What is a Caldwell object?

One of 109 bright deep-sky objects Patrick Moore listed in 1995 because Messier had not. The two catalogues are deliberately disjoint, so a Caldwell number never names something that already has an M number.

By declination, from the far north to the far south. C 1 sits near the pole, C 109 close to it at the other end, and an observer's latitude decides how much of the run is reachable at all.

Can one observer see all of them?

Not from one place. The list spans both hemispheres by design, so completing it means travelling — which is the opposite of the Messier list, all of which clears the horizon from mid-northern latitudes.

Is it as well known as Messier's?

Less so, and it is also less uniform: it holds some of the finest objects in the sky next to a few that need a large telescope and a dark site. Messier's list was constrained by one instrument; this one was not.

What kinds of object are on it?

The same three families as Messier's — galaxies, nebulae and clusters — plus things his list has no example of, including a dark nebula, the Coalsack at C 99, and the two halves of the Veil catalogued separately as C 33 and C 34.

How many Caldwell objects are there?

109, numbered C 1 to C 109 in order of declination — C 1 is the northernmost and C 109 the southernmost. The count matches Messier's own 109 published objects deliberately.

Why is it called the Caldwell catalogue?

Patrick Moore's full surname was Caldwell-Moore. M was already the Messier catalogue's letter, so he used the other half of his name.

Do Messier and Caldwell overlap?

No. Moore's rule was that a Caldwell object is one Messier did not list, so the two catalogues together are 219 distinct objects.

The Caldwell catalogue

105 OF 109

Patrick Moore noticed that Messier's list, compiled from Paris, misses some of the best objects in the sky — the whole southern hemisphere among them — and in 1995 published 109 more to fill the gap. He numbered them by declination, from the far north to the far south, and used the C of Caldwell because Messier had already taken the M.

STAR CLUSTER · 42 GALAXY · 35 NEBULA · 28

NOT IN THIS CATALOGUE
4 entries are missing here — C 9, C 14, C 41, C 99. They are objects the upstream catalogues this site merges do not carry as a single row, usually because they are a naked-eye asterism or a pair of clusters catalogued separately.

The Caldwell catalogue

COMMON QUESTIONS