3 Juno

Juno was discovered on 1 September 1804, by Karl Ludwig Harding.{{cite book|title=Bode's Law and the Discovery of Juno|series=Historical Studies in Asteroid Research|publisher=Springer Publishing|chapter=The Discovery of Juno|last1=Cunningham|first1=Clifford J.|author-link=Clifford Cunningham|page=37|year=2017|isbn=978-3-319-32875-1|doi=10.1007/978-3-319-32875-1|bibcode=2017blsj.book.....C }} It was the third asteroid found, but was initially considered to be a planet; it was reclassified as an asteroid and minor planet during the 1850s.{{cite web | author=Hilton, James L. |title=When did the asteroids become minor planets? |work=U.S. Naval Observatory |url=http://aa.usno.navy.mil/faq/docs/minorplanets.php |access-date=2008-05-08 |archive-url = https://web.archive.org/web/20080324182332/http://aa.usno.navy.mil/faq/docs/minorplanets.php |archive-date = 2008-03-24}}

Juno is named after the mythological Juno, the highest Roman goddess. The adjectival form is Junonian (from Latin jūnōnius), with the historical final n of the name (still seen in the French form, Junon) reappearing, analogous to Pluto ~ Plutonian.

'Juno' is the international name for the asteroid, subject to local variation: Italian Giunone, French Junon, Russian Юнона (Yunona), etc.{{#tag:ref|There are two exceptions: Greek, where the name was translated to its Hellenic equivalent, Hera (3 Ήρα), as in the cases of 1 Ceres and 4 Vesta; and Chinese, where it is called the 'marriage-god(dess) star' (婚神星 hūnshénxīng). This contrasts with the goddess Juno, for which Chinese uses the transliterated Latin name (朱諾 zhūnuò).|group=lower-alpha}}

The old astronomical symbol of Juno, still used in astrology, is a scepter topped by a star, {{angbr|File:Juno symbol (fixed width).svg}}. There were many graphic variants with a more elaborated scepter, such as file:Juno orb symbol (fixed width).svg, sometimes tilted at an angle to provide more room for decoration.

The generic asteroid symbol of a disk with its discovery number, {{angbr|③}}, was introduced in 1852 and quickly became the norm.{{cite journal |last=Forbes |first=Eric G. |title=Gauss and the Discovery of Ceres |journal=Journal for the History of Astronomy |volume=2 |issue=3 |pages=195–199 |year=1971 |bibcode=1971JHA.....2..195F |doi=10.1177/002182867100200305 |s2cid=125888612 |url=http://adsabs.harvard.edu/full/1971JHA.....2..195F |access-date=18 July 2021 |archive-date=18 July 2021 |archive-url=https://web.archive.org/web/20210718200510/http://adsabs.harvard.edu/full/1971JHA.....2..195F |url-status=live }}{{cite journal |last=Gould |first=B. A. |author-link=Benjamin Apthorp Gould |title=On the symbolic notation of the asteroids |journal=Astronomical Journal |year=1852 |volume=2 |issue=34 |page=80 |bibcode=1852AJ......2...80G |doi=10.1086/100212 }} The scepter symbol was resurrected for astrological use in 1973.Eleanor Bach (1973) Ephemerides of the asteroids: Ceres, Pallas, Juno, Vesta, 1900–2000. Celestial Communications.

Juno is one of the larger asteroids, perhaps tenth by size and containing approximately 1% the mass of the entire asteroid belt.Pitjeva, E. V.; [http://journals.cambridge.org/production/action/cjoGetFulltext?fulltextid=303499 Precise determination of the motion of planets and some astronomical constants from modern observations] {{Webarchive|url=https://web.archive.org/web/20231214154827/https://www.cambridge.org/core/redirect-support |date=14 December 2023 }}, in Kurtz, D. W. (Ed.), Proceedings of IAU Colloquium No. 196: Transits of Venus: New Views of the Solar System and Galaxy, 2004 It is the second-most-massive S-type asteroid after 15 Eunomia. Even so, Juno has only 3% the mass of Ceres. The orbital period of Juno is 4.36578 years.{{cite web|title=Comets Asteroids |url=http://comets-asteroids.findthedata.org/l/3015/3-Juno |archive-url=https://archive.today/20140514074257/http://comets-asteroids.findthedata.org/l/3015/3-Juno |url-status=dead |archive-date=14 May 2014 |publisher=Find The Data.org |access-date=14 May 2014 }}

Amongst S-type asteroids, Juno is unusually reflective, which may be indicative of distinct surface properties. This high albedo explains its relatively high apparent magnitude for a small object not near the inner edge of the asteroid belt. Juno can reach +7.5 at a favourable opposition, which is brighter than Neptune or Titan, and is the reason for it being discovered before the larger asteroids Hygiea, Europa, Davida, and Interamnia. At most oppositions, however, Juno only reaches a magnitude of around +8.7

{{cite web

|title=The Brightest Asteroids

|publisher=The Jordanian Astronomical Society

|author=Odeh, Moh'd

|url=http://jas.org.jo/ast.html

|access-date=2008-05-21

|archive-url=https://web.archive.org/web/20080511115437/http://www.jas.org.jo/ast.html

|archive-date=11 May 2008

|url-status=dead

}}

—only just visible with binoculars—and at smaller elongations a {{convert|3|in|mm|adj=on}} telescope will be required to resolve it.

{{cite web|date=2004 |title=What Can I See Through My Scope? |publisher=Ballauer Observatory |url=http://www.allaboutastro.com/Articlepages/whatcanisee.html |access-date=2008-07-20 |url-status=dead |archive-url=https://web.archive.org/web/20110726123615/http://www.allaboutastro.com/Articlepages/whatcanisee.html |archive-date=26 July 2011 }} (archived)

It is the main body in the Juno family.

Juno was originally considered a planet, along with 1 Ceres, 2 Pallas, and 4 Vesta. In 1811, Schröter estimated Juno to be as large as 2290 km in diameter.

{{cite web

|date=2007-11-16

|author=Hilton, James L |author-link=James L. Hilton

|title=When did asteroids become minor planets?

|work=U.S. Naval Observatory

|url=http://aa.usno.navy.mil/faq/docs/minorplanets.php

|access-date=2008-06-22 |archive-url = https://web.archive.org/web/20080324182332/http://aa.usno.navy.mil/faq/docs/minorplanets.php |archive-date = 2008-03-24}}

All four were reclassified as asteroids as additional asteroids were discovered. Juno's small size and irregular shape preclude it from being designated a dwarf planet.

File:Moon_and_Asteroids_1_to_10.svg. Juno is third from the left.]]

Juno orbits at a slightly closer mean distance to the Sun than Ceres or Pallas. Its orbit is moderately inclined at around 12° to the ecliptic, but has an extreme eccentricity, greater than that of Pluto. This high eccentricity brings Juno closer to the Sun at perihelion than Vesta and further out at aphelion than Ceres. Juno had the most eccentric orbit of any known body until 33 Polyhymnia was discovered in 1854, and of asteroids over 200 km in diameter only 324 Bamberga has a more eccentric orbit.{{cite web|title=MBA Eccentricity Screen Capture |publisher=JPL Small-Body Database Search Engine |url=http://home.comcast.net/~kpheider/3Juno-ecc.jpg |access-date=2008-11-01 |url-status=dead |archive-url=https://web.archive.org/web/20090327111705/http://home.comcast.net/~kpheider/3Juno-ecc.jpg |archive-date=27 March 2009 }}

Juno rotates in a prograde direction with an axial tilt of approximately 50°.The north pole points towards ecliptic coordinates (β, λ) = (27°, 103°) within a 5° uncertainty.

{{cite journal | last= Kaasalainen | first= M. | author2= Torppa, J. | author3= Piironen, J. | title= Models of Twenty Asteroids from Photometric Data | journal= Icarus | volume= 159 | issue= 2 | pages= 369–395 | date= 2002 | url= http://www.rni.helsinki.fi/~mjk/IcarPIII.pdf | doi= 10.1006/icar.2002.6907 | bibcode= 2002Icar..159..369K | access-date= 30 November 2005 | archive-date= 16 February 2008 | archive-url= https://web.archive.org/web/20080216072340/http://www.rni.helsinki.fi/~mjk/IcarPIII.pdf | url-status= dead }} The maximum temperature on the surface, directly facing the Sun, was measured at about 293 K on 2 October 2001. Taking into account the heliocentric distance at the time, this gives an estimated maximum temperature of 301 K (+28 °C) at perihelion.

File:Juno orbit 2018.pngSpectroscopic studies of the Junonian surface permit the conclusion that Juno could be the progenitor of chondrites, a common type of stony meteorite composed of iron-bearing silicates such as olivine and pyroxene.

{{cite journal

| last= Gaffey

| first= Michael J.

|author2=Burbine, Thomas H.|author3=Piatek, Jennifer L.|author4=Reed, Kevin L.|author5=Chaky, Damon A.|author6=Bell, Jeffrey F.|author7= Brown, R. H.

| title= Mineralogical variations within the S-type asteroid class

| journal= Icarus | date= 1993 | volume= 106 | issue= 2 | page= 573

| bibcode= 1993Icar..106..573G | doi= 10.1006/icar.1993.1194}}

Infrared images reveal that Juno possesses an approximately 100 km-wide crater or ejecta feature, the result of a geologically young impact.

{{cite web

|title=Asteroid Juno Has A Bite Out Of It

|publisher=Harvard-Smithsonian Center for Astrophysics

|date=2003-08-06

|url=http://cfa-www.harvard.edu/press/pr0318.html

|access-date=2007-02-18

|archive-url=https://web.archive.org/web/20070208013152/http://cfa-www.harvard.edu/press/pr0318.html

|archive-date=8 February 2007

|url-status=dead

}}

{{cite journal

|last=Baliunas

|first=Sallie

|author2=Donahue, Robert

|author3=Rampino, Michael R.

|author4=Gaffey, Michael J.

|author5=Shelton, J. Christopher

|author6=Mohanty, Subhanjoy

|title=Multispectral analysis of asteroid 3 Juno taken with the 100-inch telescope at Mount Wilson Observatory

|journal=Icarus

|date=2003

|volume=163

|issue=1

|pages=135–141

|url=https://pubs.giss.nasa.gov/docs/2003/2003_Baliunas_ba04100j.pdf

|doi=10.1016/S0019-1035(03)00049-6

|bibcode=2003Icar..163..135B

|access-date=18 July 2017

|archive-date=23 January 2023

|archive-url=https://web.archive.org/web/20230123110931/https://pubs.giss.nasa.gov/docs/2003/2003_Baliunas_ba04100j.pdf

|url-status=live

}}

Based on MIDAS infrared data using the Hale Telescope, an average radius of 135.7 ± 11 km was reported in 2004.{{cite journal|doi=10.1016/j.icarus.2004.08.005|url=https://www.mit.edu/people/lucylim/2005_Icarus_LimMcConnochie_Thermal_infrared_8-13_micron_spectra.pdf|title=Thermal infrared (8?13 ?m) spectra of 29 asteroids: The Cornell Mid-Infrared Asteroid Spectroscopy (MIDAS) Survey|journal=Icarus|volume=173|issue=2|pages=385|year=2005|last1=Lim|first1=L|last2=McConnochie|first2=T|last3=Belliii|first3=J|last4=Hayward|first4=T|bibcode=2005Icar..173..385L|access-date=26 August 2019|archive-url=https://web.archive.org/web/20160303232808/http://www.mit.edu/people/lucylim/2005_Icarus_LimMcConnochie_Thermal_infrared_8-13_micron_spectra.pdf|archive-date=3 March 2016|url-status=dead}}

Juno was the first asteroid for which an occultation was observed. It passed in front of a dim star (SAO 112328) on 19 February 1958. Since then, several occultations by Juno have been observed, the most fruitful being the occultation of SAO 115946 on 11 December 1979, which was registered by 18 observers.{{cite journal

| display-authors= 8

| last= Millis

| first= R. L.

| author2= Wasserman, L. H.

| author3= Bowell, E.

| author4= Franz, O. G.

| author5= White, N. M.

| author6= Lockwood, G. W.

| author7= Nye, R.

| author8= Bertram, R.

| author9= Klemola, A.

| author10= Dunham, E.

| author11= Morrison, D.

| title= The diameter of Juno from its occultation of AG+0°1022

| journal= Astronomical Journal

| volume= 86

| pages= 306–313

| date= February 1981

| bibcode= 1981AJ.....86..306M

| doi= 10.1086/112889

| url= http://library2.smu.ca/bitstream/01/26050/1/Dupuy_David_L_article_1981.pdf

| access-date= 4 September 2019

| archive-date= 14 December 2023

| archive-url= https://web.archive.org/web/20231214154823/https://library2.smu.ca:443/bitstream/handle/01/26050/Dupuy_David_L_article_1981.pdf;jsessionid=FA53E7FF3F1BCDB4CC3B578960F38AB8?sequence=1

| url-status= live

}}

Juno occulted the magnitude 11.3 star PPMX 9823370 on 29 July 2013,[https://archive.today/20130729233004/http://www.asteroidoccultation.com/2013_07/0729_3_30531.htm Asteroid Occultation Updates – 29 Jul 2013] and 2UCAC 30446947 on 30 July 2013.[https://archive.today/20130729232944/http://www.asteroidoccultation.com/2013_07/0730_3_29995.htm Asteroid Occultation Updates – 30 Jul 2013].

Radio signals from spacecraft in orbit around Mars and on its surface have been used to estimate the mass of Juno from the tiny perturbations induced by it onto the motion of Mars.

{{cite conference

| first=E. V. | last= Pitjeva

| title= Estimations of masses of the largest asteroids and the main asteroid belt from ranging to planets, Mars orbiters and landers

| book-title= 35th COSPAR Scientific Assembly. Held 18–25 July 2004, in Paris, France

| pages= 2014 | date= 2004

| bibcode= 2004cosp...35.2014P}} Juno's orbit appears to have changed slightly around 1839, very likely due to perturbations from a passing asteroid, whose identity has not been determined.{{cite journal |last=Hilton |first=James L. |title=US Naval Observatory Ephemerides of the Largest Asteroids |journal=Astronomical Journal |volume=117 |issue=2 |pages=1077–1086 |date=February 1999 |doi=10.1086/300728 |bibcode=1999AJ....117.1077H |doi-access=free }}

In 1996, Juno was imaged by the Hooker Telescope at Mount Wilson Observatory at visible and near-IR wavelengths, using adaptive optics. The images spanned a whole rotation period and revealed an irregular shape and a dark albedo feature, interpreted as a fresh impact site.

File:Juno 4 wavelengths.jpg|Juno seen at four wavelengths with a large crater in the dark (Hooker telescope, 2003

File:Juno mpl anim.gif|Juno moving across background stars

File:3Juno-LB1-apmag.jpg|Juno during opposition in 2009

File:Animation of the asteroid Juno as imaged by ALMA.webm|Video of Juno taken as part of ALMA's Long Baseline Campaign

Juno reaches opposition from the Sun every 15.5 months or so, with its minimum distance varying greatly depending on whether it is near perihelion or aphelion. Sequences of favorable oppositions occur every 10th opposition, i.e. just over every 13 years. The last favorable oppositions were on 1 December 2005, at a distance of 1.063 AU, magnitude 7.55, and on 17 November 2018, at a minimum distance of 1.036 AU, magnitude 7.45.The Astronomical Almanac for the year 2018, G14[https://in-the-sky.org/news.php?id=20181116_14_100 Asteroid 3 Juno at opposition] {{Webarchive|url=https://web.archive.org/web/20171201031802/https://in-the-sky.org/news.php?id=20181116_14_100 |date=1 December 2017 }} 16 Nov 2018 at 11:31 UTC The next favorable opposition will be 30 October 2031, at a distance of 1.044 AU, magnitude 7.42.

• Juno clump
• List of former planets

{{notelist}}

{{reflist|refs=

{{cite web

|type=2017-11-26 last obs

|title=JPL Small-Body Database Browser: 3 Juno

|url=http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=3

|access-date=2014-11-17

|archive-date=5 January 2016

|archive-url=https://web.archive.org/web/20160105180053/http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=3

|url-status=live

}}

}}

{{Commons}}

• [http://ssd.jpl.nasa.gov/horizons.cgi?find_body=1&body_group=sb&sstr=3 JPL Ephemeris]
• [https://web.archive.org/web/20060627152558/http://www.cfa.harvard.edu/press/pr0318image.html Well resolved images from four angles] taken at Mount Wilson observatory
• [http://www.rni.helsinki.fi/~mjk/IcarPIII.pdf Shape model deduced from light curve]
• [http://www.jpl.nasa.gov/news/features.cfm?feature=2314 Asteroid Juno Grabs the Spotlight]
• {{cite web|title=Elements and Ephemeris for (3) Juno |publisher=Minor Planet Center |url=http://scully.cfa.harvard.edu/cgi-bin/returnprepeph.cgi?d=b2011&o=00003 |url-status=dead |archive-url=https://web.archive.org/web/20150904083927/http://scully.cfa.harvard.edu/cgi-bin/returnprepeph.cgi?d=b2011&o=00003 |archive-date=2015-09-04 }} (displays Elong from Sun and V mag for 2011)
• {{AstDys|3}}
• {{JPL small body}}

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Category:Juno asteroids

Juno

Juno

Category:Articles containing video clips

Category:S-type asteroids (Tholen)

Category:Sk-type asteroids (SMASS)

18040901

Category:Objects observed by stellar occultation

Category:Solar System