5 Astraea

From Wikipedia, the free encyclopedia

5 Astraea  
Discovery
Discovered by Karl Ludwig Hencke
Discovery date December 8, 1845
Designations
Alternative names 1969 SE
Minor planet
category
Main belt
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°
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 (geometric)[1]
Temperature ~167 K
max: 263 K (-10 °C)
Spectral type S-type asteroid
Apparent magnitude 8.7 to 12.92
Absolute magnitude 6.85
Angular diameter 0.15" to 0.041"

5 Astraea (pronounced /əˈstriːə/, 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).

Size comparison: the first 10 asteroids profiled against Earth's Moon. Astrea is the fifth from the left.
Size comparison: the first 10 asteroids profiled against Earth's Moon. Astrea is the fifth from the left.

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.[4] 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 Astrea proved to be the starting point for the eventual demotion of the four original asteroids (which were regarded as planets at the time)[4] 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
  1. ^ a b Supplemental IRAS Minor Planet Survey
  2. ^ a b c M. J. López-Gonzáles & E. Rodríguez Lightcurves and poles of seven asteroids, Planetary and Space Science, Vol. 53, p. 1147 (2005).
  3. ^ G. A. Krasinsky et al Hidden Mass in the Asteroid Belt, Icarus, Vol. 158, p. 98 (2002).
  4. ^ a b The Planet Hygea. spaceweather.com (1849). Retrieved on 2008-04-18.

[edit] External links