Originally Posted by ngc3314

The good news is that the NGC numbers are in running order of right ascension. The bad news is that the right ascension was as estimated (often rather poorly by today's standards) and was expressed in the then-current epoch of 1855 (not so new anymore). By now, precession has changed the RAs by amounts which depend on location in the sky, so that NGC objects with very different declination can be substantially out of RA order. This is the largest catalog I can think of with serially numbered entries which is that old, but the problem also occurs with the UGC (epoch 1950). The Third Reference Catalog would list the NGC numbers of galaxies on each page at the bottom, evidently for those of us who would try to find galaxies by paging through looking at the NGC numbers and hoping the declination wouldn't have not them too far out of order. For example, NGC 3310 is about 40 degrees to the north of 3308,9,11,12,13... and has thus jumped line in contemporary coordinates.