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(hi-par -koss) (High-Precision Parallax Collecting Satellite) An astrometric satellite of the European Space Agency (ESA) launched in Aug. 1989 to gather modern data on the position, brightness and other properties of an input catalog of selected stars with an unprecedented level of accuracy. Although its name was an acronym, it was deliberately chosen to recall the ancient Greek astronomer Hippachus, who compiled an important star catalog in the 2nd century BC. A faulty booster motor failed to lift Hipparcos into its intended geostationary orbit, but, following a revision of its mission, it was operated successfully from its 10-hour orbit and completed its mission in 4 years (rather than the planned 2.5 years). Prolonged exposure to radiation eventually caused it to cease working in 1993.

The satellite's 29-cm Schmidt telescope plotted very exactly the position, magnitude, parallax, and proper motion of a large number of stars. The resulting Hipparcos catalog (published 1997) gave the positions of 118 218 stars with a precision (0.002 arcsec) not possible from the ground. It was complete to magnitude 7.5 but included many fainter stars down to magnitude 12.5. The mean epoch was 1991.25. The less accurate Tycho catalog was prepared using the Hipparcos satellite's less sensitive star tracker instrument and was published the same year. Tycho gave positional date and magnitudes for the 1 058 332 brightest stars, including many as faint as magnitude 11.5. Tycho 2, a collaborative venture between the United States Navy Observatory and the University of Copenhagen, Denmark, was released on CD-ROM in 2000. It extended the number of the brightest stars listed to 2 539 913, complete to magnitude 11, with their positions precessed to J2000.0.

Among its other achievements, Hipparcos helped to forecast the impacts on Jupiter of the fragments of Comet Shoemaker-Levy 9 and identified stars that in the far future will pass close to the Sun.

References in periodicals archive ?
He continued that one of the things about the results by Hipparcos is that, in the case that they were right, the researchers do not really understand the physical parameters of the young stars.
My thought was to use the Hipparcos photometry as a tool to identify the most constant stars.
The main difference between EOC-3 and EOC-4 is that the latter was constructed with an improved procedure ensuring better consistency with Hipparcos and Tycho-2 positions at their mean epochs.
0 after reanalysis within the Hipparcos frame, Surveys in Geophysics 20, 169-195.
A further benefit is that the luminosity class of a star may be checked by using the Hipparcos parallax, combined with the observed magnitude.
Hipparcos became trapped in a highly irregular orbit when a rocket motor failed after it was brought up 300 mi from Earth by an Ariane rocket.
The new age estimate comes from new Hubble observations that pinned Methuselah's distance from Earth more precisely than previous estimates from the European Space Agency's Hipparcos satellite.
In the 1990s, the European Space Agency's star-mapping Hipparcos satellite determined the 434 light-year distance to Polaris, while other studies suggested the star could be closer to the sun.
Early estimates placed the cluster at an average of about 434 light-years away; then along came the European Space Agency's Hipparcos satellite, which found a distance of roughly 398 light-years by taking high-precision measurements of stellar motion and position.
I always check the possible comparisons with the Hipparcos catalogue (5) to ensure that it really is non-variable or has just a very small variation.
Hipparcos catalogue is highly accurate, however, cannot be effectively used in the vertical deflection measurements, as it contains too few star positions.
The availability of photometry from the Hipparcos satellite presents the opportunity to utilize a homogenous data set to calculate the Fourier parameters.