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Andrew Claude de la Cherois Crommelin
(1865 – 1939)
Andrew Claude de la Cherois Crommelin [Feb. 6, 1865 - Sept. 20, 1939] was a British astronomer, one of the world's greatest authorities on comets. Crommelin was born in Cushendun in County Antrim, Northern Ireland. He was educated in England at Marlborough College and Trinity College, the University of Cambridge, graduating in 1886. On leaving Cambridge, Crommelin became a member of the staff of Lancing College and, in 1891, was appointed assistant at the Royal Greenwich Observatory, where he became interested in the orbits of comets and minor planets.
An expert on comets, his calculation of orbits of what were then called Comet Forbes 1928 III, Comet Coggia-Winnecke 1873 VII, and Comet Pons 1818 II, in 1929, showed that these comets were one and the same periodic comet. The comet thus received the rather unwieldy name "Comet Pons-Coggia-Winnecke-Forbes". In 1948, he was posthumously honored when the comet was renamed after him alone (today, in modern nomenclature, it is designated 27P/Crommelin). This is similar to the case of Comet Encke, where the periodic comet is named after the person determining the orbit rather than the possibly-multiple discoverers and re-discoverers at each apparition.
Crommelin, together with Philip Herbert Cowell, a specialist in the mathematics of motion, simplified the method of calculating the perturbations (distortions) in the orbits of long-period comets. In their essay on the return of Halley's Comet, Crommelin and Cowell traced historical references to the comet's return as far back as 240 BC, and with some probability to 625 BC. They predicted the comet's return in 1910 to an accuracy of just over 3 days. For this work the authors were awarded the Lindemann Prize of the Astronomische Gesellschaft of the University of Jena, and both received an honorary doctor of science degree from Oxford University.
Crommelin took part in expeditions to observe total solar eclipses in 1896, 1900, 1905, 1912, and 1927. In 1919 he participated in the solar eclipse expedition to Brazil which aimed to determine the amount of the deflection of light caused by the gravitational field of the Sun. The results from these observations were crucial in providing confirmation of the General Theory of Relativity, which Albert Einstein had proposed in 1916.
Between 1898 and 1906 Crommelin prepared astronomical almanacs for observations of Mars, Jupiter, Saturn, and the Moon. He also contributed observations of comets and minor planets to the Journal of the British Astronomical Association for over 40 years, and was the author of Comet Catalogue (1925) and co-author with Mary Proctor of Comets (1937).
Dr. Andrew Claude De La Cherois Crommelin (1865-1939)
Born 6 February 1865 Cushendun
Married 14 October 1897 Laetitia Noble
Born in 1865 at Cushendun, Ireland, he was three when he moved with his parents to England. He was educated at Marlborough, whence he secured a scholarship to Trinity College, Cambridge, where he was, for what it is worth, 27th Wrangler, and took his BA degree. Subsequently he obtained an Oxford DSc. After two years as a schoolmaster at Lancing, he was appointed an Assistant at the Royal Observatory, Greenwich, a post he held from 1891 until 1927.
In 1888, when he was twenty-three, he had been elected a Fellow of the Royal Astronomical Society; he served for several years as Secretary, and from 1904 to 1906 as President, of the British Astronomical Association. He "took part in the Eclipse Expeditions of that Association of 1896, 1900, and 1905; also in the Expedition to Brazil of 1919".
This last journey was described, on 22 November 1919, in the newspaper "The Spere" as follows : "Astronomery: Two eclipse expeditions were sent out last May, one to Principle, on the east coast of Africa, the observers being Prof. Eddington and Mr. Cottingham, and the other to Sobral, in North Brazil, the observers being Dr. Crommelin and Mr. Davidson. Their object was to observe the eclipse with the special purpose of testing a new theory of gravitation put forward by Herr Einstein, a German mathematician."
Crommelin was a Christian gentleman, modest and unassuming, careless of appearance but always courteous. A Protestant in his youth, after taking his tripos he stayed on at college reading for Holy Orders in the Anglican Church, but about this time became unsettled in his religious convictions, ultimately entering the Roman Catholic Church in 1891.
He lived near his parents at Blackheath, handy also for the Observatory, and went out of his way to describe himself in 'Who's Who' as a Roman Catholic. He had four children, of whom one entered the priesthood while two were killed in a climbing accident on Pillar Rock, Ennerdale, in 1933.
With P. H. Cowell, he was the author of "Investigation of the Motion of Halley's Comet, from 1759 to 1910". According to the "Science News-letter" of 30 October 1926: "Giacobini's Comet, which returns to the vicinity of the earth every six and two-thirds year--- has come back again, according to Dr. Harlow Shapley, director of the Harvard College Observatory, and the place where it was found was very close to the position predicted a year ago by Dr. A. C. C. Crommelin of the Royal Observatory, Greenwich, England. The difference between the predicted and the observed place of the comet was about the diameter of the full moon."
In 1929 Crommelin demonstrated that comet Forbes 1928 III was identical with comet Coggia-Winnecke 1873 VII and comet Pons 1818 II, 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. In 1956 the comet returned to perihelion just four days later than Crommelin had predicted.
He died, aged seventy-four, in 1939. He had a crater on the moon named after him.
Source: (C.E.B.Brett, 1997.)
THE COMET’S TALE
Newsletter of the Comet Section of the British Astronomical Association
Volume 8, No 1 (Issue 15), 2001 April - pp. 9-11
‘The Comet Man’ A. C. D. Crommelin, B. A., D. Sc., F. R. A. S.
by John Fletcher
Mount Tuffley Observatory
This biography of A. C. D. Crommelin, written in 1992 April, all came about after I received a call from a most interesting lady aged 84 years who lives in Gloucester and only about a five minute drive from my home and private observatory in Gloucester, England. The lady's name is Sara Crommelin who married Peter the son of A. C. D. Crommelin, the comet man. Sara tells me she and Peter are the sole relatives of this famous astronomer who was famed for his computations of cometary orbits. Sadly his son Peter is in a nursing home at the moment and also Sara's own eyesight is not too grand she tells me. Sara also told me things about his private life including that of the great man’s sadness when he lost his eldest son and a daughter in a climbing accident.
Andrew Claude de la Cherios Crommelin was born in Cushendun, N. Ireland on 1865 February 6th and died in London on 1939 September 20th, some 9 months after he had been knocked down by a motor cyclist almost outside his home when on his way to church. He was the third son of the late Nicholas de la Cherois Crommelin, a descendant of Louis Crommelin, a Huguenot who was the founder of the linen trade in Ulster. He was educated at Marlborough College and then went on to Trinity College Cambridge, and graduated in 1886. In 1897 he married Letitia the daughter of Rev. Robert Noble, and had two sons and two daughters.
After graduation he went to Lancing College on the teaching staff. Then he tried his hand at electricity but soon gave that up. He had always been throughout his childhood keen on watching the sky and observing the stars and at Cambridge was a keen observer of the stars and built up a reputation for his knowledge of astronomy. He was elected into the Royal Astronomical Society before leaving the University in 1888. It was fortunate that in 1891 the appointment of an assistant at the Royal Observatory in Greenwich, was authorised by the Admiralty. Andrew sitting in competition with the late E. W. Brown secured the appointment.
He joined the staff of the Royal Observatory on 1891 May 11th. He took his place among the members of the regular staff making routine observations with the transit circle and the Sheepshanks equatorial. He was also put in charge of the altazimuth instrument designed by Airy for observing the Moon. Observing the occultations of stars by the Moon, and comets was put in his care. Crommelin's work was extensive at Greenwich and he was an expert in all his research as both observer and a computer. In 1911 he made an accurate determination of the Lunar parallax and prepared the ephemerides of both the Moon and outer planets including the path of Jupiter’s eighth satellite.
Crommelin went on many eclipse expeditions organized by the B.A.A. From Brazil Crommelin observed the 1919 Solar eclipse using a 4 inch refractor of 19 feet focus and secured some fine photographs, which determined there was a deflection of light in the gravitational field of the Sun beyond any question of doubt. He also determined the orbits of many comets and minor planets. This was recorded in an early number of the Journal of the British Astronomical Association. Indeed for many years he was the director of the comet section of the British Astronomical Association and President between 1904 and 1906 and in the year 1937 he received the Goodacre Medal. He was also a fellow of the Royal Astronomical Society for over fifty years and served on their Council from 1906 to 1932. He was also was Secretary from 1917 to 1922 and became their President during the years 1929 and 1931. He wrote their annual reports on minor planets and from 1916 the reports on comets as well. Crommelin was also the President of the International Astronomical Union’s sub commission on periodic comets from the year 1935 until his death. The Memoirs of the British Astronomical Association, Vol XXVI, Part 2, Comet Catalogue (1925), prepared by A. C. D. Crommelin.
At a meeting of the Astronomical Union in Rome (May 1922) Crommelin expressed his desire to produce a sequel to Galle's Cometenbahnen to bring up to date and enter improved orbits of comets for the period of time prior to 1893. The work was carried out with the help of the computing section of the comet section of the British astronomical Society. The comet catalogue was later published in 1925. Throughout this work he had been under great pressure at work and with very little cooperation from colleagues. He did however acknowledged the help he received by Miss Mary Proctor, who copied the orbits given in Astronomische Nachrichten and the bulletin Astronomique. Crommelin included the results of Dr Cowell and himself of the ancient returns of Halley's Comet. He also included many predicted elements of periodic comets even in the case when the comet was not observed. For their work Crommelin and Cowell were awarded the Lindemann Prize of the Astronomische Gesellschaft and also both received a D. Sc degree at Oxford University.
According to the records from the British Astronomical Memoir, Crommelin and Cowell computed the details for the following apparitions of comet Halley: BC240 from China, AD141 from China, AD530, AD607 from China, AD684 from China, AD837 from China, AD1066 from China and Europe, AD1145 from China and Japan, AD1301 from China and Europe, AD1835 and AD1909 (first photo August 24th). Crommelin also computed orbits for comets: Grigg - AD1902 (J.Grigg & Crommelin), Lowe - AD1913 (M.Viljev & Crommelin), Encke - AD1924 (L.Matkiewicz & Crommelin) and Wolf - AD1925 (Crommelin & A.Kahrstedt).
Crommelin was famed for computing that comet Forbes 1928 (III), comet Coggia- Winnecke 1873 (VII) and comet Pons 1818 (1) were all the same object and he predicted that the same object would return in 27.4 years, which it did. In 1948 the International Astronomical Union changed the name of the comet from Pons-Coggia-Winnecke- Forbes to Crommelin. The history of these many separate discoveries goes like this. Crommelin’s comet, not so named then, had been first observed by one of the greatest comet observers of all times, namely Jean-Louis Pons. Prior to sighting comet (1818 I) on 1818 February 23rd Pons had discovered no less than 16 out of the 17 comets observed during the beginning of the nineteenth century. The 1818 comet was skilfully discovered by Pons from his observing site (Marseille, France) at +40ºN when the comet was at -15º and only 54º to the Sun. It was slightly fainter than 7th magnitude. Pons was able to measure four positions of the comet but he could not determine an orbit. The comet was rediscovered later by Coggia also in Marseille and one day later by Winnecke in Strasbourg but very poor conditions allowed for only six days viewing. The comet of Pons and Coggia-Winnecke was not known to be the same comet at that time.
The orbital period of the comet had indeed remained unknown until Crommelin tackled the problem in 1928. In a long series of papers Crommelin had shown that Pons (1818 I), Coggia- Winnecke (1873 VII) and Forbes (1928 II) were three apparitions of the same comet. The 1845 and 1901 returns were sadly missed due to poor sky conditions. When it reappeared according to Crommelin's prediction in 1956 it was renamed after him. On this apparition it returned to perihelion only four days later than his prediction. Also in 1956, for the first time on record the comet displayed a short tail and it was favourably positioned for observation. It returned on schedule again in 1984 and this time again it was singled out for unusual attention. The International Halley Watch, while preparing to observe the most famous periodic comet of all (Halley) chose Comet Crommelin for a trial in preparation for the coming apparition of Halley's comet. The first visual sightings were from France on 1983 December 29th and of 12th magnitude. Only a few days later on 1984 January 3.8 it was of magnitude 10.5. It was observed in great detail especially in March 1984, even though the weather was poor for observing and the comet was not a dramatically bright object.
Nevertheless the comet has been very useful to science and indirectly contributed to the great success of the observations of Halleys comet. All this has greatly increased our understanding of comets in general (including of course Comet Crommelin). One of his most famous writings was "Essay On The Return Of Halleys Comet" in Publikation der Astronomischen Gesellschaft, No. 23 (1910), written with P.H.Cowell; and also the Comet Catalogue, Memoirs of the British Astronomical Association, 26, pt. 2 (1925), continued ibid., 30,pt.1 (1932).
Great astronomers like Crommelin must never be forgotten. It is their computing work (as it was called then) that has paved the way to our modern knowledge of astronomy. Crommelin’s sequel to Galle's Cometenbahnen certainly advanced cometry science in his day.
I wish to thank Sara and Peter De La Cherois Crommelin, his daughter in law and son for the information I have received to make this account of the great astronomer A. C. D. Crommelin possible. I would also like to thank H. Ridley (Comet Section, British Astronomical Association) and P. G. Hingley (Librarian, Royal Astronomical Society). Also thanks to Patrick Moore for his encouragement, given to myself, to delve into the history of this great astronomer's life and work.
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