. | title=Detection and Characterization of the Warm-Hot Intergalactic Medium | journal=Bulletin of the American Astronomical Society | volume=41 | page=908 |date=May 2010 | bibcode=2010AAS...21631808G | postscript=. }}

{{citation | title=Geomagnetic Storms | date=January 14, 2011 | work=OECD/IFP Futures Project on "Future Global Shocks" | publisher=CENTRA Technology, Inc. | pages=1–69 | url=http://www.oecd.org/dataoecd/57/25/46891645.pdf | access-date=2012-04-07 | postscript=. | url-status=live | archive-url=https://web.archive.org/web/20120314111613/http://www.oecd.org/dataoecd/57/25/46891645.pdf | archive-date=March 14, 2012 }}

{{citation | title=Cepheid Variable Stars & Distance Determination | publisher=CSIRO Australia | date=October 25, 2004 | url=http://outreach.atnf.csiro.au/education/senior/astrophysics/variable_cepheids.html | access-date=2011-09-12 | postscript=. | url-status=live | archive-url=https://web.archive.org/web/20110830013526/http://outreach.atnf.csiro.au/education/senior/astrophysics/variable_cepheids.html | archive-date=August 30, 2011 }}

{{citation | postscript=.

| title=The Beginning of the World from the Point of View of Quantum Theory

| last=Lemaître | first=G. | author-link=Georges Lemaître

|date=May 1931 | journal=Nature

| volume=127 | issue=3210 | page=706

| doi=10.1038/127706b0 | doi-access=free

| bibcode=1931Natur.127..706L | s2cid=4089233 }}

{{citation | postscript=.

| title=Human Exposure to Vacuum

| last=Landis | first=Geoffrey A. | date=August 7, 2007

| publisher=www.geoffreylandis.com

| url=http://www.geoffreylandis.com/vacuum.html

| archive-url=https://web.archive.org/web/20090721182306/http://www.geoffreylandis.com/vacuum.html

| access-date=2009-06-19 | archive-date=July 21, 2009 }}

{{citation

| title=The Space Activity Suit: An Elastic Leotard for Extravehicular Activity

| last=Webb | first=P.

| journal=Aerospace Medicine

| year=1968 | volume=39 | issue=4 | pages= 376–383

| pmid=4872696 | postscript=. }}

{{citation |date=March 23, 2017 |title=Status of International Agreements relating to activities in outer space as of 1 January 2017 |publisher=United Nations Office for Outer Space Affairs/ Committee on the Peaceful Uses of Outer Space |url=http://www.unoosa.org/documents/pdf/spacelaw/treatystatus/AC105_C2_2017_CRP07E.pdf |access-date=2018-03-22 |postscript=. |archive-url=https://web.archive.org/web/20180322130911/http://www.unoosa.org/documents/pdf/spacelaw/treatystatus/AC105_C2_2017_CRP07E.pdf |archive-date=March 22, 2018 }}

{{citation |date=January 1, 2008 |title=Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies |publisher=United Nations Office for Outer Space Affairs |url=http://www.unoosa.org/oosa/SpaceLaw/outerspt.html |access-date=2009-12-30 |postscript=. |archive-url=https://web.archive.org/web/20110427091708/http://www.unoosa.org/oosa/SpaceLaw/outerspt.html |archive-date=April 27, 2011 }}

{{citation|title=Columbus launch puts space law to the test |date=November 5, 2007 |publisher=European Science Foundation |url=http://www.esf.org/research-areas/humanities/news/ext-news-singleview/article/columbus-launch-puts-space-law-to-the-test-358.html |access-date=2009-12-30 |postscript=. |archive-url=https://web.archive.org/web/20081215174524/http://www.esf.org/research-areas/humanities/news/ext-news-singleview/article/columbus-launch-puts-space-law-to-the-test-358.html |archive-date=December 15, 2008 }}

{{citation | first=Tony | last=Phillips | publisher=NASA | title=Cosmic Rays Hit Space Age High | date=September 29, 2009 | url=https://science.nasa.gov/headlines/y2009/29sep_cosmicrays.htm | access-date=2009-10-20 | postscript=. | archive-url=https://web.archive.org/web/20091014035616/http://science.nasa.gov/headlines/y2009/29sep_cosmicrays.htm | archive-date=2009-10-14 }}

{{citation | postscript=.

| title=Outer

| first=Douglas | last=Harper

| work=Online Etymology Dictionary

| url=http://www.etymonline.com/index.php?search=outer+space&searchmode=none | url-status=live

| archive-url=https://web.archive.org/web/20100312043648/http://www.etymonline.com/index.php?search=outer+space&searchmode=none

| access-date=2008-03-24 | archive-date=2010-03-12 }}

{{citation | first1=Paul | last1=Kintner | author2=GMDT Committee and Staff | url=http://ilwsonline.org/lwsgeospace_cospar.pdf | title=Report of the Living With a Star Geospace Mission Definition Team | date=September 2002 | publisher=NASA | access-date=2012-04-15 | postscript=. | url-status=live | archive-url=https://web.archive.org/web/20121102115356/http://ilwsonline.org/lwsgeospace_cospar.pdf | archive-date=2012-11-02 }}

{{citation|first1=David |last1=Portree |first2=Joseph |last2=Loftus |title=Orbital Debris: A Chronology |journal=NASA Sti/Recon Technical Report N |publisher=NASA | year=1999 |volume=99 |page=13 |bibcode=1999STIN...9941786P |url=http://ston.jsc.nasa.gov/collections/TRS/_techrep/TP-1999-208856.pdf |access-date=2012-05-05 |postscript=. |archive-url=https://web.archive.org/web/20000901071135/http://ston.jsc.nasa.gov/collections/TRS/_techrep/TP-1999-208856.pdf |archive-date=2000-09-01 }}

{{citation | postscript=.

| title=The temperature structure, mass, and energy flow in the corona and inner solar wind

| last=Withbroe | first=George L.

| journal=Astrophysical Journal, Part 1

| volume=325 |date=February 1988 | pages=442–467

| doi=10.1086/166015 | bibcode=1988ApJ...325..442W }}

{{citation | postscript=.

| title=NASA – IBEX Reveals a Missing Boundary at the Edge of the Solar System

| first=Karen C. | last=Fox

| date=May 10, 2012 | publisher=NASA

| url=http://www.nasa.gov/mission_pages/ibex/news/nobowshock.html | url-status=live

| archive-url=https://web.archive.org/web/20120512235338/http://www.nasa.gov/mission_pages/ibex/news/nobowshock.html

| access-date=2012-05-14 | archive-date=May 12, 2012 }}

{{citation | last1 = McComas | first1 = D. J. | last2 = Alexashov | first2 = D. | last3 = Bzowski | first3 = M. | last4 = Fahr | first4 = H. | last5 = Heerikhuisen | first5 = J. | last6 = Izmodenov | first6 = V. | last7 = Lee | first7 = M. A. | last8 = Mobius | first8 = E. | last9 = Pogorelov | first9 = N. | display-authors=1 | title = The Heliosphere's Interstellar Interaction: No Bow Shock | doi = 10.1126/science.1221054 | journal = Science | volume = 336 | issue = 6086 | pages = 1291–3 | date = 2012 | postscript=. |bibcode = 2012Sci...336.1291M | pmid=22582011| s2cid = 206540880 | doi-access = free }}

{{Citation | last1 = Forgan | first1 = Duncan H. | last2 = Elvis | first2 = Martin | title = Extrasolar asteroid mining as forensic evidence for extraterrestrial intelligence | journal = International Journal of Astrobiology | volume = 10 | issue = 4 | pages = 307–313 |date=October 2011 | doi = 10.1017/S1473550411000127 | bibcode = 2011IJAsB..10..307F | arxiv = 1103.5369 | s2cid = 119111392 | postscript= . }}

{{Citation | postscript=.

| title=Cosmic Background Explorer

| first=David T. | last=Chuss | date=June 26, 2008

| publisher=NASA Goddard Space Flight Center

| url=http://lambda.gsfc.nasa.gov/product/cobe/ | url-status=live

| archive-url = https://web.archive.org/web/20130509235348/http://lambda.gsfc.nasa.gov/product/cobe/

| access-date=2013-04-27 | archive-date=2013-05-09 }}

{{Citation | postscript= .

| title=Interstellar chemistry

| first=William | last=Klemperer

| journal=Proceedings of the National Academy of Sciences of the United States of America

| volume=103 | issue=33 | pages=12232–12234 | date=August 15, 2006

| doi=10.1073/pnas.0605352103 | doi-access=free | pmc=1567863

| bibcode=2006PNAS..10312232K | pmid=16894148 }}

{{Citation | last1 = Fang | first1 = T. | last2 = Buote | first2 = D. A. | last3 = Humphrey | first3 = P. J. | last4 = Canizares | first4 = C. R. | last5 = Zappacosta | first5 = L. | last6 = Maiolino | first6 = R. | last7 = Tagliaferri | first7 = G. | last8 = Gastaldello | first8 = F. | display-authors = 1 | doi = 10.1088/0004-637X/714/2/1715 | title = Confirmation of X-Ray Absorption by Warm-Hot Intergalactic Medium in the Sculptor Wall | journal = The Astrophysical Journal | volume = 714 | issue = 2 | page = 1715 | date = 2010 | postscript= . |arxiv = 1001.3692 |bibcode = 2010ApJ...714.1715F | s2cid = 17524108 }}

{{Citation | last1 = Wakker | first1 = B. P. | last2 = Savage | first2 = B. D. | doi = 10.1088/0067-0049/182/1/378 | title = The Relationship Between Intergalactic H I/O VI and Nearby (z<0.017) Galaxies | journal = The Astrophysical Journal Supplement Series | volume = 182 | issue = 1 | page = 378 | date = 2009 | postscript= . |arxiv = 0903.2259 |bibcode = 2009ApJS..182..378W | s2cid = 119247429 }}

{{Citation | last1 = Mathiesen | first1 = B. F. | last2 = Evrard | first2 = A. E. | doi = 10.1086/318249 | title = Four Measures of the Intracluster Medium Temperature and Their Relation to a Cluster's Dynamical State | journal = The Astrophysical Journal | volume = 546 | issue = 1 | page = 100 | date = 2001 | postscript= . |arxiv = astro-ph/0004309 |bibcode = 2001ApJ...546..100M | s2cid = 17196808 }}

{{Citation | last1 = Raggio | first1 = J. | last2 = Pintado | first2 = A. | last3 = Ascaso | first3 = C. | last4 = De La Torre | first4 = R. | last5 = De Los Ríos | first5 = A. | last6 = Wierzchos | first6 = J. | last7 = Horneck | first7 = G. | last8 = Sancho | first8 = L. G. | display-authors = 1 | title = Whole Lichen Thalli Survive Exposure to Space Conditions: Results of Lithopanspermia Experiment with Aspicilia fruticulosa | journal = Astrobiology | volume = 11 | issue = 4 | pages = 281–292 |date=May 2011 | doi = 10.1089/ast.2010.0588 | bibcode = 2011AsBio..11..281R | postscript= . | pmid=21545267}}

{{Citation | last1 = Tepfer | first1 = David | last2 = Zalar | first2 = Andreja | last3 = Leach | first3 = Sydney | display-authors = 1 | title = Survival of Plant Seeds, Their UV Screens, and nptII DNA for 18 Months Outside the International Space Station | journal = Astrobiology | volume = 12 | issue = 5 | pages = 517–528 | date = May 2012 | doi = 10.1089/ast.2011.0744 | bibcode = 2012AsBio..12..517T | url = http://eea.spaceflight.esa.int/attachments/spacestations/ID5017fe77cc303.pdf | access-date = 2013-05-19 | postscript = . | pmid = 22680697 | url-status=live | archive-url = https://web.archive.org/web/20141213201107/http://eea.spaceflight.esa.int/attachments/spacestations/ID5017fe77cc303.pdf | archive-date = 2014-12-13 }}

{{Citation | postscript=.

| title=Towards a General Theory of Lithopanspermia

| last1=Nicholson | first1=W. L.

| volume=1538

| work=Astrobiology Science Conference 2010

| pages=5272–528 |date=April 2010

| bibcode=2010LPICo1538.5272N }}

{{Citation | postscript=.

| title=Survival of Spores of the UV-ResistantBacillus subtilis Strain MW01 After Exposure to Low-Earth Orbit and Simulated Martian Conditions: Data from the Space Experiment ADAPT on EXPOSE-E

| last1=Wassmann | first1=Marko | last2=Moeller | first2=Ralf

| last3=Rabbow | first3=Elke | last4=Panitz | first4=Corinna

| last5=Horneck | first5=Gerda | last6=Reitz | first6=Günther

| last7=Douki | first7=Thierry | last8=Cadet | first8=Jean

| last9=Stan-Lotter | first9=Helga | last10=Cockell | first10=Charles S.

| last11=Rettberg | first11=Petra | display-authors=1

| journal=Astrobiology

| volume=12 | issue=5 | pages=498–507 | date=May 2012

| doi=10.1089/ast.2011.0772 | bibcode=2012AsBio..12..498W

| pmid=22680695}}

{{citation |last=Trimble |first=V. |year=1987 |title=Existence and nature of dark matter in the universe |journal=Annual Review of Astronomy and Astrophysics |volume=25 |pages=425–472 |bibcode=1987ARA&A..25..425T |doi=10.1146/annurev.aa.25.090187.002233|s2cid=123199266 |postscript = .|url=http://www.escholarship.org/uc/item/2hz008rs }}

{{citation | url=https://science.nasa.gov/astrophysics/focus-areas/what-is-dark-energy/ | title=Dark Energy, Dark Matter | work=NASA Science | access-date=May 31, 2013 | quote=It turns out that roughly 68% of the Universe is dark energy. Dark matter makes up about 27%. | postscript=. | url-status=live | archive-url=https://web.archive.org/web/20130602083852/http://science.nasa.gov/astrophysics/focus-areas/what-is-dark-energy/ | archive-date=June 2, 2013 }}

{{citation

| last1=Peebles | first1=P. | last2=Ratra | first2=B.

| doi=10.1103/RevModPhys.75.559

| title=The cosmological constant and dark energy

| journal=Reviews of Modern Physics

| volume=75 | issue=2 | pages=559–606 | year=2003

| arxiv=astro-ph/0207347 | bibcode=2003RvMP...75..559P

| s2cid=118961123 }}

{{citation

| display-authors=1

| last1 = Assis

| first1 = A. K. T.

| last2 = Paulo

| first2 = São

| last3 = Neves

| first3 = M. C. D.

| title = History of the 2.7 K Temperature Prior to Penzias and Wilson

| journal = Apeiron

| volume = 2

| issue = 3

| pages = 79–87

| date =July 1995

| postscript = .

}}

{{citation | postscript=.

| title=Origin of the Universe

| last=Turner | first=Michael S.

| journal=Scientific American

| volume=301 | issue=3 | pages=36–43 | date=September 2009

| doi=10.1038/scientificamerican0909-36 | pmid=19708526

| bibcode=2009SciAm.301c..36T }}

{{citation | postscript=.

| title=WMAP – Shape of the universe

| publisher=NASA | date=December 21, 2012

| url=http://map.gsfc.nasa.gov/universe/uni_shape.html | url-status=live

| archive-url=https://web.archive.org/web/20120601032707/http://map.gsfc.nasa.gov/universe/uni_shape.html

| access-date=June 4, 2013 | archive-date=June 1, 2012 }}

{{citation

| last1=Leinert | first1=C.

| last2=Grun | first2=E.

| title=Physics of the Inner Heliosphere I

| chapter=Interplanetary Dust

| page=207

| year=1990

| doi=10.1007/978-3-642-75361-9_5

| bibcode=1990pihl.book..207L

| isbn=978-3-642-75363-3

| postscript=.

}}

{{citation | postscript=.

| title=Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences – Origin and early evolution of solid matter in the Solar System

| last=Witt | first=Adolf N.

| contribution=The Chemical Composition of the Interstellar Medium

| volume=359 | issue=1787 | page=1949 | date=October 2001

| bibcode=2001RSPTA.359.1949W

| s2cid=91378510 | doi=10.1098/rsta.2001.0889 }}

{{citation | postscript=.

| last=Tyson |first=Patrick | date=January 2012

| title=The Kinetic Atmosphere: Molecular Numbers

| url=http://www.climates.com/KA/BASIC%20PARAMETERS/molecularnumbers.pdf

| archive-url=https://web.archive.org/web/20131207001720/http://www.climates.com/KA/BASIC%20PARAMETERS/molecularnumbers.pdf

| archive-date=7 December 2013 | access-date=13 September 2013 }}

{{citation

| display-authors=1

| last1=Burton | first1=Rodney

| last2=Brown | first2=Kevin

| last3=Jacobi | first3=Anthony

| title=Low-Cost Launch of Payloads to Low Earth Orbit

| journal=Journal of Spacecraft and Rockets

| date=May 2005

| volume=43

| issue=3

| pages=696–698

| bibcode=2006JSpRo..43..696B

| doi=10.2514/1.16244

| postscript=.

}}

{{citation | postscript=.

| title=The interstellar environment of our galaxy

| first=Katia M. | last=Ferrière

| journal=Reviews of Modern Physics

| volume=73 | issue=4 | pages=1031–1066 | year=2001

| doi=10.1103/RevModPhys.73.1031 | s2cid=16232084

| bibcode=2001RvMP...73.1031F | arxiv=astro-ph/0106359 }}

{{citation|url=http://www.livescience.com/34085-space-smell.html|title=What Does Space Smell Like?|publisher=Live Science|date=July 20, 2012|access-date=February 19, 2014|postscript=.|url-status=live|archive-url=https://web.archive.org/web/20140228045646/http://www.livescience.com/34085-space-smell.html|archive-date=February 28, 2014}}

{{citation | postscript=.

| title=What Does Space Smell Like

| first=Lizzie | last=Schiffman

| publisher=Popular Science | date=July 17, 2013

| url=http://www.popsci.com/science/article/2013-07/what-does-space-smell | url-status=live

| archive-url=https://web.archive.org/web/20140224030433/http://www.popsci.com/science/article/2013-07/what-does-space-smell

| access-date=February 19, 2014 | archive-date=February 24, 2014}}

{{citation|last=Wall|first=Mike|title=Voyager 1 Has Left Solar System|url=http://m.space.com/22729-voyager-1-spacecraft-interstellar-space.html|date=September 12, 2013|work=Web|publisher=Space.com|access-date=13 September 2013|postscript=.|url-status=live|archive-url=https://web.archive.org/web/20130914044506/http://m.space.com/22729-voyager-1-spacecraft-interstellar-space.html|archive-date=14 September 2013}}

{{citation | author=Planck Collaboration | title= Planck 2013 results. I. Overview of products and scientific results | journal=Astronomy & Astrophysics | year=2014 | volume=571 | page=1 | doi=10.1051/0004-6361/201321529 | bibcode=2014A&A...571A...1P | arxiv= 1303.5062 | s2cid= 218716838 | postscript=.}}

{{citation

| title=NASA's Hubble Provides First Census of Galaxies Near Cosmic Dawn

| display-authors=1 | last1=Harrington | first1=J. D.

| last2=Villard | first2=Ray | last3=Weaver | first3=Donna

| id=12-428 | date=December 12, 2012 | publisher=NASA

| url = http://hubblesite.org/newscenter/archive/releases/survey/hubble-ultra-deep-field/2012/48/

| postscript=. | url-status=live

| archive-url = https://web.archive.org/web/20150322081210/http://hubblesite.org/newscenter/archive/releases/survey/hubble-ultra-deep-field/2012/48/

| archive-date=22 March 2015 }}

{{citation | postscript=.

| title=Looking for Cosmic Neutrino Background

| last=Chiaki | first=Yanagisawa

| journal=Frontiers in Physics

| date=June 2014 | volume=2 | page=30

| bibcode=2014FrP.....2...30Y

| doi=10.3389/fphy.2014.00030 | doi-access=free }}

{{citation | postscript=.

| title=How do we know when Voyager reaches interstellar space?

| work=JPL News | date=September 12, 2013

| first=Jia-Rui | last=Cook | id=2013-278

| url=http://www.jpl.nasa.gov/news/news.php?release=2013-278 | url-status=live

| archive-url=https://web.archive.org/web/20130915060510/http://www.jpl.nasa.gov/news/news.php?release=2013-278

| archive-date=September 15, 2013 }}

{{citation | postscript=.

| title=Interplanetary space | work=Universe Today

| first=Abby | last=Cessna | date=July 5, 2009

| url=http://www.universetoday.com/34074/interplanetary-space/ | url-status=live

| archive-url=https://web.archive.org/web/20150319173041/http://www.universetoday.com/34074/interplanetary-space/

| archive-date=March 19, 2015 }}

.{{citation

| title = Where does space begin?

| url = http://aerospaceengineering.aero/where-does-space-begin/

| website = Aerospace Engineering |access-date = 2015-11-10

| language = en-US |url-status=live | postscript=.

| archive-url = https://web.archive.org/web/20151117034012/http://aerospaceengineering.aero/where-does-space-begin/

| archive-date = 2015-11-17}}

{{citation

| title=The cislunar gateway with no gate

| first=John K. | last=Strickland | date=October 1, 2012

| url=http://www.thespacereview.com/article/2165/1

| publisher=The Space Review | access-date=2016-02-10

| url-status=live | postscript=.

| archive-url=https://web.archive.org/web/20160207003135/http://www.thespacereview.com/article/2165/1

| archive-date=February 7, 2016 }}

{{citation

| title=Galactic hydrostatic equilibrium with magnetic tension and cosmic-ray diffusion

| last1=Boulares | first1=Ahmed | last2=Cox | first2=Donald P.

| journal=Astrophysical Journal, Part 1

| volume=365 | pages=544–558 | date=December 1990

| doi=10.1086/169509 | bibcode=1990ApJ...365..544B | postscript=. }}

{{citation

| title = Galaxies and their Masks: A Conference in Honour of K.C. Freeman, FRS

| last1=Wielebinski | first1=Richard | last2=Beck

| first2=Rainer | editor1-last=Block | editor1-first=David L.

| editor2-last=Freeman | editor2-first=Kenneth C.

| editor3-last=Puerari | editor3-first=Ivânio

| contribution=Cosmic Magnetic Fields − An Overview

| publisher=Springer Science & Business Media

| pages=67–82 | year=2010 | isbn=978-1-4419-7317-7 | postscript=.

| doi=10.1007/978-1-4419-7317-7_5 | bibcode=2010gama.conf...67W

| url = https://books.google.com/books?id=PK7MoOWD-F8C&pg=PA67

| url-status=live

| archive-url = https://web.archive.org/web/20170920155433/https://books.google.com/books?id=PK7MoOWD-F8C&pg=PA67

| archive-date=2017-09-20 }}

{{citation

| title=The Earth's Magnetotail

| first=Edward W. Jr. | last=Hones

| journal=Scientific American

| volume=254 | issue=3 | date=March 1986 | pages=40–47

| doi=10.1038/scientificamerican0386-40 | jstor=24975910| bibcode=1986SciAm.254c..40H}}

{{citation

| contribution=Definition of 'deep space'

| title=Collins English Dictionary

| url = https://www.collinsdictionary.com/us/dictionary/english/deep-space

| access-date=2018-01-15 | postscript=. }}

{{citation

| title=Novae in Spiral Nebulae and the Island Universe Theory

| last=Curtis | first=Heber D.

| journal=Publications of the Astronomical Society of the Pacific

| volume=100 | pages=6–7 | date=January 1988

| doi=10.1086/132128 | bibcode=1988PASP..100....6C | postscript=. | doi-access=free }}

{{citation

| title=Interstellar Travel: A Review for Astronomers

| last=Crawford | first=I. A.

| journal=Quarterly Journal of the Royal Astronomical Society

| volume=31 | pages=377–400 | date=September 1990

| bibcode=1990QJRAS..31..377C | postscript=. }}

{{citation

| title=A Shifting Shield Provides Protection Against Cosmic Rays

| first=Susanna | last=Kohler | date=December 1, 2017

| work=Nova | page=2992 | publisher=American Astronomical Society

| bibcode=2017nova.pres.2992K | url = https://aasnova.org/2017/12/01/a-shifting-shield-provides-protection-against-cosmic-rays/

| access-date=2019-01-31 | postscript=. }}

{{citation

| title=ALMA reveals ghostly shape of 'coldest place in the universe'

| date=October 24, 2013 | publisher=National Radio Astronomy Observatory

| url = https://phys.org/news/2013-10-alma-reveals-ghostly-coldest-universe.html

| access-date=2020-10-07 | postscript=. }}

{{citation | postscript=.

| title=India Enters the Elite Club: Successfully Shot Down Low Orbit Satellite

| last=Solanki | first=Lalit

| journal=The Mirk | date=March 27, 2019

| url=https://themirk.com/india-enters-the-elite-club-successfully-shot-down-low-orbit-satellite/

| access-date=2019-03-28 | archive-date=2019-03-28

| archive-url=https://web.archive.org/web/20190328134405/https://themirk.com/india-enters-the-elite-club-successfully-shot-down-low-orbit-satellite/

| url-status=dead }}

{{citation

| url=http://life.itu.int/radioclub/rr/art1.pdf

| title=ITU-R Radio Regulations, Article 1, Terms and definitions, Section VIII, Technical terms relating to space, paragraph 1.177.

| publisher=International Telecommunication Union

| access-date=2018-02-05 | postscript=.

| quote=1.177 deep space: Space at distances from the Earth equal to, or greater than, {{val|2|e=6|u=km}} }}

{{citation

| url=https://www.thenation.com/article/archive/apollo-space-lunar-rockets-colonialism/

| title=Is Spaceflight Colonialism? | postscript=.

| first=Haris | last=Durrani | work=The Nation

| access-date=6 October 2020 | date=19 July 2019 }}

{{citation

| first=Maura | last=Brady

| title=Space and the Persistence of Place in "Paradise Lost"

| journal=Milton Quarterly | postscript=.

| volume=41 | issue=3 | date=October 2007 | pages=167–182

| doi=10.1111/j.1094-348X.2007.00164.x | jstor=24461820 }}

{{citation

| title=Definition of SPACEBORNE

| website=Merriam-Webster

| date=May 17, 2022 | postscript=.

| url=https://www.merriam-webster.com/dictionary/spaceborne

| access-date=2022-05-18}}

{{citation

| title=Spaceborne definition and meaning

| website=Collins English Dictionary

| date=May 17, 2022 | postscript=.

| url=https://www.collinsdictionary.com/dictionary/english/spaceborne

| access-date=2022-05-18}}

{{citation | postscript=.

| url=https://history.nasa.gov/ap08fj/03day1_green_sep.htm

| title=Day 1: The Green Team and Separation

| last1=Woods | first1=W. David | last2=O'Brien | first2=Frank

| year=2006 | work=Apollo 8 Flight Journal |publisher=NASA

| access-date=October 29, 2008

| archive-url=https://web.archive.org/web/20080923012425/http://history.nasa.gov/ap08fj/03day1_green_sep.htm

| archive-date=September 23, 2008 }} TIMETAG 003:42:55.

{{citation | postscript=.

| title=What Is a Geosynchronous Orbit?

| last=Howell | first=Elizabeth

| work=Space.com | date=April 24, 2015

| url=https://www.space.com/29222-geosynchronous-orbit.html

| access-date=8 December 2022 }}

{{citation | postscript=.

| title=Enhanced radiative cooling paint with broken glass bubbles

| last1=Yu | first1=Xinxian | last2=Yao | first2=Fengju

| last3=Huang | first3=Wenjie | last4=Xu | first4=Dongyan

| last5=Chen | first5=Chun | display-authors=1

| url=https://www.sciencedirect.com/science/article/pii/S0960148122007418

| journal=Renewable Energy

| volume=194 | pages=129–136 | date=July 2022

| via=Elsevier Science Direct

| doi=10.1016/j.renene.2022.05.094 | bibcode=2022REne..194..129Y

|s2cid=248972097

| quote=Radiative cooling does not consume external energy but rather harvests coldness from outer space as a new renewable energy source. }}

{{citation | postscript=.

| title=Flexible Daytime Radiative Cooling Enhanced by Enabling Three-Phase Composites with Scattering Interfaces between Silica Microspheres and Hierarchical Porous Coatings

| last=Ma |first=Hongchen

| url=https://pubs.acs.org/doi/abs/10.1021/acsami.1c02145

| journal=ACS Applied Materials & Interfaces

| via=ACS Publications

| volume=13 | issue=16 | pages=19282–19290 | year=2021

| doi=10.1021/acsami.1c02145 | pmid=33866783

| arxiv=2103.03902 | s2cid=232147880

| quote=Daytime radiative cooling has attracted considerable attention recently due to its tremendous potential for passively exploiting the coldness of the universe as clean and renewable energy. }}

{{citation | postscript=.

| title=Radiative cooling through the atmospheric window: A third, less intrusive geoengineering approach

| last1=Zevenhovena | first1=Ron | last2=Fält | first2=Martin

| url=https://www.sciencedirect.com/science/article/abs/pii/S0360544218304936

| journal=Energy | volume=152 | date=June 2018

| page=27

| doi=10.1016/j.energy.2018.03.084

| bibcode=2018Ene...152...27Z

| via=Elsevier Science Direct

| quote=An alternative, third geoengineering approach would be enhanced cooling by thermal radiation from the Earth's surface into space. }}

{{citation | postscript=.

| title=A structural polymer for highly efficient all-day passive radiative cooling

| last1=Wang | first1=Tong | last2=Wu | first2=Yi

| last3=Shi | first3=Lan | last4=Hu | first4=Xinhua

| last5=Chen | first5=Min | last6=Wu | first6=Limin

| journal=Nature Communications | display-authors=1

| volume=12 | issue=365 | page=365 | year=2021

| doi=10.1038/s41467-020-20646-7 | pmid=33446648 | pmc=7809060

| quote=One possibly alternative approach is passive radiative cooling—a sky-facing surface on the Earth spontaneously cools by radiating heat to the ultracold outer space through the atmosphere's longwave infrared (LWIR) transparency window (λ ~ 8–13 μm). }}

{{citation | postscript=.

| title=Heat-shedding with photonic structures: radiative cooling and its potential

| last1=Heo | first1=Se-Yeon | display-authors=1

| last2=Ju Lee | first2=Gil | last3=Song | first3=Young Min

| url=https://pubs.rsc.org/en/content/articlelanding/2022/tc/d2tc00318j

| journal=Journal of Materials Chemistry C

| volume=10 | issue=27 | pages=9915–9937

| date=June 2022 | via=Royal Society of Chemistry

| doi=10.1039/D2TC00318J | s2cid=249695930 }}

{{citation | postscript=.

| title=Vacuum Technology

| first=A. | last=Roth

| page=6 | year=2012

| isbn=978-0-444-59874-5 | publisher=Elsevier

| url=https://books.google.com/books?id=oBqs3sr9r48C&pg=PA6 }}

{{citation | postscript=.

| title=False Dawn

| url=http://www.eso.org/public/images/potw1707a/

| website=www.eso.org

| access-date=14 February 2017 }}

{{citation | postscript=.

| author=NASA

| title=What scientists found after sifting through dust in the solar system

| url=https://www.eurekalert.org/pub_releases/2019-03/nsfc-wsf031219.php

| date=March 12, 2019 | work=EurekAlert!

| access-date=12 March 2019 }}

{{citation | postscript=.

| title=42 USC 18302: Definitions

| website=uscode.house.gov | date=December 15, 2022

| url=https://uscode.house.gov/view.xhtml?req=(title:42%20section:18302%20edition:prelim)#:~:text=(7)%20Near%2DEarth%20space,and%20includes%20geo%2Dsynchronous%20orbit.

| language=rw | access-date=December 17, 2022}}

{{citation | postscript=.

| title=Why We Explore | website=NASA | date=June 13, 2013

| url=http://www.nasa.gov/exploration/whyweexplore/why_we_explore_main.html

| access-date=December 17, 2022}}

{{citation | postscript=.

| title=Barotrauma

| display-authors=1 | first1=Amanda S. | last1=Battisti

| first2=Anthony | last2=Haftel | first3=Heather M. | last3=Murphy-Lavoie

| date=June 27, 2022

| publisher=StatPearls Publishing LLC

| pmid=29493973

| url=https://www.ncbi.nlm.nih.gov/books/NBK482348/

| access-date=2022-12-18 }}

{{citation | postscript=.

| title=FAA Commercial Space Astronaut Wings Program

| publisher=Federal Aviation Administration | date=July 20, 2021

| url=https://www.faa.gov/documentLibrary/media/Order/FAA_Order_8800.2.pdf

| access-date=2022-12-18 }}

{{citation | postscript=.

| last=Busby | first=D. E. | date=July 1967

| title=A prospective look at medical problems from hazards of space operations

| id=NASA-CR-856 | publisher=NASA

| series=Clinical Space Medicine

| url=https://ntrs.nasa.gov/api/citations/19670023576/downloads/19670023576.pdf

| access-date=2022-12-20 }}

{{citation | postscript=.

| title=The Temperature of Interstellar Matter. I

| last=Spitzer | first=Lyman Jr. | author-link=Lyman Spitzer

| journal=Astrophysical Journal

| volume=107 | page=6 | date=January 1948

| doi=10.1086/144984 | bibcode=1948ApJ...107....6S }}

{{citation | postscript=.

| title= 51 U.S.C 10101 -National and Commercial Space Programs, Subtitle I-General, Chapter 101-Definitions

| website=United States Code

| url=https://uscode.house.gov/view.xhtml?req=granuleid:USC-prelim-title51-section10101&num=0&edition=prelim

| publisher=Office of Law Revision Council, U. S. House of Representatives

| access-date=January 5, 2023 }}

{{citation | postscript=.

| title=The edge of space: Revisiting the Karman Line

| last=McDowell | first=Jonathan C.

| journal=Acta Astronautica

| volume=151 | pages=668–677 | date=October 2018

| doi=10.1016/j.actaastro.2018.07.003 | arxiv=1807.07894

| bibcode=2018AcAau.151..668M }}

{{citation | postscript=.

| title=Big Bang Cosmology | publisher=NASA

| url=https://map.gsfc.nasa.gov/universe/bb_theory.html

| access-date=2024-04-24 }}

{{citation | postscript=.

| title=Cosmological simulations of intergalactic medium enrichment from galactic outflows

| last1=Oppenheimer | first1=Benjamin D. | last2=Davé | first2=Romeel

| journal=Monthly Notices of the Royal Astronomical Society

| volume=373 | issue=4 | pages=1265–1292 | date=December 2006

| doi=10.1111/j.1365-2966.2006.10989.x | doi-access=free

| arxiv=astro-ph/0605651

| bibcode=2006MNRAS.373.1265O }}

{{citation | postscript=.

| title=Aerospace Pressure Effects

| display-authors=1 | first1=William J. | last1=Tarver

| first2=Keith | last2=Volner | first3=Jeffrey S. | last3=Cooper

| publisher=StatPearls Publishing | date=October 24, 2022

| publication-place=Treasure Island, FL

| url=https://europepmc.org/article/NBK/nbk470190

| pmid=29262037 | access-date=2024-04-25 }}

{{citation | postscript=.

| title=The population of natural Earth satellites

| display-authors=1 | last1=Granvik | first1=Mikael

| last2=Vaubaillon | first2=Jeremie | last3=Jedicke | first3=Robert

| journal=Icarus

| volume=218 | issue=1 | pages=262–277 | date=March 2012

| doi=10.1016/j.icarus.2011.12.003 | arxiv=1112.3781

| bibcode=2012Icar..218..262G }}

{{citation | postscript=.

| title=ESIL Reflection – Clearing up the Space Junk – On the Flaws and Potential of International Space Law to Tackle the Space Debris Problem – European Society of International Law

| website=European Society of International Law

| date=March 9, 2023

| url=https://esil-sedi.eu/esil-reflection-clearing-up-the-space-junk-on-the-flaws-and-potential-of-international-space-law-to-tackle-the-space-debris-problem/

| access-date=2024-04-24}}

{{citation | postscript=.

| title=Space Foundation Releases The Space Report 2023 Q2, Showing Annual Growth of Global Space Economy to $546B

| website=Space Foundation | date=July 25, 2023

| url=https://www.spacefoundation.org/2023/07/25/the-space-report-2023-q2/

| access-date=2024-04-24}}

{{citation | postscript=.

| title=In a world of drones and satellites, why use a spy balloon anyway?

| last=Bisset | first=Victoria

| newspaper=Washington Post | date=February 4, 2023

| url=https://www.washingtonpost.com/national-security/2023/02/04/china-spy-balloon-montana-why/

| access-date=2024-04-24}}

{{citation | postscript=.

| title=Intergalactic medium

| website=Harvard & Smithsonian

| date=June 16, 2022

| url=https://www.cfa.harvard.edu/research/topic/intergalactic-medium

| access-date=2024-04-16}}

{{citation | postscript=.

| title=Photo Gallery

| publisher=ARES | NASA Orbital Debris Program Office

| url=https://orbitaldebris.jsc.nasa.gov/photo-gallery/

| access-date=2024-04-27 }}

The semi-major axis of the Moon's orbit is {{val|384400|u=km|fmt=commas}}, which is 19.2% of two million km, or about one-fifth.

{{citation | postscript=.

| title=Moon Fact Sheet

| first=David R. | last=Williams

| date=December 20, 2021 | publisher=NASA

| url=https://nssdc.gsfc.nasa.gov/planetary/factsheet/moonfact.html | access-date=2023-09-23 }}

{{citation | postscript=.

| title=-based | year=2024

| work=Cambridge Dictionary

| url=https://dictionary.cambridge.org/us/dictionary/english/based

| access-date=2024-04-28 }}

{{citation | postscript=.

| title=Frequently Asked Questions

| publisher=Astromaterials Research & Exploration Science: NASA Orbital Debris Program Office

| url=https://orbitaldebris.jsc.nasa.gov/faq/#

| access-date=2024-04-29 }}

{{citation | postscript=.

| title=The solar discs that could power Earth

| first1=Amanda Jane | last1=Hughes | first2=Stefania | last2=Soldini

| date=November 26, 2020 | publisher=BBC

| url=https://www.bbc.com/future/article/20201126-the-solar-discs-that-could-beam-power-from-space

| access-date=2024-05-29 }}

{{citation | postscript=.

| title=Applicable definitions of outer space, space, and expanse

| work=Merriam-Webster dictionary

| url=https://www.merriam-webster.com/dictionary/

| access-date=2024-06-17

| quote=
Outer space (n.) space immediately outside the earth's atmosphere.
Space (n.) physical space independent of what occupies it. The region beyond the earth's atmosphere or beyond the solar system.
Expanse (n.) great extent of something spread out. }}

{{citation | postscript=.

| title=Torricelli and the Ocean of Air: The First Measurement of Barometric Pressure

| first=John B. | last=West

| journal=Physiology (Bethesda)

| date=March 2013 | volume=28 | issue=2 | pages=66–73

| pmc=3768090 | pmid=23455767 | doi=10.1152/physiol.00053.2012 }}

{{citation | postscript=.

| title=Cosmic Times

| website=Imagine the Universe!

| date=December 8, 2017

| url=https://imagine.gsfc.nasa.gov/educators/programs/cosmictimes/educators/guide/age_size.html

| access-date=October 31, 2024 }}

{{citation | postscript=.

| title=Space Weather Effects in the Earth's Radiation Belts

| last1=Baker | first1=D. N. | last2=Erickson | first2=P. J.

| last3=Fennell | first3=J. F. | last4=Foster | first4=J. C.

| last5=Jaynes | first5=A. N. | last6=Verronen | first6=P. T.

| display-authors=1 | journal=Space Science Reviews

| volume=214 | issue=1 | at=id. 17 | date=February 2018

| doi=10.1007/s11214-017-0452-7 | bibcode=2018SSRv..214...17B | doi-access=free }}

{{citation | postscript=.

| contribution=Utilization potential for distinct orbit families in the cislunar domain

| last1=Cunio | first1=P. M. | last2=Bever | first2=M.

| last3=Ingram | first3=C. | last4=Flewelling | first4=B. R.

| last5=McNeill | first5=G. | display-authors=1

| title=Advanced Maui Optical and Space Surveillance Technologies Conference (AMOS), Maui, HI, USA: Maui Economic Development Board

| year=2021

| url=https://amostech.com/TechnicalPapers/2021/Poster/Cunio.pdf

| access-date=2025-03-09 }}

{{citation | postscript=.

| title=Interesting Fact of the Month 2021

| website=NASA | date=August 3, 2023

| url=https://www.nasa.gov/space-science-and-astrobiology-at-ames/interesting-fact-of-the-month-current/interesting-fact-of-the-month-2021/

| access-date=2024-09-18}}

{{citation | postscript=.

| title=What does space smell like?

| last=Cooper | first=Keith

| website=Space.com | date=January 8, 2024

| url=https://www.space.com/what-does-space-smell-like

| access-date=2024-09-18 }}

{{citation | postscript=.

| title=The Kármán Line: Where space begins

| last=Betz | first=Eric

| website=Astronomy Magazine | date=November 27, 2023

| url=https://www.astronomy.com/space-exploration/the-karman-line-where-does-space-begin/

| access-date=2024-04-30 }}

{{citation | postscript=.

| title=Why defining the boundary of space may be crucial for the future of spaceflight

| last=Grush | first=Loren

| website=The Verge | date=December 13, 2018

| url=https://www.theverge.com/2018/12/13/18130973/space-karman-line-definition-boundary-atmosphere-astronauts

| access-date=2024-04-30 }}

{{citation | postscript=.

| contribution=Very Low Earth Orbit mission concepts for Earth Observation: Benefits and challenges

| first1=Josep Virgili | last1=Llop | first2=Peter C. E. | last2=Roberts

| first3=Zhou | last3=Hao | first4=Laia Ramio | last4=Tomas

| first5=Valentin | last5=Beauplet | display-authors=1

| title=Reinventing Space Conference | year=2014

| url=https://research.manchester.ac.uk/en/publications/very-low-earth-orbit-mission-concepts-for-earth-observation-benef

| access-date=2025-03-09 }}

{{citation | postscript=.

| last1=LaForge | first1=L. E. | last2=Moreland | first2=J. R.

| last3=Bryan | first3=R. G. | last4=Fadali | first4=M. S.

| title=Vertical Cavity Surface Emitting Lasers for Spaceflight Multi-Processors

| display-authors=1 | publisher=IEEE | year=2006 | pages=1–19

| isbn=978-0-7803-9545-9 | doi=10.1109/AERO.2006.1655895 }}

{{citation | postscript=.

| title=Satellite Drag

| website=NOAA / NWS Space Weather Prediction Center

| date=March 9, 2025

| url=https://www.swpc.noaa.gov/impacts/satellite-drag

| access-date=2025-03-10}}

{{citation | postscript=.

| title=Catalog of Earth Satellite Orbits

| work=NASA Earth Observatory

| first=Holli | last=Riebeek | date=September 4, 2009

| url=https://earthobservatory.nasa.gov/features/OrbitsCatalog

| access-date=2025-03-09 }}

{{citation | postscript=.

| title=Space Weather Effects in the Earth's Radiation Belts

| last1=Baker | first1=D. N. | last2=Erickson | first2=P. J.

| last3=Fennell | first3=J. F. | last4=Foster | first4=J. C.

| last5=Jaynes | first5=A. N. | last6=Verronen | first6=P. T.

| display-authors=1 | journal=Space Science Reviews

| volume=214 | issue=1 | year=2018

| issn=0038-6308 | doi=10.1007/s11214-017-0452-7 | doi-access=free

| bibcode=2018SSRv..214...17B

| url=https://link.springer.com/content/pdf/10.1007%2Fs11214-017-0452-7.pdf

| access-date=2025-03-10 }}

{{citation | postscript=.

| title=Earth's Magnetosphere, Electrons & Protons

| website=Encyclopedia Britannica | date=February 24, 2025

| url=https://www.britannica.com/science/Van-Allen-radiation-belt

| access-date=2025-03-10}}

{{citation | postscript=.

| contribution=Little LEO Satellites

| title=Doppler Applications in LEO Satellite Communication Systems

| first1=Irfan | last1=Ali | first2=Pierino G. | last2=Bonanni

| first3=Naofal | last3=Al-Dhahir | first4=John E. | last4=Hershey

| display-authors=1 | volume=656 | year=2002

| series=The Springer International Series in Engineering and Computer Science

| pages=1–26

| doi=10.1007/0-306-47546-4_1

| isbn=0-7923-7616-1

| url=https://link.springer.com/chapter/10.1007/0-306-47546-4_1

| access-date=2025-03-09 }}

{{citation | postscript=.

| title=Nuclear Detonations in Space: Reducing Risks to Low Earth Orbit Satellites

| first=Tyler | last=Koteskey | date=November 5, 2024

| work=Georgetown Security Studies Review

| url=https://georgetownsecuritystudiesreview.org/2024/11/05/nuclear-detonations-in-space-reducing-risks-to-low-earth-orbit-satellites/

| access-date=2025-03-09 | quote=The inner Van Allen belt overlaps with the upper edge of low-earth orbit }}

{{citation | postscript=.

| title=Measurement of cosmic radiation in LEO by 1U CubeSat☆

| first1=Pavel | last1=Kovar | first2=Marek | last2=Sommer

| first3=Daniel | last3=Matthiae | first4=Guenther | last4=Reitz

| display-authors=1 | journal=Radiation Measurements

| volume=139 | date=December 2020

| doi=10.1016/j.radmeas.2020.106471

| bibcode=2020RadM..13906471K

| quote=The radiation field in low Earth orbit (LEO) comprises a third radiation source, the Van Allen radiation belts... }}

{{citation | postscript=.

| title=Interplanetary trajectories | website=ESA

| url=https://www.esa.int/Science_Exploration/Space_Science/Interplanetary_trajectories

| access-date=2025-03-08}}

{{citation | postscript=.

| title=Interstellar space: What is it and where does it begin?

| first=Keith | last=Cooper

| website=Space.com | date=January 17, 2023

| url=https://www.space.com/interstellar-space-definition-explanation

| access-date=2024-01-30 | language=en}}

{{citation | postscript=.

| title=Atmospheric Evolution on Inhabited and Lifeless Worlds

| first1=David C. | last1=Catling | first2=James F. | last2=Kasting

| year=2017 | page=4 | isbn=9781316824528

| publisher=Cambridge University Press

| bibcode=2017aeil.book.....C

| url=https://books.google.com/books?id=2nuJDgAAQBAJ&pg=PA4 }}

{{citation | postscript=.

| title=Regulatory Dilemmas of Suborbital Flight

| last=Malinowski | first=Bartosz

| chapter=The Legal Status of Suborbital Aviation Within the International Regulatory Framework for Air and Space Use

| series=Space Regulations Library

| publisher=Springer Nature Switzerland | publication-place=Cham

| volume=10 | year=2024 | pages=13–43 | isbn=978-3-031-75086-1

| doi=10.1007/978-3-031-75087-8_2}}

{{citation | postscript=.

| title=Exploring Near Space: Myths, Realities, and Military Implications

| website=CAPS India | date=April 6, 2024

| url=https://capsindia.org/exploring-near-space-myths-realities-and-military-implications/

| access-date=2025-03-11}}

{{citation | postscript=.

| title=Why Don't Satellites Fall Out of the Sky?

| date=March 11, 2025

| url=https://www.nesdis.noaa.gov/news/why-dont-satellites-fall-out-of-the-sky

| website=National Environmental Satellite, Data, and Information Service

| access-date=2025-03-12 | language=en}}

{{citation | postscript=.

| first=David R. | last=Williams | date=November 17, 2010

| title=Earth Fact Sheet | work=Lunar & Planetary Science | publisher=NASA

| url=http://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html | url-status=live

| archive-url=https://web.archive.org/web/20101030234253/http://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html

| access-date=2012-05-10 | archive-date=October 30, 2010 }}

{{citation | postscript=.

| title=Star-Exoplanet Interactions: A Growing Interdisciplinary Field in Heliophysics

| last1=Garcia-Sage | first1=K. | last2=Farrish | first2=A. O.

| last3=Airapetian | first3=V. S. | last4=Alexander | first4=D.

| last5=Cohen | first5=O. | last6=Domagal-Goldman | first6=S.

| last7=Dong | first7=C. | last8=Gronoff | first8=G.

| last9=Halford | first9=A. J. | last10=Lazio | first10=J.

| last11=Luhmann | first11=J. G. | last12=Schwieterman | first12=E.

| last13=Sciola | first13=A. | last14=Segura | first14=A.

| last15=Toffoletto | first15=F. | last16=Vievering | first16=J.

| last17=Ahmed | first17=Md Redyan | last18=Bali | first18=K.

| last19=Rau | first19=G. | display-authors=1

| journal=Frontiers in Astronomy and Space Sciences

| volume=10 | at=id. 25 | date=February 2023

| doi=10.3389/fspas.2023.1064076 | doi-access=free

| bibcode=2023FrASS..1064076G }}

}}

{{refbegin}}

• {{citation

| last=Barbieri | first=C.

| title=Fundamentals of Astronomy | year=2006

| publisher=CRC Press | isbn=978-0-7503-0886-1 | page=253

| url = https://books.google.com/books?id=JhU6V1yDRCgC&pg=PA253 }}

• {{citation

| last=Billings | first=Charles E. | date=1973 | editor1-first=James F. | editor1-last=Parker | editor2-first=Vita R. | editor2-last=West | title=Bioastronautics Data Book | volume=3006 | edition=2nd | id=NASA SP-3006 | contribution=Barometric Pressure | bibcode=1973NASSP3006.....P }}

• {{citation

| last1=Bolonkin | first1=Alexander | title=Non-Rocket Space Launch and Flight | publisher=Elsevier | date=2010 | isbn=978-0-08-045875-5 | url=https://books.google.com/books?id=u-UqR8zIDEAC }}

• {{citation

| last1=Borowitz | first1=Sidney | last2=Beiser | first2=Arthur | date=1971 | title=Essentials of physics: a text for students of science and engineering | series=Addison-Wesley series in physics | edition=2nd | publisher=Addison-Wesley Publishing Company }} Note: this source gives a value of {{nowrap|2.7 × 10²⁵}} molecules per cubic meter.

• {{citation

| last1=Cajori | first1=Florian | date=1917 | title=A history of physics in its elementary branches: including the evolution of physical laboratories | location=New York | publisher=The Macmillan Company }}

• {{citation

| last1=Chamberlain | first1=Joseph Wyan | date=1978 | title=Theory of planetary atmospheres: an introduction to their physics and chemistry | volume=22 | series=International geophysics series | publisher=Academic Press | isbn=978-0-12-167250-8 | url=https://books.google.com/books?id=lt07vGeHkdMC&pg=PA2 }}

• {{citation | last1=Collins | first1=Martin J. | date=2007 | title=After Sputnik: 50 years of the Space Age | chapter=Mariner 2 Mock-up | publisher=HarperCollins | isbn=978-0-06-089781-9 | chapter-url=https://books.google.com/books?id=rZ53HRR5lUQC&pg=PA86 | url=https://archive.org/details/aftersputnik50ye00coll }}
• {{citation

| last1=Davies | first1=P. C. W. | date=1977 | title=The physics of time asymmetry | publisher=University of California Press | isbn=978-0-520-03247-7 }} Note: a light year is about 10¹³ km.

• {{citation

| last1=Davis | first1=Jeffrey R. | last2=Johnson | first2=Robert | last3=Stepanek | first3=Jan | title=Fundamentals of Aerospace Medicine | edition=4th | publisher=Lippincott Williams & Wilkins | date=2008 | isbn=978-0-7817-7466-6 | url = https://books.google.com/books?id=_6hymYAgC6MC&pg=PA270 }}

• {{citation

| title=A Dictionary of the Space Age

| series=New Series in NASA History

| first1=Paul | last1=Dickson | postscript=.

| publisher=JHU Press | year=2010 | isbn=978-0-8018-9504-3

| url = https://books.google.com/books?id=afKBvKlg0-EC&pg=PA57 }}

• {{citation

| last1=Eckert | first1=Michael | date=2006 | title=The dawn of fluid dynamics: a discipline between science and technology | publisher=Wiley-VCH | isbn=978-3-527-40513-8 }}

• {{citation

| last1=Ellery | first1=Alex | title=An introduction to space robotics | series=Springer-Praxis books in astronomy and space sciences | publisher=Springer | date=2000 | isbn=978-1-85233-164-1 | url=https://books.google.com/books?id=Sl8LggLa5R0C&pg=PA68 }}

• {{citation

| last1=Fichtner | first1=Horst | last2=Liu | first2=W. William | date=2011 | contribution=Advances in Coordinated Sun-Earth System Science Through Interdisciplinary Initiatives and International Programs | title=The Sun, the Solar Wind, and the Heliosphere | series=IAGA Special Sopron Book Series | editor1-first=M.P. | editor1-last=Miralles | editor2-first=J. Sánchez | editor2-last=Almeida | place=Sopron, Hungary | volume=4 | pages=341–345 | publication-place=Berlin | publisher=Springer | isbn=978-90-481-9786-6 | bibcode=2011sswh.book..341F | doi=10.1007/978-90-481-9787-3_24 }}

• {{citation | last1=Freedman | first1=Roger A. | last2=Kaufmann | first2=William J. | title=Universe | edition=7th| date=2005 | publisher=New York: W. H. Freeman and Company | isbn=978-0-7167-8694-8 }}
• {{citation

| last1=Frisch | first1=Priscilla C. | last2=Müller | first2=Hans R. | last3=Zank | first3=Gary P. | last4=Lopate | first4=C. | date=May 6–9, 2002 | contribution=Galactic environment of the Sun and stars: interstellar and interplanetary material | title=Astrophysics of life. Proceedings of the Space Telescope Science Institute Symposium | location=Baltimore, MD, US | editor1-first=Mario | editor1-last=Livio | editor2-first=I. Neill | editor2-last=Reid | editor3-first=William B. | editor3-last=Sparks | series=Space Telescope Science Institute symposium series | volume=16 | page=21 | publisher=Cambridge University Press | isbn=978-0-521-82490-3 | bibcode=2005asli.symp...21F }}

• {{citation

| last1=Gatti | first1=Hilary | date=2002 | title=Giordano Bruno and Renaissance science | publisher=Cornell University Press | isbn=978-0-8014-8785-9 }}

• {{citation

| last1=Genz | first1=Henning | date=2001 | title=Nothingness: the science of empty space | publisher=Da Capo Press | isbn=978-0-7382-0610-3 }}

• {{citation

| last1=Ghosh | first1=S. N. | date=2000 | title=Atmospheric Science and Environment | publisher=Allied Publishers | isbn=978-81-7764-043-4 | url=https://books.google.com/books?id=d6Azu3sfPAgC&pg=PA48 }}

• {{citation

| title=Space Weather & Telecommunications

| first=John M. | last=Goodman

| publisher=Springer Science & Business Media | year=2006

| url=https://books.google.com/books?id=4465qvHUZusC&pg=PA244|isbn=978-0-387-23671-1 }}

• {{citation

| last1=Grant | first1=Edward | date=1981 | title=Much ado about nothing: theories of space and vacuum from the Middle Ages to the scientific revolution | series=The Cambridge history of science series | publisher=Cambridge University Press | isbn=978-0-521-22983-8 | url=https://books.google.com/books?id=SidBQyFmgpsC&pg=PA10 }}

• {{citation

| last1=Hardesty | first1=Von | last2=Eisman | first2=Gene | last3=Krushchev | first3=Sergei | title=Epic Rivalry: The Inside Story of the Soviet and American Space Race | pages=89–90 | publisher=National Geographic Books | date=2008 | isbn=978-1-4262-0321-3 | url=https://books.google.com/books?id=kMQjbH8KAo0C&pg=PA90 }}

• {{citation

| last=Hariharan | first=P. | title=Optical interferometry | publisher=Academic Press | date=2003 | edition=2nd | isbn=978-0-12-311630-7 | url=https://books.google.com/books?id=EGdMO3rfVj4C }}

• {{citation

| last1=Harris | first1=Philip Robert | date=2008 | title=Space enterprise: living and working offworld in the 21st century | series=Springer Praxis Books / Space Exploration Series | publisher=Springer | isbn=978-0-387-77639-2 | url=https://books.google.com/books?id=b9RlRq_DP0UC&pg=PA68 }}

• {{citation

| last=Harrison | first=Albert A.| date=2002 | title=Spacefaring: The Human Dimension | publisher=University of California Press | isbn=978-0-520-23677-6 | url=https://books.google.com/books?id=vaFEIZMqLWgC&pg=PA60 }}

• {{citation

| last1=Holton | first1=Gerald James | last2=Brush | first2=Stephen G. | title=Physics, the human adventure: from Copernicus to Einstein and beyond | journal=Physics Today | volume=54 | issue=10 | page=69 | date=2001 | edition=3rd | publisher=Rutgers University Press | isbn=978-0-8135-2908-0 | url=https://books.google.com/books?id=czaGZzR0XOUC&pg=PA268 | bibcode=2001PhT....54j..69H | doi=10.1063/1.1420555 }}

• {{citation

| first1=Nick | last1=Kanas | first2=Dietrich | last2=Manzey

| title=Space Psychology and Psychiatry | chapter=Basic Issues of Human Adaptation to Space Flight | series=Space Technology Library

| date=2008 | volume= 22 | pages=15–48

| doi=10.1007/978-1-4020-6770-9_2 | postscript=.

| isbn=978-1-4020-6769-3 | bibcode=2008spp..book.....K }}

• {{citation

| last1=Kelly | first1=Suzanne | title=The de muno of William Gilbert | publisher=Menno Hertzberger & Co. | date=1965 | location=Amsterdam }}

• {{citation

| last1=Koskinen | first1=Hannu | date=2010 | title=Physics of Space Storms: From the Surface of the Sun to the Earth | series=Environmental Sciences Series | publisher=Springer | isbn=978-3-642-00310-3 | url=https://books.google.com/books?id=cO0nwfhXVjUC&pg=PA32}}

• {{citation

| last1=Lang | first1=Kenneth R. | date=1999 | title=Astrophysical formulae: Radiation, gas processes, and high energy astrophysics | series=Astronomy and astrophysics library | edition=3rd | publisher=Birkhäuser | isbn=978-3-540-29692-8 | url=https://books.google.com/books?id=HlGIXqzVEAgC&pg=PA462 }}

• {{citation

| first=Andrew | last=Liddle | date=2015

| publisher=John Wiley

| title=An Introduction to Modern Cosmology

| isbn=978-1-118-50214-3

| url=https://books.google.com/books?id=4lPWBgAAQBAJ&pg=PA33

}}

• {{citation

| last1=Lide | first1=David R. | date=1993 | title=CRC handbook of chemistry and physics | edition=74th | publisher=CRC Press | isbn=978-0-8493-0595-5 | url=https://books.google.com/books?id=q2qJId5TKOkC&pg=SA11-PA217 }}

• {{citation

| last1=Maor | first1=Eli | date=1991 | title=To infinity and beyond: a cultural history of the infinite | publisher=Princeton paperbacks | isbn=978-0-691-02511-7 }}

• {{citation

| last1=Mendillo | first1=Michael | contribution=The atmosphere of the moon | title=Earth-Moon Relationships | page=275 | location=Padova, Italy at the Accademia Galileiana Di Scienze Lettere Ed Arti | date=November 8–10, 2000 | editor1-first=Cesare | editor1-last=Barbieri | editor2-first=Francesca | editor2-last=Rampazzi | publisher=Springer | isbn=978-0-7923-7089-5 | url=https://books.google.com/books?id=vpVg1hGlVDUC&pg=PA275 }}

• {{citation

| last1=Needham | first1=Joseph | last2=Ronan | first2=Colin | title=The Shorter Science and Civilisation in China | volume=2 | publisher=Cambridge University Press | date=1985 | isbn=978-0-521-31536-4 }}

• {{citation

| last=O'Leary | first=Beth Laura | date=2009 | title=Handbook of space engineering, archaeology, and heritage | series=Advances in engineering | editor1-first=Ann Garrison | editor1-last=Darrin | publisher=CRC Press | isbn=978-1-4200-8431-3 | url=https://books.google.com/books?id=dTwIDun4MroC&pg=PA84 }}

• {{citation

| last1=Olenick | first1=Richard P. | last2=Apostol | first2=Tom M. | last3=Goodstein | first3=David L. | title=Beyond the mechanical universe: from electricity to modern physics | publisher=Cambridge University Press | date=1986 | isbn=978-0-521-30430-6 }}

• {{citation

| last1=Orloff | first1=Richard W. | title=Apollo by the Numbers: A Statistical Reference | publisher=NASA | date=2001 | access-date=2008-01-28 | isbn=978-0-16-050631-4 | url=https://history.nasa.gov/SP-4029/Apollo_08a_Summary.htm }}

• {{citation | last1=Papagiannis | first1=Michael D. | date=1972 | title=Space Physics and Space Astronomy | publisher=Taylor & Francis | isbn=978-0-677-04000-4 | url=https://archive.org/details/spacephysicsspac00mich }}
• {{Citation

| last1=Piantadosi | first1=Claude A. | title=The Biology of Human Survival: Life and Death in Extreme Environments | publisher=Oxford University Press | date=2003 | isbn=978-0-19-974807-5 | url=https://books.google.com/books?id=aeAg1X7afOoC&pg=PA63 }}

• {{citation

| last1=Porter | first1=Roy | last2=Park | first2=Katharine | last3=Daston | first3=Lorraine | title=The Cambridge History of Science: Early modern science | page=27 | work=Early Modern Science | volume=3 | publisher=Cambridge University Press | date=2006 | isbn=978-0-521-57244-6 }}

• {{citation

| last1=Prialnik | first1=Dina | title=An Introduction to the Theory of Stellar Structure and Evolution | publisher=Cambridge University Press | date=2000 | isbn=978-0-521-65937-6 | url=https://books.google.com/books?id=TGyzlVbgkiMC&pg=PA195 | access-date=2015-03-26 }}

• {{citation

| last1=Rauchfuss | first1=Horst | date=2008 | title=Chemical Evolution and the Origin of Life | others=Translated by T. N. Mitchell | publisher=Springer | url=https://books.google.com/books?id=aRkvNoDYtvEC&pg=PA72 | isbn=978-3-540-78822-5 }}

• {{Citation

| last1=Razani | first1=Mohammad | title=Information Communication and Space Technology | publisher=CRC Press | date=2012 | isbn=978-1-4398-4163-1 | url=https://books.google.com/books?id=cXZhGOKL7GIC&pg=PA98 }}

• {{citation

| last1=Schrijver | first1=Carolus J. |author-link2=George Siscoe | last2=Siscoe | first2=George L. | date=2010 | title=Heliophysics: Evolving Solar Activity and the Climates of Space and Earth | publisher=Cambridge University Press | isbn=978-0-521-11294-9 | url=https://books.google.com/books?id=M8NwTYEl0ngC&pg=PA363 }}

• {{citation

| last1=Silk | first1=Joseph | author-link1=Joseph Silk | date=2000 | title=The Big Bang | edition=3rd | publisher=Macmillan | isbn=978-0-8050-7256-3 }}

• {{citation | last1=Sparke | first1=Linda S.|author1-link=Linda Sparke | last2=Gallagher | first2=John S. | title= Galaxies in the Universe: An Introduction | edition=2nd | date=2007 | publisher=Cambridge University Press | bibcode=2007gitu.book.....S| isbn=978-0-521-85593-8 }}
• {{citation | last1=Spitzer | first1=Lyman Jr. | title=Physical Processes in the Interstellar Medium | date=1978 | publisher = Wiley Classics Library | isbn=978-0-471-29335-4 }}
• {{citation

| first=Emmeline Charlotte E. | last=Stuart Wortley | author-link=Emmeline Charlotte Elizabeth Stuart-Wortley | title=The maiden of Moscow, a poem | at=Canto X, section XIV, lines 14–15 | publisher=How and Parsons | date=1841 | url=http://xtf.lib.virginia.edu/xtf/view?docId=chadwyck_ep/uvaGenText/tei/chep_3.0980.xml | quote=All Earth in madness moved,—o'erthrown, / To outer space—driven—racked—undone! }}

• {{citation

| last1=Tassoul | first1=Jean Louis | last2=Tassoul | first2=Monique | title=A concise history of solar and stellar physics | publisher=Princeton University Press | date=2004 | isbn=978-0-691-11711-9 | url=https://books.google.com/books?id=nRtUait0qTgC&pg=PA22 }}

• {{citation

| last1=Thagard | first1=Paul | date=1992 | title=Conceptual revolutions | publisher=Princeton University Press | isbn=978-0-691-02490-5 }}

• {{citation

| last1=Tyson | first1=Neil deGrasse | author-link1=Neil deGrasse Tyson | last2=Goldsmith | first2=Donald | date=2004 | title=Origins: fourteen billion years of cosmic evolution | pages=114–115 | publisher=W. W. Norton & Company | isbn=978-0-393-05992-2 }}

• {{citation

| author=United States

| title=United States Code 2006 Edition Supplement V

| publisher=United States Government Printing Office

| location=Washington D. C. | page=536 | year=2016

| url=https://books.google.com/books?id=2U1qJioS68cC&pg=PA536 }}

• {{citation

| last1=Von Humboldt | first1=Alexander | author-link=Alexander von Humboldt | title=Cosmos: a survey of the general physical history of the Universe | date=1845 | publisher=Harper & Brothers Publishers | location=New York | url=https://books.google.com/books?id=KjZRAAAAYAAJ&q=outer+space&pg=PA39 | hdl=2027/nyp.33433071596906 | hdl-access=free }}

• {{citation

| last1=Webb | first1=Stephen | date=1999 | title=Measuring the universe: the cosmological distance ladder | publisher=Springer | isbn=978-1-85233-106-1 }}

• {{citation

| first1=Mark | last1=Williamson | publisher=IET | year=2006

| title=Spacecraft Technology: The Early Years | volume=33

| series=History and Management of Technology Series

| url = https://books.google.com/books?id=npI5NsFG8ngC&pg=PA97

| isbn=978-0-86341-553-1 }}

• {{citation

| last1=Wong | first1=Wilson | last2=Fergusson | first2=James Gordon | title=Military space power: a guide to the issues | series=Contemporary military, strategic, and security issues | publisher=ABC-CLIO | date=2010 | isbn=978-0-313-35680-3 | url = https://books.google.com/books?id=GFg5CqCojqQC&pg=PA16 }}

• {{citation

| first1=Bogdan | last1=Wszolek

| title=Progress in New Cosmologies: Beyond the Big Bang

| editor1-first=H. C. | editor1-last=Arp

| editor2-first=C. R. | editor2-last=Keys

| editor3-first=K. | editor3-last=Rudnicki

| publisher=Springer Science & Business Media

| chapter=Is there Matter in Voids?

| year=2013 | isbn=978-1-4899-1225-1

| chapter-url = https://books.google.com/books?id=JCMDCAAAQBAJ&pg=PA67 }}

{{refend}}

{{sister project links|voy=Space|v=Category:Astronomy|d=Q4169|n=Category:Space|s=Category:Astronomy|b=Category:Subject:Astronomy}}

{{Inspace}}

{{Molecules detected in outer space}}

{{Authority control}}

{{Portal bar|Astronomy|Stars|Spaceflight|Solar System}}

{{DEFAULTSORT:Outer Space}}

Category:Space plasmas

Category:Environments

Category:Vacuum