Mission Info

Hipparcos, High Precision Parallax Collecting Satellite was scientific satellite of the European Space Agency (ESA). It was the first devoted to precision astrometry- the accurate measurement of the positions of celestial objects on the sky. Hipparcos successfully observed the celestial sphere for 3.5 years and pinpointed the positions of more than one hundred thousand stars with high precision, and more than one million stars with lesser precision.

Calculations from observations generated the Hipparcos Catalogue of 118,218 stars. Using this data astronomers were also able to identify groups of stars that move along the same waves across the spiral arms of the Milky Way. In particular, they identified a small clump of extremely old stars that are still moving on very similar orbits – a fossil relict of one of our Galaxy's first building blocks. This was one of the first proofs that galaxies build up in a hierarchical way, through the merging of smaller structures into increasingly larger ones.