* Astronomy

Blobrana · L

RE: Hipparcos mission

Blobrana · L

The most accurate catalogue of the distances to more than 100,000 stars has just been released.
Cambridge astronomer Dr Floor van Leeuwen has spent the past 10 years checking and recalculating data gathered by the Hipparcos satellite.
It collected the information in the 1990s, but questions were raised about apparent errors in the results.
Dr van Leeuwen, who saw a flaw in the way Hipparcos worked, has now corrected the star distances.

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Blobrana · L

It has been ten years since the release of the Hipparcos and Tycho catalogues, the first astrometric catalogues produced from observations in space. The Hipparcos catalogue has since been re-processed and fine-tuned, providing the best map of our galaxy to date.
ESAs Hipparcos (High Precision Parallax Collecting Satellite), launched in 1989, was the first, and so far only, space-based astrometry mission. Designed to determine the position and distance of more than 100 000 stars, its accuracy exceeded ground-based observations by a factor of 10 to 100. The mission also collected data on the proper motion and variability of stars and identified multiple star systems.
Hipparcos was managed and run exclusively by ESA and a consortium of European scientists. It resulted in the Hipparcos and Tycho catalogues which were first published in 1997. The catalogues provide information fundamental to all subjects in astronomy and remain unrivalled to this day.
The Hipparcos catalogue contains about 120 000 stars and can be used to study not only individual stars, but also the behaviour of stellar groups as well as the formation of our galaxy. The Tycho catalogue, an unplanned product of the mission, is a bigger source for the study of stars (about one million stars) and its data is also used for orientation of satellites in space.

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Blobrana · L

ESA's Hipparcos mission provided astrometric data on thousands of stars. Thanks to advances in computational processing power it has been possible to revisit the original data and improve the accuracy of the derived catalogue.
The accuracy of a data set, such as the Hipparcos astrometric data, is generally determined by two contributions: intrinsic, random, noise and modelling noise. The latter represents contributions from inaccuracies in the models used to calibrate and reduce the data. In the original Hipparcos catalogue published in 1997, the noise on the data for all stars brighter than about magnitude 9 is to some extent dominated by modelling noise. This noise contribution originated from the difficulty in reconstructing the reference frame with respect to the orientation and rotation rates of the satellite. Such modelling errors, unfortunately, also tend to produce errors that are correlated between neighbouring measurements, so that results become rather uncertain when combining data - as in the case of stars in a cluster.

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