18 February 2020Astrometry Lost and Regained

Erik HOEG 
Niels Bohr Institute Copenhagen, Danemark

From an experiment in Copenhagen in 1925 to the Hipparcos and Gaia space missions. Astrophysicists need accurate positions, distances and motions of stars in order to understand the evolution of stars and the universe.Astrometry provides such information, but this old branch of astronomy seemed dull and old fashioned to most astronomers in the competition with astrophysics. In fact, astrometry was facing extinction during much of the 20^th century. The direction to go was shown by observations at the Copenhagen Observatory in 1925 with a new technique: photoelectric astrometry. Digital techniques were successfully introduced in photoelectric astrometry with an astrometric telescope at the Hamburg Observatory in the 1960s. This development paved the way for space technology as pioneered in France and implemented in the European satellite Hipparcos, launched in 1989. The new ESA satellite Gaia, a million times more powerful than Hipparcos is due for launch in 2013. Subject of the talk is this history of 100 years astrometry in which the speaker has been involved since 1954.