Hipparcos, the New Reduction of the Raw Data

Astrometry in the 1960s and 1970s was still entirely ground-based, and all too often seen (and experienced by very few) as a rather tedious, time-consuming technique that no longer could create much of an impact on the study of astrophysics. Parallax measurements seemed to have reached their limit and were hampered by calibration uncertainties, and proper motion studies were only in a few cases still breaking new ground. The maintenance of the optical reference frame, the Fundamental Katalog, was a lengthy process based on accumulating, cleaning and calibrating observations spread over two centuries. Most meridian telescopes were closed down and dismantled, the resulting space being used for library extensions, offices or a canteen. Limitations to measuring accuracy by the Earth's atmosphere, and the inability to observe all the sky with the same instrument under the same conditions made it difficult for astrometrists to improve significantly upon already achieved results. There remained a need, however, for improved astrometric data, and in particular for improvements in the quality and quantity of parallax measurements, to support ever more detailed astrophysical theories and models.