Hipparchus (c. 190 - c. 120 B.C.)

Hipparchus or Hipparchos of Nicaea did his observations from Rhodes between 146 and 127 BC. He was the first astronomer who compiled a catalog of 850 stars; this work was perhaps triggered by the observation of a "New Star" (Nova) in the constellation Scorpius in 134 BC (according to Roman historian Pliny). He included two "nebulous objects" in his catalog, the Praesepe star cluster (M44, NGC 2632) and the Double Star Cluster in Perseus, h+chi Persei (NGC 869+884); Praesepe had been described earlier by Aratos.

By comparing his observations with earlier observers, in particular Timocharis and Aristyllus of Alexandria (c. 280 B.C.), Hipparchus discovered the precession of equinoxes. To remarkable acuracy, he obtained measurements of the value of precession, the length of the year, and (from eclipse observations) the distance of the Moon.

Hipparchus is commemorated by the naming of Moon Crater Hipparchus (5.1S, 5.2E, 138 km diameter, officially named in 1935), Mars Crater Hipparchus (44.8S, 151.4W, 93 km, in 1973), asteroid (4000) Hipparchus (discovered January 4, 1989 by S. Ueda and H. Kaneda in Kushiro, provisionally named 1989 AV and, on various pre-discovery sightings, 1963 XA, 1975 TW4, 1977 FZ2, 1978 NG8, 1979 WU4, 1984 YX5 and 1987 SD18), as well as ESA's astrometric satellite Hipparcos.

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