The Caldwell Objects

3 7
NGC 6885
Type: Open Cluster
Con:Vulpecula
RA: 20 h 11.6 m (derived from
Herschel's discovery
position)
Dec: +26° 28' (derived from
Herschel's discovery
position)
Mag: 8.1 (not including 20
Vulpeculae)
Diam: 20'
Dist: 1,950 l.y
Disc: William Herschel,
1784
W. HERSCHEL: [Observed 9
September 1784] A cluster
of coarsely scattered stars,
not rich. (H VIII-20)
GC/NGC: Cluster, very
bright, very large, rich in
stars, little compressed,
stars of magnitude 6 to 11.
CALDWELL 37, THE OPEN CLUSTER NGC 6885 in
Vulpecula, poses a problem. So, too, does open
cluster NGC 6882, also in Vulpecula. On modern
star charts, NGC 6882 is superimposed upon
NGC 6885 (or vice-versa). But this was not
always the case. That brings us to the main
problem: star charts and references are not
consistent in the way they plot or portray the two
clusters, so it's difficult to know which object we
are viewing when we point our telescopes
toward these clusters' part of the sky. There is a
history behind the confusion, and I will recount
some of it below. But first let's look at the issues
confronting amateurs who want
The Caldwell Objects
37
to locate and identify Caldwell 37.
Decades ago, observers using the reigning star
charts of their day would have had no problem
identifying NGC 6885. The 1962 edition of the
Skalnate Pleso Atlas of the Heavens shows NGC
6885 as a sizable object (20' wide) centered on the
6th-magnitude star 20 Vulpeculae. So, too, does
the 1966 edition of Norton's Star Atlas and the
first (1981) edition of Wil Tirion's Sky Atlas 2000.0.
The 1978 edition of Robert W Burnham . Jr.'s
Celestial Handbook lists NGC 6885 as an object 20'
across, with 35 stars of 6th to 11th magnitude, 20
Vulpeculae included. No one had to worry about
confusing NGC 6885
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