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Launch of the astrometric satellite Hipparcos

The exact determination of the positions and motions of stars is limited using ground-based instruments because of atmospheric turbulence. However, these measurements are extremely important for the study of the structure and evolution of our galaxy, the Milky Way. It is thus necessary to go into space. That is the purpose of the European project Hipparcos, piloted by the Observatory. Hipparcos was able to measure the positions of 100,000 stars with a precision of one-thousandth of a second of arc, revolutionizing the study of the Milky Way.

caption : The Hipparcos satellite - credits : Photo-ESA/Picture Report

To know more : Hipparcos, the first astrometric satellite