Asteroid 5, the fifth asteroid to be discovered, by the German amateur astronomer Karl Ludwig Hencke (1793–1866) in 1845. Astraea is an S-type asteroid of diameter 120 km. Its orbit has a semimajor axis of 2.57 au, period 4.13 years, perihelion 2.08 au, aphelion 3.07 au, and inclination 5°.4.