John Louis Emil Dreyer

Born: Copenhagen, 13 February 1852
Died: Oxford, 14 September 1926

Family: father - John Christopher
married - Katherine Tuthill of Kilmore, Co Limerick, 1875
children - three sons and one daughter

Address: Armagh Observatory, 1882-1916

Distinctions: Gold Medal, Copenhagen (1874), Gold Medal - Royal Astronomical Society (1916), President R.A.S. (1923-1925), D.Sc. Belfast, Hon. M.A. Oxford

Biography: From his schooldays in Copenhagen, J.L.E. Dreyer showed unusual ability in history, mathematics and physics - the subjects which were to form the background to his later work.

In 1874 he accepted the position of Assistant to Lord Rosse at Birr where the giant six-foot Leviathan, at that time the largest telescope in the world, was at his disposal. Here he initiated a comprehensive survey of star clusters, nebulae and galaxies. From 1878-1882 he became assistant at Dunsink Observatory before moving to Armagh where he became Director in 1882.

Financially, Armagh Observatory was destitute, with no prospect of replacing its aging instruments. Though Dreyer obtained a new 10-inch refractor by Grubb, the lack of funding for an assistant, precluded him from a continuation of traditional positional astronomy. Instead he concentrated on the compilation of observations made earlier, namely The Second Armagh Catalogue of Stars and what became his most important contribution to astronomy, The New General Catalogue of Nebulae and Clusters of Stars (NGC). In this catalogue, which to this day remains the standard reference used by astronomers the world over, he listed 7840 objects. This he followed with two supplementary Index Catalogues (1895, 1908) which contained a further 5386 objects. It is the order in which they appear in these catalogues that defines the name of many prominent galaxies, nebulae and star clusters.

Throughout his life, Dreyer had a fascination for the early development of his subject and in particular, the work of his fellow countryman, Tycho Brahe, on whose work Kepler based his theories of planetary motion. Dreyer's account of the life and work of Tycho, published in 1890 is the standard biography in English. Subsequently, he commenced his magnum opus, a comprehensive version in Latin of the complete works of Tycho, eventually to fill 15 volumes. In 1906 he published The History of the Planetary System from Thales to Kepler, another classic of historical astronomy.

Photograph of Dreyer as a young man

Dreyer (seated at doorway) with his son at Armagh Observatory

Dreyer (standing) with his son at Armagh Observatory

Publications from the ADS

Dreyer's History of the Armagh Observatory

The Creation of the NGC

Dreyer and the NGC By Eric Lindsay

Admiral Sir Frederic Charles Dreyer (son)

Further reading:
J.A. Bennett: Church, State and Astronomy in Ireland, Armagh Observatory, 1990.

Author details: cjb

arm.ac.uk, John Butler, Armagh Observatory, N. Ireland

Last Revised: 2009 November 5th