5 Astraea
 Basic size comparison between Astraea and dwarf planet Ceres. | |
| Discovery | |
|---|---|
| Discovered by | Karl Ludwig Hencke |
| Discovery date | December 8, 1845 |
| Designations | |
| Pronunciation | /æˈstriːə/ a-STREE-ə |
Named after | Astraea |
| 1969 SE | |
| Main belt | |
| Adjectives | Astraean |
| Symbol | .svg){kind=small} |
| Orbital characteristics | |
| Epoch November 26, 2005 (JD 2453700.5) | |
| Aphelion | 459.202 Gm (3.070 AU) |
| Perihelion | 310.688 Gm (2.077 AU) |
| 384.945 Gm (2.573 AU) | |
| Eccentricity | 0.193 |
| 1507.676 d (4.13 a) | |
Average orbital speed | 18.39 km/s |
| 194.442° | |
| Inclination | 5.369° |
| 141.690° | |
| 357.530° | |
| Proper orbital elements[1] | |
Proper semi-major axis | 2.5761849 AU |
Proper eccentricity | 0.1980486 |
Proper inclination | 4.5118628° |
Proper mean motion | 87.046396 deg / yr |
Proper orbital period | 4.13573 yr (1510.574 d) |
Precession of perihelion | 52.210903 arcsec / yr |
Precession of the ascending node | −57.357951 arcsec / yr |
| Physical characteristics | |
| Dimensions | 167×123×82 km[2][3] 119 km (mean) |
| Mass | 2.9×1018 kg[4][5] (assumed)[6] |
Mean density | ~3.3 g/cm³ |
| ~0.023 m/s² | |
| ~0.062 km/s | |
| 0.700 03 d (16.801 h)[3] | |
| Albedo | 0.227 (geometric)[2] |
| Temperature | ~167 K max: 263 K (-10 °C) |
Spectral type | S-type asteroid |
| 8.74 to 12.89 | |
| 6.85 | |
| 0.15" to 0.041" | |
5 Astraea is a large main-belt asteroid. Its surface is highly reflective (bright) and its composition is probably a mixture of nickel-iron with magnesium- and iron-silicates.
Astraea was the fifth asteroid discovered, on December 8, 1845, by K. L. Hencke and named for Astræa, a goddess of justice named after the stars. It was his first of two asteroid discoveries. The second was 6 Hebe. An amateur astronomer and post office employee, Hencke was looking for 4 Vesta when he stumbled on Astraea. The King of Prussia awarded him an annual pension of 1,200 marks for the discovery.[7]
Photometry indicates prograde rotation, that the north pole points in the direction of right ascension 9 h 52 min, declination 73° with a 5° uncertainty.[3] This gives an axial tilt of about 33°.
Astraea is physically unremarkable but notable mainly because for 38 years (after the discovery of Vesta in 1807) it had been thought that there were only four asteroids.[8] In terms of maximum brightness, it is indeed only the seventeenth brightest main-belt asteroid, being fainter than 192 Nausikaa and even, at rare near-perihelion oppositions, the highly eccentric carbonaceous 324 Bamberga.[1] It will be at magnitude +8.7 on a favorable opposition on February 15, 2016.
After the discovery of Astraea, thousands of other asteroids would follow. Indeed, the discovery of Astraea proved to be the starting point for the eventual demotion of the four original asteroids (which were regarded as planets at the time)[8] to their current status, as it became apparent that these four were only the largest of a whole new type of celestial body.
An occultation on 6 June 2008 produced an effective diameter (silhouette) of 115±6 km.[9]
Astraea has been studied by radar.[10] Arecibo observed Astraea in March 2012.[11][12]
References
- ^ "AstDyS-2 Astraea Synthetic Proper Orbital Elements". Department of Mathematics, University of Pisa, Italy. Retrieved 2011-10-01.
- ^ a b Supplemental IRAS Minor Planet Survey
- ^ a b c M. J. López-Gonzáles & E. Rodríguez Lightcurves and poles of seven asteroids, Planetary and Space Science, Vol. 53, p. 1147 (2005).
- ^ Michalak, G. (2001). "Determination of asteroid masses". Astronomy & Astrophysics. 374 (2): 703–711. Bibcode:2001A&A...374..703M. doi:10.1051/0004-6361:20010731. Retrieved 2008-11-10.
- ^ (Mass estimate of Astra 0.015 / Mass of Ceres 4.75) * Mass of Ceres 9.43E+20 = 2.977E+18
- ^ Michalak2001 (Table 6) assumed masses of perturbing asteroids used in calculations of perturbations of the test asteroids.
- ^ "Dawn Community". NASA. Archived from the original on 21 May 2009. Retrieved 2009-04-17.
{{cite web}}: Cite has empty unknown parameter:|coauthors=(help); Unknown parameter|deadurl=ignored (|url-status=suggested) (help) - ^ a b "The Planet Hygea". spaceweather.com. 1849. Archived from the original on 9 April 2008. Retrieved 2008-04-18.
{{cite web}}: Unknown parameter|deadurl=ignored (|url-status=suggested) (help) - ^ Ďurech, Josef; Kaasalainen, Mikko; Herald, David; Dunham, David; Timerson, Brad; Hanuš, Josef; Frappa, Eric; Talbot, John; Hayamizu, Tsutomu; Warner, Brian D.; Pilcher, Frederick; Galád, Adrián (2011). "Combining asteroid models derived by lightcurve inversion with asteroidal occultation silhouettes" (PDF). Icarus. 214 (2): 652–670. arXiv:1104.4227. Bibcode:2011Icar..214..652D. doi:10.1016/j.icarus.2011.03.016.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ "Radar-Detected Asteroids and Comets". NASA/JPL Asteroid Radar Research. Retrieved 2012-01-23.
- ^ Mike Nolan (2012-01-18). "Scheduled Arecibo Radar Asteroid Observations". Planetary Radar at Arecibo Observatory. Retrieved 2012-01-23.
- ^ http://www.naic.edu/~pradar/
