The Caldwell Objects

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NGC 7006
Type: Globular Cluster
Con: Delphinus
RA:21 h 01 m 29.5 s
Dec:+16°11’15"
Mag: 10.6
Diam: 3.6'
Dist: 135,000 light-years
Disc: William Herschel, 1784
W. H ERSCHEL: [21 August
1784]: Very bright, small,
round, gradually much
brighter in the middle.
Resolvable. (Η I1-52)
GLOBULAR CLUSTERS, SCINTILLATING BOUQUETS of
hundreds of thousands of suns, adorn the most
distant reaches of our Milky Way. While bright
stars and open clusters populate our galaxy's
flattened disk, most globular clusters lurk in the
galaxy's spherical halo, a cold and bleak domain
of old suns and mystery matter that spans a
quarter million light-years of space. But NGC
7006 (Caldwell 42) in Delphinus is exceptional
even among globulars. It lies on the halo's very
fringe, 135,000 light-years from Earth, and may
be a part of the galaxy's outer halo, or corona.
From our station on Earth, NGC 7006 lies nearly
twice as far as M54, the most distant Messier
globular, though it is twice as close as the most
distant Caldwell globular: NGC 2419 (Caldwell
25), the famous Intergalactic Wanderer in Lynx.
NGC 7006 lies 127,000 light-years from the center
of our galaxy. Of the 150 or so globular clusters
known within our Milky Way, NGC 7006 is one
of the most remote; as of 1997 it was considered
the eighth most far-flung globular from both the
The Caldwell Objects
GC/NGC: Bright, pretty large, round, gradually brighter in the
middle.
42
Earth and the galactic center.
If we consider the sheer immensity of the
galactic halo and the paltry number of globulars
that populate it, we can begin to understand the
true loneliness of space. The distribution of the
globulars, however, is not uniform. About onethird
of our galaxy's globulars are concentrated
toward the galactic center in the direction of
Sagittarius, while the others are scattered far
above and below the galactic plane. The famous
Harvard College Observatory astronomer
Harlow Shapley first suspected that the distribution
of globulars was intimately related to the
structure of the Milky Way galaxy, and in the
1910s and '20s he used the great 60- and 100-inch
reflectors atop Mount Wilson in California to
survey them. His most important contribution
was his systematic study of variable stars within
the clusters. Earlier work by Solon Bailey (also at
Harvard) had shown that the majority of the
variable stars in globular clusters brightened and
dimmed over periods of hours. Now known as
RR Lyrae stars, these
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