The Lake County Astronomical Society

Astronomy Bio...John Louis Emil Dreyer

Jay Bitterman

John Louis Emil Dreyer was born in Copenhagen on February 13, 1852. His father was John Christopher Dreyer. While growing up in Copenhagen he became interested in history, math and physics.

At the age of 14 his interest in astronomy was stimulated after reading a book about Tycho Brahe. His curiosity in astronomy was encouraged by Schjellerup an astronomer at the Copenhagen University. In 1869 Dreyer started his studies at the university. In 1870 he was given free access to the all of the instruments in the University Observatory and observed his first comet. In 1872 Dreyer published his first astronomical publication describing the comet's orbit.

In 1874 he was appointed assistant at Lord Rosse's Observatory at Birr Castle in Parsonstown, Ireland where he worked with the world's largest telescope (having a six-foot aperture) nicknamed the Leviathan.

While in Ireland he focused on observing and surveying galaxies, nebula and star clusters, a topic that occupied the majority of his time for the next 14 years. In 1876 he published an important paper, that he was quite aware of, that dealt with the inherent error involved with astronomical observations of objects such as nebula. In 1877, at a meeting of the Royal Astronomical Society, he presented data on more than a thousand new nebulae and corrections to John Herschel's General Catalogue of

nebulae and star clusters. In 1878 acquired a similar post at Dunsink Observatory at the University of Dublin, and in 1882 he became Director of the Armagh Observatory, where he remained until he retired in 1916. In 1886 Dreyer augmented this work at Armagh that led to his publishing the Second Armagh Catalogue that included information for over 3,000 stars.

The Royal Astronomical Society then asked him to organize a new comprehensive catalogue of nebulae and star clusters and incorporate all the modern data that would supersede Herschel's old General Catalogue (GC). He completed this enormous task in just two years but because of the rapid accumulation of additional information it was necessary to publish two supplementary indexes. The New General Catalogue of Nebulae and Clusters of Stars (NGC) in 1895 and its supplements form the Index Catalogues (IC) in 1908. All in all these three catalogues contained 13,226 entries and have remained standard references for deep-sky objects that gained international recognition as the standard reference material. The NGC also contains 17 objects that that Dreyer himself discovered.

With the completing of the catalog, Dreyer decided to write the biography of his hero, Tycho Brahe. In 1890 the biography was published and the 15 volume series that detailed all of Brahe's work that he started in 1913 was completed in 1919. Additional writings included, at the time, the only authoritative and complete history of astronomy and an edition of the complete works of William Herschel.

When he retired in 1916 Dreyer was awarded the highest honor of the Gold Medal from the Royal Astronomical Society. He had been a Fellow of the Royal Astronomical Society since 1875. In 1970 he was honored by having a Moon Crater named after him.

He was married Katherine Tuthill of Kilmore, Co Limerick, in 1875 and they had children three sons and one daughter. Dreyer died in Oxford on September 14, 1926.