5 Astraea (as-tree'-a; written Astrĉa 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).
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