(c. 170 bc–c. 120 bc) Greek astronomer and geographer
Born at Nicaea, which is now in Turkey, Hipparchus (hi-par -kus) worked in Rhodes, where he built an observatory, and in Alexandria. None of his works has survived but many of them were recorded by Ptolemy. In 134 bc he observed a new star in the constellation of Scorpio. This led him to construct a catalog of about 850 stars. By comparing the position of the stars of his day with those given 150 years earlier he found that Spica, which was then 6° from the autumn equinox, had previously been 8°. He used this observation to deduce not the movement of Spica but the east to west precession (motion) of the equinoctial point. He calculated the rate of the precession as about 45 seconds of arc a year – a value close to the 50.27 seconds now accepted. He also introduced the practice of dividing the stars into different classes of magnitude based on their apparent brightness. The brightest stars he classed as first magnitude and those just visible to the naked eye he classed as sixth magnitude.
As a theorist Hipparchus worked on the orbits of the Sun and Moon. He established more accurate lengths of both the year and the month and was able to produce more accurate eclipse predictions. One of his lasting achievements was the construction of a table of chords, which virtually began the discipline of trigonometry. The concept of a sine had not yet been developed. Instead, Hipparchus calculated the ratio of the chord to the diameter of its own circle, which was divided into 120 parts. Thus if a chord produced by an angle of 60° is half the length of the radius, it would have, for Hipparchus, 60 parts. He much improved the geography of Eratosthenes, fixing the parallels astronomically.

Scientists. . 2011.

Look at other dictionaries:

  • Hipparchus — (Greek polytonic|Ἵππαρχος; ca. 190 BC ndash; ca. 120 BC) was a Greek astronomer, geographer, and mathematician of the Hellenistic period.Hipparchus was born in Nicaea (now Iznik, Turkey), and probably died on the island of Rhodes. He is known to… …   Wikipedia

  • Hipparchus — puede hacer referencia a: Hipparchus, astrónomo griego también conocido como Hiparco de Nicea. Hipparchus, cráter del planeta Marte. Hipparchus, cráter de La Luna. Esta página de desambiguación cataloga artículos relacionados con el mismo título …   Wikipedia Español

  • Hippárchus — Hippárchus, Sohn des Pisistratus, mit seinem Bruder Hippias (s.d.) Herrscher von Athen, 514 v. Chr. am Fest der Panathenäen aus Privatrache von Harmodius und Aristogiton ermordet …   Kleines Konversations-Lexikon

  • Hipparchus — [hi pär′kəs] 2d cent. B.C.; Gr. astronomer …   English World dictionary

  • Hipparchus — /hi pahr keuhs/, n. 1. died 514 B.C., tyrant of Athens 527 514. 2. c190 c125 B.C., Greek astronomer. * * * or Hipparchos born , Nicaea, Bithynia died after 127 BC, Rhodes? Greek astronomer and mathematician. He discovered the precession of the… …   Universalium

  • HIPPARCHUS — I. HIPPARCHUS Dux Atheniensium, coniurans contra Heraclidem Demetrii praesidem, Athenas frenantem; occisus ab eodem detectâ per Hieroclem coniuratione. Polyaen. l. 5. II. HIPPARCHUS Nicaeus Astrologus, scripsit de Arati Phaenomenis, de stellis… …   Hofmann J. Lexicon universale

  • Hipparchus — I. biographical name died 514 B.C. tyrant of Athens (527 514) II. biographical name or Hipparchos flourished 146 127 B.C. Greek astronomer …   New Collegiate Dictionary

  • Hipparchus — noun An ancient Greek astronomer, geographer, and mathematician …   Wiktionary

  • HIPPARCHUS —    ancient astronomer, born at Nicæa; flourished in the 2nd century B.C.; discovered among other things the precession of the equinoxes, determined the place of the equinox, and catalogued 1000 fixed stars …   The Nuttall Encyclopaedia

  • Hipparchus — Hip•par•chus [[t]hɪˈpɑr kəs[/t]] n. 1) anh big died 514 b.c., tyrant of Athens 527–514 2) big c190–c125 b.c., Greek astronomer …   From formal English to slang

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”