earthlight (astronomy)
{{Short description|Light reflected from the Earth}}
{{about|light reflected by Earth|light generated in Earth's atmosphere|Airglow|other uses|Earthlight (disambiguation)}}
{{redirect|Earthshine|the song by Rush|Vapor Trails}}
File:Aschgraues.Mondlicht.P1162513.jpg
Earthlight is the diffuse reflection of sunlight reflected from Earth's surface and clouds. Earthshine (an example of planetshine), also known as the Moon's ashen glow, is the dim illumination of the otherwise unilluminated portion of the Moon by this indirect sunlight. Earthlight on the Moon during the waxing crescent is called "the old Moon in the new Moon's arms",{{cite web |last1=Nemiroff |first1=Robert |last2=Bonnell |first2=Jerry |title=Old Moon in the New Moon's Arms |url=https://apod.nasa.gov/apod/ap180120.html |website=Astronomy Picture of the Day |publisher=NASA |date=20 January 2018 |access-date=11 January 2020 |archive-url=https://web.archive.org/web/20190617060044/https://apod.nasa.gov/apod/ap180120.html |archive-date=17 June 2019 |language=en}} while that during the waning crescent is called "the new Moon in the old Moon's arms".{{cite web |last1=Nemiroff |first1=Robert |last2=Bonnell |first2=Jerry |title=The New Moon in the Old Moon's Arms |url=https://apod.nasa.gov/apod/ap120324.html |website=Astronomy Picture of the Day |publisher=NASA |date=24 March 2012 |access-date=11 January 2020 |archive-url=https://web.archive.org/web/20190903235957/https://apod.nasa.gov/apod/ap120324.html |archive-date=3 September 2019 |language=en}}
Visibility
=At Earth=
Earthlight has a calculated maximum apparent magnitude of −17.7 as viewed from the Moon. When the Earth is at maximum phase, the total radiance at the lunar surface is approximately {{nowrap|0.15 W m−2}} from Earthlight. This is only 0.01% of the radiance from direct Sunlight.{{cite journal
| title=Earthshine as an illumination source at the Moon
| last1=Glenar | first1=David A. | last2=Stubbs | first2=Timothy J.
| last3=Schwieterman | first3=Edward W. | last4=Robinson | first4=Tyler D.
| last5=Livengood | first5=Timothy A. | display-authors=1
| journal=Icarus | volume=321 | pages=841–856
| date=March 2019 | doi=10.1016/j.icarus.2018.12.025
| arxiv=1904.00236 | bibcode=2019Icar..321..841G
| s2cid=90262609 }} Earthshine has a calculated maximum apparent magnitude of −3.69 as viewed from Earth.{{cite journal | last=Agrawal | first=Dulli Chandra | title=Apparent magnitude of earthshine: a simple calculation | journal=European Journal of Physics | publisher=IOP Publishing | volume=37 | issue=3 | date=2016-03-30 | issn=0143-0807 | doi=10.1088/0143-0807/37/3/035601 | page=035601| bibcode=2016EJPh...37c5601A | s2cid=124231299 }}
This phenomenon is most visible from Earth at night (or astronomical twilight) a few days before or after the day of new moon,{{cite book |url=https://books.google.com/books?id=sb44AQAAMAAJ&q=earthlight+best+observed+after+new+moon&pg=PA105 |title=The Eclectic Magazine of Foreign Literature, Science, and Art |date=1874 |publisher=Leavitt, Trow, & Company}} when the lunar phase is a thin crescent. On these nights, the entire lunar disk is both directly and indirectly sunlit, and is thus unevenly bright enough to see. Earthshine is most clearly seen after dusk during the waxing crescent (in the western sky) and before dawn during the waning crescent (in the eastern sky).
High contrast photography is also able to reveal the night side of the moon illuminated by Earthlight during a solar eclipse.Claro, Michael (October 2, 2019). "[https://www.space.com/total-solar-eclipse-2019-earthshine-photo.html Earthshine's Faint Illumination of the Moon Captured in Glorious Eclipse Photo]," Space.com. Retrieved 18 May 2023.
Radio frequency transmissions are also reflected by the moon; for example, see Earth–Moon–Earth communication.
=At the Moon=
The term earthlight would also be suitable for an observer on the Moon seeing Earth during the lunar night, or for an astronaut inside a spacecraft looking out the window.{{cite web |last1=Nemiroff |first1=Robert |last2=Bonnell |first2=Jerry |title=The Old Moon in the New Moon's Arms |url=https://apod.nasa.gov/apod/ap020419.html |website=Astronomy Picture of the Day |publisher=NASA |date=19 April 2002 |access-date=11 January 2020 |archive-url=https://web.archive.org/web/20190903214657/https://apod.nasa.gov/apod/ap020419.html |archive-date=3 September 2019 |language=en}} Arthur C. Clarke uses it in this sense in his 1955 novel Earthlight.
No person has been on the Moon during its night and experienced earthshine.
Earthshine is in the lunar night about 43 times brighter, and sometimes even 55 times brighter than a night on Earth illuminated by the light of the full moon.
Only on the far side and during lunar eclipses on the near side does the night become dark (and darker than a moonless night on Earth).{{cite web | last=Siegel | first=Ethan | title=Ask Ethan: How Bright Is The Earth As Seen From The Moon? | website=Forbes | date=March 18, 2017 | url=https://www.forbes.com/sites/startswithabang/2017/03/18/ask-ethan-how-bright-is-the-earth-as-seen-from-the-moon/ | access-date=April 29, 2025}}
Operations on the Moon and remote studying of the Moon and Earth is enabled by Earthlight, and has been used for research, for example to study Earth's environment by studying the amount of Earthlight it produces. Earthlight allows also some places on the surface of the lunar near side to be illuminated that are never illuminated by the Sun.{{cite journal | last=Glenar | first=David A. | last2=Stubbs | first2=Timothy J. | last3=Schwieterman | first3=Edward W. | last4=Robinson | first4=Tyler D. | last5=Livengood | first5=Timothy A. | title=Earthshine as an illumination source at the Moon | journal=Icarus | volume=321 | date=2019 | doi=10.1016/j.icarus.2018.12.025 | doi-access=free | pages=841–856 | url=https://arxiv.org/pdf/1904.00236 | access-date=April 29, 2025| arxiv=1904.00236 }}{{cite web | last=Plait | first=Phil | title=Earthshine Lights up the 'Dark Side' of the Moon | website=Scientific American | date=July 21, 2023 | url=https://www.scientificamerican.com/article/earthshine-lights-up-the-dark-side-of-the-moon/ | access-date=April 29, 2025}}
History
The phenomenon was sketchedda Vinci, Leonardo, "[https://www.sciencephoto.com/media/423155/view/moon-by-earthlight Moon by earthlight], Science Photo Library. Retrieved 18 May 2023. and remarked upon in the 16th century by Leonardo da Vinci, who thought that the illumination came from reflections from the Earth's oceans (we now know that clouds account for much more reflected intensity than the oceans).Carter, Jamie (May 15, 2023). "[https://www.livescience.com/space/the-moon/how-to-see-ghostly-da-vinci-glow-illuminate-the-crescent-moon-this-week How to see ghostly 'Da Vinci glow' illuminate the crescent moon this week],
Live Science. Retrieved 18 May 2023. This is why this phenomenon is sometimes called the Da Vinci Glow.{{Cite web |last=Kher |first=Aparna |date=March 10, 2025 |title=What is Earthshine? |url=https://www.timeanddate.com/astronomy/earthshine.html |url-status=live |access-date=March 10, 2025 |website=timeanddate}}
It is referenced in "The Ballad of Sir Patrick Spens" (Child Ballad No. 58), in the phrase "‘A saw the new muin late yestreen/ Wi the auld muin in her airm."Scottish anonymous (18th century or earlier; date uncertain). "Sir Patrick Spens," Scottish Poetry library. Retrieved 18 May 2023.
Astronaut Dr Sian Proctor was moved by seeing and experiencing earthlight from orbit as mission pilot of Inspiration4 space mission and wrote the poem, "Earthlight".{{cite web |last1=Proctor |first1=Sian |title=Earthlight by Astronaut Dr. Sian Proctor |url=https://www.youtube.com/watch?v=9xNjyLjUu8w&ab_channel=Dr.SianProctor |website=YouTube |publisher=Dr Sian Proctor |access-date=19 July 2024}} In 2024, Proctor authored EarthLight: The Power of EarthLight and the Human Perspective on the concept and nature of earthlight.
See also
References
{{Reflist}}
External links
- {{Commonscat-inline|Earthshine}}
{{The Moon}}