What´s the difference between the historically-corrected and the revised NGC catalogs?
The original NGC was created in 1888 when very little was known about the universe and astronomy equipment had much less precision than today. Many astronomers have since corrected some of the data in the NGC with newer technology and knowledge, and two of these catalogs have become very popular. Some major differences are that the revised version separates some objects originally unknown to be made of smaller individual objects, by adding letters to the NGC number. The HCNGC does not introduce new object entries, but extends the NGC with details of when, who, and with what equipment the objects were found. Both list more precise positions and in the J2000 equinox.
