Reference Work Entry

Biographical Encyclopedia of Astronomers

pp 552-553

Date:

Delporte, Eugène-Joseph

Born Genappe, Brabant, Belgium, 17 January 1882

Died Uccle near Brussels, Belgium, 19 October 1955

The Belgian astronomer Eugène Delporte is credited with the discovery of at least 66 asteroids in modern catalogs, and was the final authority in establishing the boundaries of constellations officially adopted by the International Astronomical Union [IAU]. Delporte studied mathematics at the Free University of Brussels, and received a doctorate in mathematical and physical sciences in 1903. He was employed the same year at the Royal Belgian Observatory at Uccle, and appointed director of the Uccle Observatory in 1936. Even after his retirement in 1947, Delporte continued observational work at Uccle. He died from a heart attack while examining a photographic plate.

Initially put in charge of time and meridian measurements, Delporte eventually specialized in the search for minor planets through systematic photography of the sky. In doing so, Delporte established a tradition continued to this day by his successors at Uccle. His first success was (1052) Belgica, the first minor planet discovered from Belgium. As of 2004, 66 minor planets discovered by Delporte had been numbered and named; two of these can make close approaches to the Earth: (1,221) Armor, discovered in 1932, and (2,101) Adonis, discovered in 1936 but later lost and then found again in 1977. Adonis’ orbit crosses the Earth’s orbit and reaches its perihelion inside the orbit of Venus.

Delporte made an independent discovery of a comet, 57P/1941 O1, on 19 August 1941. Because of the war – Belgium was then occupied by the German army – he was unaware of earlier observations by Daniel du Toit (18 July) at Bloemfontein, South Africa, and G. Neujmin (25 July) in the Crimea (then part of the Soviet Union). Delporte could only communicate his discovery to institutes abroad after receiving special military permission, which he finally obtained with the help of a German officer who had been a geographer before the war. The comet is now known as 57P/du Toit-Neujmin-Delporte.

Delporte is perhaps best known for his work in establishing the official boundaries of the constellations. In 1922, the IAU fixed the number of constellations at 88. At that time, Delporte and his fellow countryman L. Casteels proposed to lay down arcs of circles as boundaries for the northern constellations. The American Benjamin Gould had already introduced such delineations for the southern constellations in 1877. In 1925, the IAU created a subcommittee to settle the matter with Delporte and Casteels among its members. On Delporte’s proposal, the subcommittee decided to use only parts of parallels and meridians based on the 1,975.0 equinox as boundaries. In fixing the boundaries, the traditional shapes of the constellations were respected as much as possible and reattribution of stars from one constellation to another was reduced to a minimum. The final demarcation was made by Delporte alone in order to obtain a maximum of uniformity in the results.

When Delporte finished this work in 1927, the IAU asked him to also delimit the southern constellations using the same principles. Gould had previously used oblique arcs of circles in his delineation. Delporte replaced these by combinations of parallel and meridian arcs, without changing one star’s constellation in Gould’s catalog. The whole system of boundaries was published by the IAU in 1936 under the title Délimination scientifique des constellationsand has been in use unchanged since then.

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