The satellite Hipparcos ( HIgh Precision Satellite PARallax COllecting , satellite of measurement of parallax with utmost precision) was a project of the European space agency dedicated to the measurement of the Parallaxe and own Mouvement of the star S. the satellite was used to measure the distance of more than 2,5 million stars located at less than 150 Parsec S of the Earth. The result holds into three catalogs of stars: the catalogs Hipparcos, Tycho and Tycho 2. The satellite was named in the honor of the Greek astronomer Hipparque, first to compile a star catalog.
The project was proposed in 1980. The satellite was launched the August 8th 1989 with 23:25 by a rocket ARIANE IV. The preliminary draft was to place it on a Geostationary orbit but a breakdown of one of the Booster S resulted in an elliptic orbit very. In spite of this problem, the majority of the scientific objectives were filled. The communications with the satellite were stopped the August 17th 1993.
The scientific program was composed of two parts:
- the experiment Hipparcos , of which the goal was to measure the five parameters astrometrical S of approximately 120 000 stars with a precision of about 2 to 4 milliseconds of arc.
- the experiment Tycho , of which the goal was to measure the astrometrical properties and photometric of 400 000 other stars but with a less precision.
The Catalog Hipparcos (120 000 stars with an accuracy of one millisecond of arc) and the Catalog Tycho (more than one million stars with an accuracy of 20-30 milliseconds of arc) were completed in August 1996 and published by the ESA in June 1997. The data of these catalogs were used to create the Millennium Star Atlas , an atlas covering the entirety of the sky and comprising a million stars until a Magnitude connects of 11 and supplemented by 10 000 not-stellar objects coming from other sources.
Tycho 2 , a new version of the Tycho catalog, was published in 2000. It is based on the same observations but, thanks to a method of more advanced data reduction, the data are slightly more precise there. This version is also much more complete: 2 539 913 stars are present there, which accounts for 99% of all stars until magnitude 11.
There exists a controversy about the data collected by the mission: an error of one millisecond arc could sully the results, at least in certain parts of the sky. For example, the value of the distance separating us from the Pléiades determined by Hipparcos is approximately 10% weaker than that determined by other methods. In 2004, the problem is still not solved (cf).
- Satellite Gaia
- the Hipparcos mission (in English)
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