5 Astraea
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| Discovery | |
|---|---|
| Discovered by: | Karl Ludwig Hencke |
| Discovery date: | December 8, 1845 |
| Alternative names: | 1969 SE |
| Minor planet category: | Main belt |
| Orbital characteristics | |
| Epoch November 26, 2005 (JD 2453700.5) | |
| Aphelion distance: | 459.202 Gm (3.070 AU) |
| Perihelion distance: | 310.688 Gm (2.077 AU) |
| Semi-major axis: | 384.945 Gm (2.573 AU) |
| Eccentricity: | 0.193 |
| Orbital period: | 1507.676 d (4.13 a) |
| Avg. orbital speed: | 18.39 km/s |
| Mean anomaly: | 194.442° |
| Inclination: | 5.369° |
| Longitude of ascending node: | 141.690° |
| Argument of perihelion: | 357.530° |
| Physical characteristics | |
| Dimensions: | 167×123×82 km[1][2] |
| Mass: | ~2.4×1018 kg |
| Mean density: | ~2.7 g/cm³[3] |
| Equatorial surface gravity: | ~0.023 m/s² |
| Escape velocity: | ~0.062 km/s |
| Rotation period: | 0.700 03 d (16.801 h)[2] |
| Albedo: | 0.227[1] |
| Temperature: | ~167 K max: 263 K (-10 °C) |
| Spectral type: | S-type asteroid |
| Absolute magnitude: | 6.85 |
5 Astraea (IPA: [əˈstɹiə]; written Astræa in the early literature) 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. The adjectival form of the name, although unused, would be Astraean (which also designates a genus of star corals).
Astraea was the fifth asteroid discovered, on December 8, 1845 by K. L. Hencke. 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 with an annual pension of 300 US$ (1968 dollars) for the discovery.[citation needed]
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.[2] This gives an axial tilt of about 33°.
Astrea 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. After the discovery of Astraea, thousands of other asteroids would follow. Indeed, the discovery of Astrea 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.
There has been only one observed stellar occultation by Astraea (February 2, 1991).
[edit] References
- Yeomans, Donald K.. Horizons system. NASA JPL. Retrieved on 2007-03-20. — Horizons can be used to obtain a current ephemeris
- ^ 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).
- ^ G. A. Krasinsky et al Hidden Mass in the Asteroid Belt, Icarus, Vol. 158, p. 98 (2002).
[edit] External links
- AN 23 (1846) 393 (in German)
- MNRAS 7 (1846) 27
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|---|---|---|
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For a complete listing, see List of asteroids. See also Pronunciation of asteroid names and Meanings of asteroid names.
