The Caldwell Objects

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The Spindle
NGC 3115
Type: Lenticular Galaxy (SO)
Con: Sextans
RA: 10 h 05.2 m
Dec:-07° 43'
Mag: 8.9
Dim: 6.9' x 3.4'
SB: 12.1
Dist: 22 million light-years
Disc: William Herschel, 1787
W. H ERSCHEL: [Observed 23 February 1787] Extremely bright,
considerably large, much extended, 45° from south preceding
to north following [from southwest to northeast]. Has a bright
nucleus 2' long, faint [branch ?] 5' long. (Η 1-163)
GC/NGC: Very bright, large, very much extended
ONE OF THE MOST BEAUTIFUL GALAXIES IN the
heavens awaits small-telescope users in the
obscure southern constellation Sextans. NGC
3115, the famous Spindle, lies about 20° south of
Regulus, but few amateurs point their telescopes
at it. Sextans is a boxy southern constellation with
stars no brighter than magnitude 4.5, which isn't
a problem if you live under a dark sky. But if you
have to contend with city or suburban lights,
navigating that starless tract is like rowing a boat
blindfolded. This is unfortunate, since NGC 3115
is a splendid object. It is essentially no farther
south than the great Orion Nebula, and at upper
culmination it is fully one-third of the way up the
sky from horizon to zenith at midnorthern
latitudes.
At a glance it seems odd that NGC 3115
escaped Messier's careful gaze. After all, the
galaxy is close to the ecliptic, placing it within
the comet haystack scanned by most 18th-century
comet hunters. In fact, Messier discovered
The Caldwell Objects
toward position angle 46°, very gradually then suddenly much
brighter in the middle to an extended nucleus.
53
objects farther than NGC 3115 from the ecliptic.
The galaxy is certainly obvious enough in today's
instruments. In fact, NGC 3115 is a grander sight
than many galaxies in Messier's list. So how did
he "miss" it? Let's first consider what NGC 3115
would have looked like through Messier's lessthan-perfect
telescopes. Messier used about a
dozen different telescopes ranging from reflectors
with inefficient speculum mirrors (the largest
having an 8-inch aperture) to simple refractors
with apertures up to 3½° inches. Certainly, the
galaxy should have been easily discernible in a 6-
or 8-inch telescope. But ponder these words by
Adm. William Henry Smyth, who describes his
view of NGC 3115 through a 6-inch refractor: "It
is remarkable that this object was very clearly
distinguished in my telescope; for [Herschel] says
it was scarcely perceptible in his 20-foot when he
gave it only six inches of aperture." Of course, the
clear glass of Smyth's 6-inch refrac-
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