The Caldwell Objects

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thwart your efforts. Be sure to take frequent deep
breaths and a series of quick looks rather than
one prolonged gaze, which will just drain your
"eye batteries." I found NGC 3201 a bit more
difficult to see with the naked eye than the
similarly bright and large globular cluster M2 in
Aquarius. If you fail, try again on another night.
In 7x35 binoculars the cluster is a cinch, and
at 23x in the 4-inch it is a fabulous globular with
an intense core surrounded by a wobbly
envelope of stars. The apparent direction and
extent of the envelope depend on how you hold
your head or use your averted vision; this is
probably what Herschel meant when he called
the cluster "irregularly round." With averted
vision the halo is definitely mottled, and some of
its outliers can be resolved at low power. The
brightest members of the cluster shine at
magnitude 11.7, and its horizontal-branch
magnitude of 14.8 should enable anyone with an
8-inch Schmidt-Cassegrain to look deep into the
cluster's maze of suns. Even in the 4-inch at low
power I can make out hints of
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"spiral" structure and an arc of detached suns to
the west-northwest. Before moving on to higher
magnification, sweep the cluster's general area at
23x and see if you don't encounter a copse of
double stars, many of which are so tight they
appear fuzzy. Many sources complain that the
cluster's cataloged size is not realistic, but I
disagree; when viewed under dark skies with
low power the cluster's full 20' span can be
visualized. In physical terms this translates into
nearly 100 light-years.
At 72x much of the cluster is immediately
resolved. Most fantastic is a bright V of stars. Its
apex starts at the north-northeastern side of the
cluster's main "starcloud," which suddenly
branches into two arms that extend south and
southwest. The stars in the branching arms appear
remarkably obvious, and most are of similar
brightness. This is one of the cleanest visual
structures I've ever seen in a globular. A pompadour
of dim suns curls off the main cloud to
the northwest, and a tail of starlight sweeps in
the same direction from the southern side to the
outer halo before ending in a prominent
Deep-Sky Companions: The Caldwell Objects