Hipparchus
an ancient Greek astronomer; born in Nicæa, Bithynia. He lived about 160-125 в. c. He resided for some time at Rhodes, but afterward went to Alexandria, then the great school of science. A commentary on Aratus is the only work of his extant. He first ascertained the true length of the year, discovered the procession of the equinoxes, determined the revolutions and mean motions of the planets, prepared a catalogue of the fixed stars, etc.
HIPPIAS (hip'pi-as), tyrant of Athens. He was the son of Pisistratus, at whose death he assumed the government, in conjunction with his brother HIP- PARCHUS (q. v.), on whose death he seized the reins of government, and revenged the death of his brother by putting to death all of whom he entertained the least suspicion. His tyranny at last became so obnoxious to the citizens that he was expelled from the city 510 в. c.
He afterward induced Darius to apply to the Athenians in his favor; and their decisive refusal kindled the first war of the Persians against the European Greeks. According to some authorities he fell at Marathon, fighting against his countrymen, 490 в. c.