Edmond Halley in 1718 found that some stars had significantly moved from their ancient astrometric positions.
2.
Witt was taking a 2-hour exposure of Beta Aquarii to secure astrometric positions of asteroid 185 Eunike.
3.
A distinguished observer of comets and minor planets, he has determined exact astrometric positions from photographic plates for many thousands of small Solar System bodies.
4.
He was a very prolific minor planet-observer of both physical properties and astrometric positions, and had discovered more than 250 asteroids since 2002, most of them from the main-belt, as well as several near-Earth objects, Mars-crossers and Jupiter trojans.
5.
The principle of reconstructing space astrometric positions from one-dimensional observations carried out in the innovative Hipparcos sky scanning mode was fully original ( and frequently questioned outside the project ), and at the very limit of available computational power even by the end of the mission in 1997.
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