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# 11: Photographic Astrometry

Astrometry is the art and science of measuring positions of celestial objects, and indeed the first step in determining the orbit of a new asteroid or comet is to obtain a set of good astrometric positions. For much of the twentieth century, most astrometric positions were determined photographically.

Thumbnail: Motion of barycenter of solar system relative to the Sun. Carl Smith derivative work: Rubik-wuerfel