The Hipparcos satellite: a dramatic improvement in our knowledge of the solar neighbourhood.

Abstract

Hipparcos was the first satellite to accurately measure angular displacements on the sky. Thanks to its original design, positions, trigonometric parallaxes and proper motions of unprecedented accuracy have been obtained for about 118000 stars and 50 objects in the solar system. The results cover a wide variety of subjects: reference systems, stellar physics and evolution, galactic kinematics, dynamics and evolution, distance and age scale in the Universe. In this first paper, a brief description of the Hipparcos mission, its main astrometric and photometric results, and the dramatic improvement in the authors understanding of the solar neighbourhood are presented.