5 Astraea

Discovery
Discoverer	Karl Ludwig Hencke
Discovery Date	December 8, 1845
Alternate Designations	1969 SE
Category	Main belt
Orbital Elements Epoch July 14, 2004 (JD 2453200.5)
Eccentricity (e)	0.193
Semi-Major Axis (a)	384.877 Gm (2.573 AU)
Perihelion (q)	310.509 Gm (2.076 AU)
Aphelion (Q)	459.245 Gm (3.070 AU)
Orbital Period (P)	1507.279 d (4.13 a)
Mean Orbital Speed	18.57 km/s
Inclination (i)	5.370°
Longitude of the Ascending Node (Ω)	141.690°
Argument of Perihelion (ω)	357.536°
Mean Anomaly (M)	75.005°
Physical Characteristics
Dimensions	119.1 km
Mass	~1.8×1018 kg
Density	2 ? g/cm³
Surface Gravity	~0.033 m/s²
Escape Velocity	~0.063 km/s
Rotation Period	0.700 00 d1 (http://www.psi.edu/pds/archive/lc.html)
Spectral Class	S-type asteroid
Absolute Magnitude	6.85
Albedo	0.227 2 (http://dorothy.as.arizona.edu/DSN/IRAS/index_iras.html)
Mean Surface Temperature	~230 K

5 Astraea ("ass TRY aa"; written Astræa in the early scientific litterature) is a large Main belt asteroid. Its surface is highly reflective (bright) and the composition is probably a mixture of nickel-iron with magnesium- and iron-silicates.

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 $ (1968 dollars) for the discovery.

It is notable mainly because for 38 years (since 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.

There has been only one observed stellar occultation by Astraea (February 2, 1991).

External links

• AN 23 (1846) 393 (http://adsabs.harvard.edu//full/seri/AN.../0023//0000211.000.html) (in German)
• MNRAS 7 (1846) 27 (http://adsabs.harvard.edu//full/seri/MNRAS/0007//0000027.000.html)

The Minor Planets

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(For other objects and regions, see: Binary asteroids, Asteroid moons and the Solar system)

(For a complete listing, see: List of asteroids)

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