John Dreyer and the NGC

President's Paragraph: June 2016

Hubble Ultra Deep Field image

Looking once again at an image of the Hubble Ultra Deep Field image, wishing it were the kind of sky I could see here in Oregon, I started to think, also once again, about NGC numbers and IC numbers and wondering what exactly was behind this attempt to label each and every item in the sky.  Assuming you want to know too, I did some research. 

John Louis Emile Dreyer

John Louis Emile Dreyer

Most of what I learned comes from the obituaries of John Louis Emil Dreyer, the Danish/French astronomer who created the NGC system.  Inspired by Tycho Brahe, he dedicated himself to astronomy early in life, and began his career in 1874 as an assistant to Lord Rosse, son of the Lord Rosse who built the Leviathan Telescope that still stands at Birr Castle in Ireland, County Offaly.  While there he made many of his own observations, but also collected observations from other astronomers, and most notably, corrected errors in the work of previous observers, including John Herschell’s General Catalog of Nebulae and Clusters (1864).  In 1882, Dreyer became the Director of Armagh Observatory, County Armagh, Ireland, where he spent the next thirty-four years.  He immediately set out to collect, edit and correct previous observations made at the Observatory, which had already published its first catalog.  He published a second catalog for the Observatory, but was then asked by the Royal Astronomical Society to gather together several various lists and catalogs and to produce the definitive catalog.  The product of that work is the New General Catalogue of Nebulae and Clusters, being the catalogue of Sir John Herschel, revised, corrected, and enlarged, published in 1888.  NGC for short.  The catalogue contains 7840 objects, but Dr. Dreyer published two supplements to the NGC, called Index Catalogs, in 1895 and 1908 which added more than 5,000 more objects to the system.  Since the concept of galaxy was not in common use at the time, all items were referred to as nebulae if they weren’t obviously star clusters.  These three publications, nevertheless, are still the foundation for identifying and labeling everything we amateurs are likely to want to look for.  The books are collectively referred to as the NGC/IC.   

Since final publication, there have been several revisions and updates to the NGC/IC reference data.  You may stumble upon a Revised NGC or NGC 2.000 or a Complete New NGC, etc.  All of these have attempted to correct mistakes in the previous work and expand upon what has already been catalogued, though inevitably each of them has also introduced its own errors.  None of them is perfect, each has its quirks, so for the general purposes of amateur observing, the 1888 NGC and its IC supplements will continue to be our observing foundation a while. 

Dr. Dreyer eventually became president of the Royal Astronomical Society in England.  He had married an Irish woman and their four children all served in the British military.  In the last ten years of his life, after his retirement, Dr. Dreyer dedicated his years to compiling and editing the works of Newton and Brahe, producing a fifteen volume set of the complete works of Brahe.  In his elderly years, with his white beard and many honors and awards, Dr. Dreyer was well-known figure in Armagh, described by a neighbor as, “he just looked like an astronomer.”  I hope that June brings many many NGC galaxy-nebulae into your view.

June 1-4: Maupin Wapinitia Star Party (members and guests)
June 3: Downtowners
June 6: Board Meeting
June 8: Astroimaging SIG
June 10: Rooster Rock RCA Star Party (members and guests)*
June 11: Stub Stewart Star Party*
June 11: OMSI Public Star Party: Summer Solstice Celebration
June 20: New Member Orientation
June 20: General Meeting (Solar Eclipse Viewing)
June 22: Cosmology Astrophysics SIG
June 25: Telescope Workshop SIG
June 25: Haggart Observatory public observing and volunteer opportunity

* Please note that if you want to go to a smaller, quieter club-members-and-guests only star party, you can attend Rooster Rock on Friday night, the 10th.  Also, as usual, Stub Stewart will be open to stargazers.  And although we have a club party scheduled at Stub Stewart for Saturday night, if you go to either Stub Stewart or Rooster Rock on Saturday night, the 11th, you will be at an OMSI-sponsored public star party.  If you bring a scope, you will be able to clock your time on Saturday night as volunteer time.