A light curve based 3D model of Astraea
|Discovered by||K. L. Hencke|
|Discovery date||December 8, 1845|
|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)|
|4.129264267 a (1508.213773 d)|
Average orbital speed
|Proper orbital elements|
Proper semi-major axis
Proper mean motion
|87.046396 deg / yr|
Proper orbital period
Precession of perihelion
|52.210903 arcsec / yr|
Precession of the ascending node
|−57.357951 arcsec / yr|
119 km (mean)
|48 300 km2|
|Volume||882 000 km3|
|0.700 03 d (16.801 h)|
Equatorial rotation velocity
max: 263 K (-10 °C)
|8.74 to 12.89|
|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.
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).
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) to their current status, as it became apparent that these four were only the largest of a whole new type of celestial body.
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- M. J. López-Gonzáles & E. Rodríguez Lightcurves and poles of seven asteroids, Planetary and Space Science, Vol. 53, p. 1147 (2005).
- Calculated based on the known parameters
- 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.[permanent dead link]
- (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.
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- "JPL Small-Body Database Browser: 5 Astraea
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