The Lesser Known Deep Sky Objects Catalogues
We all know that many of the objects we chase around the night sky are listed as part of a catalog other than the New General Catalog (NGC) or the Index Catalog (IC). However, two of the lesser known catalogs that I’ve come across are the Sharpless and RCW catalogs. As with the Caldwell and Barnard catalogs, I was curious about these catalogs, what they were, how they came about and the people they were named after. So, I decided to investigate and learn a little more about them.
Astronomer Stewart Sharpless joined the staff of the U.S. Naval Observatory in Flagstaff sometime in 1953. Just to note, Flagstaff Arizona is also home to the Lowell Observatory; they are separate facilities.
He surveyed and cataloged Hydrogen II (HII) regions of our galaxy using data from the Palomar Sky survey. 2 editions of his work were published, the first later in 1953 and the second edition in 1959 which contained just over 300 objects.
Many of the items in the Sharpless catalog are also listed in other catalogs, such as the New General Catalog (NGC), Messier object catalog, the Caldwell catalog and the RCW catalog.
Examples of Sharpless catalog objects that are also contained in other catalogs are:
- M16, the Eagle Nebula is Sharpless 2-49;
- M8, the Lagoon Nebula is Sharpless 2-25;
- M20, the Trifid Nebula is Sharpless 2-30;
- NGC 7635, and the Bubble Nebula is Sharpless 2-162.
There is one object that I’ve imaged and processed that is only in the Sharpless catalog; the Tulip Nebula, designated only as Sh2-101. All of these objects are consistent targets for astro imagers.
I became aware of the RCW catalog through my time on Telescope Live; I was unaware of it before then. This is a catalog of Hydrogen Alpha regions seen only in the Southern Hemisphere of the Milky Way.
It was put together by 3 people; Alexander William Rodgers, Colin T. Campbell and John Bartlett Whiteoak who all worked at the Mount Stromlo Observatory in Australia during the 1960s.
This catalog contains 182 objects, many of which overlap with the Gum, NGC, Caldwell and Sharpless catalogs. Two well known RCW objects are the Statue of Liberty Nebula, RCW 57 which is also known as The Torchbearer and the Butterfly Nebula, RCW 124.
I’ve not been able to find much public documentation such as books on either of these 2 catalogs for my library, so if anyone knows of any resources like these please let me know.
As always, stay safe, get more people to turn their lights off at night and clear skies!
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