Every so often I descend from my austere ivory tower and engage in discussion on various astronomy discussion boards. In this recent exchange, I suspect that the person who posted the original question is not really part of the target group for this site, but the exchange has been entertaining and has attracted about 40 new visitors to Galaxy Map so far. If you are one of them, welcome!
As promised in my last blog entry, I've created overlay maps for the Gum, RCW and Sharpless nebulae. You can find the links and a preliminary analysis, including a description of a surprising error in the Sharpless catalog, here.
As I've been going through my commentary on the RCW catalog, I've come to realise that there are several dubious or erroneous cross identifications in the RCW catalog, especially with regard to objects in the Gum catalog. In several cases, it appears that Colin Gum was actually referring to a different object or only part of the object as later defined by RCW. To deal with this, I'm going to put up a map showing the locations and extents of all the objects in the Sharpless, RCW and Gum catalogs.
My commentary on the Gum catalog currently uses the coordinates for these objects given in SIMBAD. However, these coordinates are often derived by SIMBAD using identifications with other nebulae and do not reflect the actual data given in Gum's original catalog. Unlike the Sharpless and RCW catalogs, Gum's original catalog data is not available through Vizier, so as a first step, I have manually entered Gum's original data for each of the 97 entries in his catalog into an Excel-format spreadsheet.
Gum supplied 1900 epoch RA and Declination data for these objects. I've used the Python ephem library to convert these into current l and b galactic coordinates and added these to the spreadsheet as well. (Note that the galactic coordinates supplied by Gum in his original catalog are based on the old Lund pole system and I have not included these in the spreadsheet.)
You can find the Gum spreadsheet here. I'll post another blog entry when the nebula map is ready.