8 August

1989:On 8 August 1989, ESA launched its Hipparcos mission. Hipparcos pinpointed the positions of one hundred thousand stars. It turned slowly on its axis and repeatedly scanned right around the sky on different slants.

Hipparcos measured angles between widely separated stars, and recorded their brightness, which were often variable from one visit to the next. Each star selected for study was visited about 100 times over four years.