Hipparcos


Hipparcos

▪ artificial satellite
in full  High Precision Parallax Collecting Satellite 
 Earth-orbiting satellite launched by the European Space Agency in 1989 that over the next four years measured the distances to more than 100,000 stars by direct triangulation using observations of parallax from either side of Earth's orbit around the Sun. It was named after the ancient Greek astronomer Hipparchus, who drew up an accurate star catalog in the 2nd century BC.

      Hipparcos got off to a rocky start when a rocket engine failed to insert the satellite into a circular geostationary orbit, leaving the satellite in a highly elliptical orbit that passed in and out of Earth's radiation belts (Van Allen radiation belt). It was nevertheless able to operate, and the computer analysis was modified to take the noncircularity of the orbit into account.

      As Hipparcos slowly rotated, a “split” Schmidt telescope continuously scanned the sky along two lines of sight 58° apart, and the manner in which the light from pairs of point sources impinged upon 2,688 very narrow parallel slits on the focal plane enabled angular separations to be precisely determined. By integrating observations, individual positions were computed to within 0.001 arc second—an improvement of 20 times over terrestrial estimates. The positions of 118,000 selected stars brighter than about 12th magnitude (roughly the observable limit for a 10-cm [4-inch] telescope) were thereby measured. Furthermore, observations taken years apart enabled the proper motions (proper motion) of these stars across the sky to be estimated.

      About 12,000 of the sampled stars proved to have variable brightness; three-quarters of these stars had not previously been suspected of being variable. Of particular interest were the Cepheid variables (Cepheid variable), whose period of variation is longer or shorter in direct proportion to their luminosity. Cepheid variables had been used as “standard candles” to measure the distances of nearby galaxies as the first step toward measuring the scale of the universe. Hipparcos refined the basis of this distance scale (galaxy). For example, observations from Hipparcos showed that M31 (the Andromeda Galaxy), the dominant member of the Local Group, to which the Milky Way Galaxy belongs, is actually 24 percent farther away from the Milky Way than had been previously believed. The recalibration of the Cepheid period-luminosity relationship also helped to refine the value of Hubble's constant, which measures the rate at which the universe is expanding.

David M. Harland
 

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Universalium. 2010.

Look at other dictionaries:

  • Hipparcos — Vue d artiste du satellite Hipparcos Caractéristiques Organisation ESA …   Wikipédia en Français

  • Hipparcos — Тестирование спутника в Large Solar Simulator, ESTEC Организация …   Википедия

  • Hipparcos — im Weltraum Hipparcos (High Precision Parallax Collecting Satellite) ist ein Satellit für Zwecke der Astrometrie. Er wurde nach dem griechischen Astronomen Hipparch von Nicäa benannt, der die Veränderlichkeit der Sternörter entdeckte …   Deutsch Wikipedia

  • Hipparcos — (The High Precision Parallax Collecting Satellite) fue un satélite astrométrico lanzado por la Agencia Espacial Europea (ESA) y dedicado a medir el paralaje y los movimientos propios de más de 2,5 millones de estrellas a menos de 150 pc de la… …   Wikipedia Español

  • Hipparcos — (The High Precision Parallax Collecting Satellite) fue un satélite astrométrico lanzado por la Agencia Espacial Europea (ESA) y dedicado a medir el paralaje y los movimientos propios de más de 2.5 millones de estrellas a menos de 150 pc de la… …   Enciclopedia Universal

  • Hipparcos — Infobox Space telescope name = Hipparcos caption = Artist s conception of Hipparcos in space organization = European Space Agency major contractors = alt names = nssdc id = location = orbit type = Geostationary transfer orbit height = 507 to… …   Wikipedia

  • Hipparcos — Hippạrcos   [Kurzbezeichnung für englisch high precision parallaxe collecting satellite; »Parallaxe(n) mit hoher Genauigkeit sammelnder Satellit«], 1989 gestarteter Astrometriesatellit der ESA, der bis 1993 der Datenübermittlung diente. Obwohl… …   Universal-Lexikon

  • HIPPARCOS — HIgh Precision PARallax COllecting Satellite (ESA) Astronomie …   Acronyms

  • HIPPARCOS — HIgh Precision PARallax COllecting Satellite (ESA) {Astronomie} …   Acronyms von A bis Z

  • HIPPARCOS — High Processor Parallax Collecting Satellite Contributor: GSFC …   NASA Acronyms


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