The Caldwell Objects

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NGC 6744
Type: Barred Spiral Galaxy
(SABbc)
Con: Pavo
RA: 19 h 09.7 m
Dec: -63° 51'
Mag: 8.6
Dim: 20.8' x 13.3'
SB: 13.9
Dist: 34 million light-years
Disc: James Dunlop, included
in his 1827 catalog
J. HERSCHEL: Pretty bright, round, [at]
first very gradually, then suddenly very
much brighter in the middle; total
diam[eter] 2', but that of the bright part
15 arcseconds. (h 3776)
GC/NGC: Considerably
bright, considerably large, round, very
gradually, suddenly very much brighter in the
middle, resolvable.
tion (-56° 44') makes it visible, in principle, from
latitude 33° 16' Ν (ever so slightly farther north if
you consider refraction) and points south. This
means it is visible from most of the southern
United States.
Globular star cluster NGC 6752 (Caldwell
93), however, is more challenging than Peacock.
It lies 10° west-southwest of Peacock, so you
basically need to be at, or south of, latitude 30° Ν
to see it. That means the cluster just misses being
visible from the grounds of the Texas Star Party
near the McDonald Observatory. But if some
enterprising TSP attendee were to go and view
the lights of Marfa, Texas, or drive south of the
30th parallel on their way, say, to Presidio at the
Mexican border — and take a
93 & 101
pair of 7x50 binoculars with them — they just
might spot the southernmost Caldwell globular
visible from the continental United States.
NGC 6752 is the third-easiest globular star
cluster to resolve, by virtue of its horizontalbranch
magnitude of 13.7, which compares
favorably to NGC 6397's (12.9) and M4's (13.4). (A
cluster's horizontal-branch magnitude indicates
how bright a fair fraction of its stars are;
according to deep-sky expert Brian Skiff, a
telescope must show stars of that brightness to be
able to resolve the cluster well.) Robert Burnham
Jr. ranked NGC 6752 among the finest dozen
globulars in the heavens. At magnitude 5.4 it can
be seen with the naked eye, and it ranks 5th
among globulars in total brightness.
The Caldwell Objects 371