Basic size comparison between Astraea and dwarf planet Ceres.
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Discovery
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| Discovered by | Karl Ludwig Hencke |
| Discovery date | December 8, 1845 |
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Designations
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| Alternate name | 1969 SE |
| Minor planet category |
Main belt |
| Adjective | Astraean |
| Epoch November 26, 2005 (JD 2453700.5) | |
| Aphelion | 459.202 Gm (3.070 AU) |
| Perihelion | 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) |
| Average orbital speed | 18.39 km/s |
| Mean anomaly | 194.442° |
| Inclination | 5.369° |
| Longitude of ascending node | 141.690° |
| Argument of perihelion | 357.530° |
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Physical characteristics
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| Dimensions | 167×123×82 km[1][2] 119 km (mean) |
| Mass | 2.9 × 1018 kg[3][4] (assumed)[5] |
| Mean density | ~3.3 g/cm³ |
| 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 (geometric)[1] |
| Temperature | ~167 K max: 263 K (-10 °C) |
| Spectral type | S-type asteroid |
| Apparent magnitude | 8.7 to 12.92 |
| Absolute magnitude (H) | 6.85 |
| Angular diameter | 0.15" to 0.041" |
5 Astraea (pronounced /əˈstriːə/,[6] or as Greek: Αστραία; 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 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.[2] 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].
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.
There has been only one observed stellar occultation by Astraea (February 2, 1991).
References
- Yeomans, Donald K.. "Horizons system". NASA JPL. http://ssd.jpl.nasa.gov/?horizons. 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).
- ^ Michalak, G. (2001). "Determination of asteroid masses". Astronomy & Astrophysics 374: 703-711. doi:. http://www.aanda.org/index.php?option=article&access=standard&Itemid=129&url=/articles/aa/abs/2001/29/aa10228/aa10228.html. Retrieved on 2008-11-10.
- ^ (Mass estimate of Astra 0.015 / Mass of Ceres 4.75) * Mass of Ceres 9.43E+20 = 2.977E+18
- ^ Michalak2001 assumed masses of perturbing asteroids used in calculations of perturbations of the test asteroids.
- ^ In US dictionary transcription, us dict: ə·strē′·ə.
- ^ "Dawn Community". NASA. http://dawn.jpl.nasa.gov/DawnCommunity/flashbacks/fb_09.asp. Retrieved on 2009-04-17.
- ^ a b "The Planet Hygea". spaceweather.com. 1849. http://spaceweather.com/swpod2006/13sep06/Pollock1.jpg. Retrieved on 2008-04-18.
External links
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