Andrew Claude de la Cherois Crommelin (6 February 1865 – 20 September 1939) was anastronomer of French andHuguenot descent who was born inCushendun,County Antrim, Ireland.^{[1][2][3][4][5]}He was educated in England atMarlborough College andTrinity College, Cambridge. After a spell teaching atLancing College he found permanent employment at theRoyal Greenwich Observatory in 1891.^[6][7] He joined theRoyal Astronomical Society in 1888 and was its president from 1929-1931. In 1895 he joined theBritish Astronomical Association and was president from 1904-1906 and directed itscomet section 1898-1901 and 1907-1938.^[8]

In 1910 for their studies ofHalley’s Comet Crommelin andPhilip Herbert Cowell jointly received thePrix Jules Janssen from theSociété astronomique de France.^[9][10] For this work they also received the Lindemann prize of theAstronomische Gesellschaft in Germany.^[11][12]

In 1914 Crommelin published an introductory book on astronomy “The Star World”.^[13]

Crommelin had four children, of whom two died in a climbing accident onPillar Rock, Ennerdale, in 1933.^[14] The de la Cherois line was succeeded through Crommelin's daughter Andrina. The authorMay Crommelin was one of Andrew’s cousins.

An expert on comets, his calculation of orbits of previously identified Comet Pons 1818 II, Comet Coggia-Winnecke 1873 VII, and CometForbes 1928 III in 1929, showed that these were one and the same periodic comet.^[15][16] It thus received the rather unwieldy name "CometPons-Coggia-Winnecke-Forbes". In 1948, he was posthumously honored when the comet was renamed after him alone (today, in modern nomenclature, it is designated27P/Crommelin). This is similar to the case ofComet Encke, where the periodic comet is named after the person who determined the orbit rather than the possibly-multiple discoverers and re-discoverers at each apparition. In 1937 Crommelin andMary Proctor jointly published a book entitled "Comets: Their Nature, Origin, and Place in the Science of Astronomy”.^[17]

Crommelin took part in severalsolar eclipse expeditions including those of1896,1900 and1905.^[18][19][20] In1919 he went toSobral, inBrazil, and measured the amount of deflection of light caused by thegravitational field of the Sun.^[21] The results from these observations were crucial in providing confirmation of theGeneral Theory of Relativity, whichAlbert Einstein had proposed in 1916.

• Comet27P/Crommelin
• Crommelin (lunar crater)
• Crommelin (Martian crater)
• Asteroid1899 Crommelin^[22]

• 1865 births
• 1939 deaths
• 19th-century British astronomers
• 20th-century British astronomers
• Alumni of Trinity College, Cambridge
• People educated at Marlborough College
• Presidents of the Royal Astronomical Society
• Recipients of the Lalande Prize
• People from Cushendun
• Scientists from County Antrim

• Articles with short description
• Short description is different from Wikidata
• Use dmy dates from September 2019