| 词条 | 7 Iris |
| 释义 |
| minorplanet = yes | background=#D6D6D6 | name=7 Iris | symbol= | image = 7Iris-LB1-richfield-mag10.jpg | image_size = 240px | caption = Star rich field showing asteroid Iris (apmag 10.1) | discoverer=John Russell Hind | discovered=August 13, 1847 | pronounced ={{IPAc-en|ˈ|aɪər|ᵻ|s}} {{Respell|IRE|iss}} | mpc_name=(7) Iris | alt_names=none | adjectives=Iridian {{IPAc-en|aɪ|ˈ|r|ɪ|d|i|ə|n}}[1] | named_after = Īris | mp_category=Main belt | epoch=November 26, 2005 (JD 2453700.5) | semimajor=2.385 AU (356.798 Gm) | perihelion=1.833 AU (274.259 Gm) | aphelion=2.937 AU (439.337 Gm) | eccentricity=0.231 | period=3.68 a (1345.375 d) | inclination=5.527° | asc_node=259.727° | arg_peri=145.440° | mean_anomaly=269.531° | avg_speed=19.03 km/s | p_orbit_ref = [2] | p_semimajor = 2.3862106 | p_eccentricity = 0.2125516 | p_inclination = 6.3924857° | p_mean_motion = 97.653672 | perihelion_rate = 38.403324 | node_rate = −46.447128 | dimensions=240×200×200 km[3] 225×190×190 km[3] 199.8 ± 10 km (IRAS)[4] | surface_area=135 000 km2[5] | volume=4 630 000 km3[5] | mass=1.62 ± 0.09 {{e|19}} kg[6] | density=3.21 ± 0.49 g/cm³[6] | surface_grav={{Gr|0.0162|100|3}} m/s² | escape_velocity={{V2|0.0162|100|3}} km/s | rotation=0.2975 d[7] | rot_velocity=25.4 m/s[5] | spectral_type=S-type asteroid | magnitude = 6.7[8][9] to 11.4 | abs_magnitude=5.51 | albedo=0.277 | angular_size = 0.32" to 0.07" | single_temperature=~171 K max: 275 K (+2°C) }} Iris (minor planet designation: 7 Iris) is a large main-belt asteroid orbiting the Sun between Mars and Jupiter. It is the fourth-brightest object in the asteroid belt. It is classified as an S-type asteroid, meaning that it has a stony composition. Discovery and nameIris was discovered on August 13, 1847, by J. R. Hind from London, UK. It was Hind's first asteroid discovery and the seventh asteroid to be discovered overall. Iris was named after the rainbow goddess Iris in Greek mythology, who was a messenger to the gods, especially Hera. Her quality of attendant of Hera was particularly appropriate to the circumstances of discovery, as Iris was spotted following 3 Juno by less than an hour of right ascension (Juno is the Roman equivalent of Hera). CharacteristicsGeologyIris is an S-type asteroid. Its surface likely exhibits albedo differences, with possibly a large bright area in the northern hemisphere.[10] Overall the surface is very bright and is probably a mixture nickel-iron metals and magnesium- and iron-silicates. Its spectrum is similar to that of L and LL chondrites with corrections for space weathering,[11] so it may be an important contributor of these meteorites. Planetary dynamics also indicates that it should be a significant source of meteorites.[12] Among the S-type asteroids, Iris ranks fifth in geometric mean diameter after Eunomia, Juno, Amphitrite and Herculina. BrightnessIris's bright surface and small distance from the Sun make it the fourth-brightest object in the asteroid belt after Vesta, Ceres, and Pallas. It has a mean opposition magnitude of +7.8, comparable to that of Neptune, and can easily be seen with binoculars at most oppositions. At typical oppositions it marginally outshines the larger though darker Pallas.[13] But at rare oppositions near perihelion Iris can reach a magnitude of +6.7 (next time on October 31, 2017 reaching a magnitude of +6.9),[8] which is as bright as Ceres ever gets. RotationLightcurve analysis indicates a somewhat angular shape and that Iris's pole points towards the ecliptic coordinates (β, λ) = (10°, 20°) with a 10° uncertainty.[3] This gives an axial tilt of 85°, so that on almost a whole hemisphere of Iris, the sun does not set during summer, and does not rise during winter. On an airless body this gives rise to very large temperature differences. ObservationsIris was observed occulting a star on May 26, 1995, and later on July 25, 1997. Both observations gave a diameter of about 200 km. See also
References1. ^Oxford English Dictionary 2. ^{{cite web |title=AstDyS-2 Iris Synthetic Proper Orbital Elements |publisher=Department of Mathematics, University of Pisa, Italy |url=http://hamilton.dm.unipi.it/astdys/index.php?pc=1.1.6&n=7 |accessdate=2011-10-01 }} 3. ^1 {{cite journal| url=http://www.rni.helsinki.fi/~mjk/IcarPIII.pdf| first= M.| last= Kaasalainen| title=Models of twenty asteroids from photometric data| journal= Icarus| volume= 159| issue=2| pages= 369| date=2002| doi=10.1006/icar.2002.6907| bibcode=2002Icar..159..369K|display-authors=etal}} 4. ^{{cite web |date=2009-03-17 |quote=last obs |title=JPL Small-Body Database Browser: 7 Iris |url=http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=7 |accessdate=2009-03-17}} 5. ^1 2 Calculated based on the known parameters 6. ^1 2 {{cite web |date=2011 |title=Recent Asteroid Mass Determinations |publisher=Personal Website |author=Jim Baer |url=http://home.earthlink.net/~jimbaer1/astmass.txt |accessdate=2011-09-14}} 7. ^{{cite web|url=http://www.psi.edu/pds/archive/lc.html |title=Planetary Data System Small Bodies Node, lightcurve parameters |deadurl=yes |archiveurl=https://web.archive.org/web/20060614093519/http://www.psi.edu/pds/archive/lc.html |archivedate=2006-06-14 |df= }} 8. ^1 {{cite book| author=Donald H. Menzel| author2=Jay M. Pasachoff| last-author-amp=yes| date=1983| title=A Field Guide to the Stars and Planets| edition=2nd| publisher=Houghton Mifflin| pages=391| location=Boston, MA| isbn=0-395-34835-8 }} 9. ^{{cite web |title=Bright Minor Planets 2006 |publisher=Minor Planet Center |url=http://www.cfa.harvard.edu/iau/Ephemerides/Bright/2006 |accessdate=2008-05-21}} 10. ^{{cite journal| bibcode=1993A&AS..101..621H| first1=M.| last1= Hoffmann|author2= E. H. Geyer| title=Spots on 4-VESTA and 7-IRIS - Large Areas or Little Patches| journal= Astronomy and Astrophysics Supplement | volume= 101| pages= 621| date=1993}} 11. ^Y. Ueda et al. Surface Material Analysis of the S-type Asteroids: Removing the Space Weathering Effect from Reflectance Spectrum, 34th Annual Lunar and Planetary Science Conference, March 17–21, 2003, League City, Texas, abstract no.2078 (2003). 12. ^{{cite journal| bibcode=1997A&A...321..652M| first1= F.|last1= Migliorini| title=(7) Iris: a possible source of ordinary chondrites?| journal=Astronomy & Astrophysics| volume= 321| pages=652| date=1997| first2=A.|last2=Manara|first3=A.| last3=Cellino|first4=M.| last4=Di Martino|first5=V.| last5=Zappala|display-authors=1}} 13. ^{{cite web|last=Odeh |first=Moh'd |url=http://jas.org.jo/ast.html |title=The Brightest Asteroids |publisher=Jordanian Astronomical Society |accessdate=2007-07-16 |archiveurl=https://web.archive.org/web/20070813224051/http://www.jas.org.jo/ast.html |archivedate=13 August 2007 |deadurl=yes |df= }} External links
7 : Background asteroids|Discoveries by John Hind|Minor planets named from Greek mythology|Named minor planets|S-type asteroids (Tholen)|S-type asteroids (SMASS)|Astronomical objects discovered in 1847 |
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