Born Berlin, (Germany), 13 August 1822
Died Copenhagen, Denmark, 14 June 1875
In addition to discovering three comets and 342 NGC objects, Heinrich d’Arrest assisted Johann Galle in discovering Neptune on 23 September 1846. D’Arrest studied mathematics and astronomy from 1839 at Berlin University. He was appointed second assistant observer at the Berlin Observatory in 1845; he left in 1848 to become an observer at the Leipzig Observatory. After earning his Ph.D. in 1850 at the University of Leipzig, he served there as extraordinary professor from 1852. In 1857, d’Arrest married Auguste Emilie Möbius, daughter of mathematician A. F. Möbius, under whom he worked at the observatory. That year, d’Arrest went to Copenhagen as professor of astronomy and director of the observatory there.
In 1845, Johann Encke , director of the Berlin Observatory, granted permission to search for the trans-Uranian planet whose location was predicted by Urbain Le Verrier that summer (and also independently by John Adams ). D’Arrest, still a graduate student, suggested to Galle that they make use of one of the unpublished Berliner Akademische Sternkartenproduced by Carl Bremiker . On the first night of searching, 23 September, Galle found an uncharted object, which became known first as Leverrier but soon as Neptune.
D’Arrest discovered comets C/1844 Y2, 6P/1851 M1, and C/1857 D1, all of which now bear his name; comet 6P/d’Arrest is a short-period comet that has been seen dated to 1678. He also studied properties of minor planets and discovered asteroid (76) Freia.
D’Arrest performed systematic observations of nebulae. In 1857, he published precise coordinates and descriptions of 269 such objects; in 1867, he published his observations of 1,942 nebulae. In 1873, d’Arrest, among the first to observe the spectra of nebulae, demonstrated that nebulae with bright emission lines (gaseous nebulae) lie mostly near the Milky Way.
D’Arrest was a corresponding member of the Saint Petersburg Academy and an associate of the Royal Astronomical Society of London, the Gold Medal of which he received in 1875. In addition to the three comets, his name has also been given to a lunar crater, a crater on the Martian satellite Phobos, and asteroid (13).