The Caldwell Objects

and contains some 1,890 members, while NGC
3766 is a mere 24 million years young with 137
known members (though the larger number of
M37 stars may simply be due to that cluster
having been studied more often).
NGC 3766 is another one of Abbe Nicolas
Louis de Lacaille's finds and is listed in his 1755
catalog as the seventh of his Class III objects
(stars accompanied by nebulosity). Through his
½-inch 8x telescope Lacaille saw "three faint
neighbored stars surrounded by nebulosity." But,
as with many of Lacaille's finds, the nebulosity
does not exist; it is merely unresolved starlight.
Although NGC 3766 is visible to the naked eye
under a dark sky, it is not obvious. It lies in a
patchy, star-rich section of the Milky Way, and its
5th-magnitude glow requires one to know
precisely where to look for it. Particularly
deceptive is a 30'-long rectangular asterism
oriented north-south; its southern base lies about
15' from NGC 3766's northern fringe. This
clusterlike grouping looks larger and fuzzier to
the naked eye than does NGC 3766, and it could
be mistaken for
97
our tiny target. It's best first to identify NGC 3766
in binoculars, then to look with the naked eye. In
7x35 binoculars its half-dozen brightest suns
form a sideways Τ that stands out at the
northwestern end of a roughly l⅓°-long chain of
four similarly bright, equally spaced stars. This
chain starts about 1° northeast of Lambda
Centauri and continues northwestward toward
NGC 3766.
At 23x in the 4-inch Genesis the cluster's
brightest stars are colorful 8th- to l0th-magnitude
jewels strewn across a carpet of dim, white
suns. James Dunlop first noted the star's colors in
the 1820s, writing: "The greater number of the
stars are of a pale white colour. There is a red star
near the preceding [western] side; another of the
same size and colour near the following [eastern]
side; another small red star near the centre; and a
yellow star near the south following
[southeastern] extremity, all in the cluster." And
modern observers still comment on them: in
Volume 7 of the Webb Society Deep-Sky Observer's
Handbook, NGC 3766 is described as having some
"orange and yellow
The Caldwell Objects 389