Crommelin, Andrew Claude De Lacherois

(b. Cushendun, Northern Ireland, 6 February 1865; d. London, London, England, 20 September 1939)

astronomy

A member of a prominent Huguenot family, Crommelin was educated at Marlborough College and Trinity College, Cambridge, graduating in 1886. From 1891 to 1927 he was additional assistant at the Royal Observatory, Greenwich. He was president of the Royal Astronomical Society during 1929–1931 and of the British Astronomical Association during 1904–1906; he received the latter’s Goodacre Medal in 1937.

At Greenwich, Crommelin worked as both observer and computer. He made an accurate determination of the lunar parallax (1911) and prepared the physical ephemerides of the moon and outer planets (1897–1906). His photographs of the Brazilian solar eclipse (1919) helped to establish the relativistic deflection of light.

Crommelin’s principal contribution to science, however, involved comets and minor planets. In 1907–1908 he and Cowell traced back the motion of Halley’s comet to 240 b.c., identifying observations at almost every perihelion passage. They developed a direct method for studying the very complicated orbit of Jupiter’s eighth satellite, the equations being integrated by mechanical quadrature. They also applied the procedure to Halley’s comet, due to return in 1910, and for their exact result were awarded the Lindemann Prize of the Astronomische Gesellschaft and honorary D. Sc. degrees from Oxford University. Their predicted perihelion time was three days too early, and their suggestion that the error was due mainly to nongravitational forces has now been confirmed.

From 1891 to 1937 Crommelin wrote the annual reports on minor planets in the Monthly Notices of the Royal Astronomical Society and from 1916 the reports on comets as well. He calculated preliminary orbits for many comets, and it is directly due to his indefatigable efforts in providing predictions for the periodic comets that many of these objects have not become lost. From 1935 until his death he was president of the International Astronomical Union’s subcommission on periodic comets. He also served as director of the Comet Section of the British Astronomical Association (1897–1901, 1907–1939) and in this capacity produced sequels to Galle’s catalogs of cometary orbits. After his retirement from Greenwich he edited the Circulars of the association; and the association’s Journal and Handbook, as well as The Observatory, Nature, Knowledge, and the Circulars of the International Astronomical Union, contain innumerable notes by Crommelin concerning comets, minor planets, and other topics.

In 1929 Crommelin demonstrated that comet Forbes 1928 III was identical with comet Coggia-Winnecke 1873 VII and comet Pons 1818 I, the revolution period being twenty-eight years. He later showed that a comet seen in 1457 was probably (and one in 1625 possibly) the same object. In 1948 the International Astronomical Union changed the name of the comet from Pons-Coggia-Winnecke-Forbes to Crommelin (only the fourth occasion on which a comet has been named after the computer of its orbit, rather than its discoverer), and in 1956 the comet returned to perihelion just four days later than Crommelin had predicted.

BIBLIOGRAPHY

Some of Crommelin’s writings are “Essay on the Return of Halley’s Comet,” Publikation der Astronomichen Gesellschaft, no. 23 (1910), written with P. H. Cowell; “Comet Catalogue,” Memoirs of the British Astronomical Association, 26 , pt. 2 (1925), continued ibid., 30 , pt. 1 (1932); “Tables for Facilitating the Computation of the Perturbations of Periodic Comets by the Planets,” in Memoirs of the Royal Astronomical Society, 64 (1929), 149–207; and Comets (London, 1937), written with Mary Proctor.

An obituary notice is C. R. Davidson, Monthly Notices of the Royal Astronomical Society, 100 (1940), 234–236.

Brian G. Marsden