5 Astraea
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A light curve based 3D model of Astraea
|
|
| Discovery | |
|---|---|
| Discovered by | K. L. Hencke |
| Discovery date | December 8, 1845 |
| Designations | |
| MPC designation | (5) Astraea |
| Pronunciation | /æˈstriːə/ a-STREE-ə |
|
Named after
|
Astraea |
| 1969 SE | |
| Main belt | |
| Adjectives | Astraean |
| Orbital characteristics | |
| Epoch December 9, 2014 (JD 2457000.5) | |
| Aphelion | 3.065755252 AU (459.202 Gm) |
| Perihelion | 2.08186277 AU (310.688 Gm) |
| 2.573809012 AU (384.945 Gm) | |
| Eccentricity | 0.19113549 |
| 4.129264267 a (1508.213773 d) | |
|
Average orbital speed
|
18.39 km/s |
| 260.189542° | |
| Inclination | 5.368523° |
| 141.59556° | |
| 358.92898° | |
| Proper orbital elements | |
|
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 119 km (mean) |
| 48 300 km2 | |
| Volume | 882 000 km3 |
| Mass | 2.9×1018 kg (assumed) |
|
Mean density
|
~3.3 g/cm³ |
| ~0.023 m/s² | |
| ~0.062 km/s | |
| 0.700 03 d (16.801 h) | |
|
Equatorial rotation velocity
|
6.44 m/s |
| Albedo | 0.227 (geometric) |
| 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 asteroid from the asteroid belt. Its surface is highly reflective (bright) and its composition is probably a mixture of nickel–iron with silicates of magnesium and iron. It is a S-type object in the Tholen classification system.
Astraea was the fifth asteroid discovered, on 8 December 1845, by Karl Ludwig 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. A German amateur astronomer and post office headmaster, 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.
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. 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. With an apparent magnitude of 8.7 (on a favorable opposition on 15 February 2016), it is indeed only the seventeenth-brightest main-belt asteroid, and fainter than, for example, 192 Nausikaa or even 324 Bamberga (at rare near-perihelion oppositions).
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Wikipedia