The Caldwell Objects

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cluster and ½° southwest of the 7th-magnitude
double star Struve 953, which itself is roughly 1°
south of 15 Monocerotis. (By the way, did you
happen to notice that Herschel discovered NGC
2261 the night after Christmas?) Next to the
symphony of dust and gas described above,
Hubble's Variable Nebula looks like a single note
of nebulosity, a puff of breath, an ignited match
next to a raging forest fire. Or so it seems in deep,
wide-field photographs. Visually, however, NGC
2261 is the most prominent glow among all this
nebulous wonder.
So condensed is the light of the nebula
around R Monocerotis that I have seen it in 7x35
binoculars, though with effort under a very dark
sky. The difficulty is not so much in seeing a l0thmagnitude
"star" with 7x35 binoculars from a
dark site but in separating it from a neighboring
11th-magnitude star only about 2' to the
northeast. At 23x in the 4-inch I almost mistook
the pair for a double star in one of my sweeps.
Once you've located this "double" with your
telescope, use averted vision and wait a moment;
the nebula fanning off of R Monocerotis should
swell prominently into view. Again, both the fanshaped
nebula and "star" at its apex are variable.
Walter Scott Houston has noted that at times the
nebulosity associated with R Monocerotis has
been detected with a 3-inch telescope, while at
other times a 10-inch was required. When I
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was viewing it in April 1997, the nebula was
definitely fan-shaped at 72x. The fan was
directed to the north-northwest of an obvious
knot of nebulosity (namely R Monocerotis) at its
southern apex. The fan's edges were best defined.
I saw little detail inside the fan at this
magnification, so the object looked like a comet
with two sharp ion tails. At high power,
however, the view was more complex — and
most fascinating. The fan's eastern side was thin,
like the shaft of a feather, while the western edge
appeared less sharp. About halfway "up" the fan
a faint arc of material curved "over" R
Monocerotis like a single auroral flame. A dim
knot of material could be seen near the center of
this "flame"; from it an even fainter wisp of
nebulosity seemed to flare before fading to the
northwest. Do not fear using extremely high
powers on NGC 2261, for it takes magnification
well.
Those who own CCDs may want to follow in
Lampland's footsteps and consider undertaking a
long-term study of NGC 2261. Such a study
could yield some interesting and valuable results.
Various amateurs have already used their CCD
images to create "movies" that dramatically
illustrate shadows sweeping across the nebula.
By the way, in 1949 Hubble's Variable Nebula
became the first object to be officially
photographed by the famous 200-inch reflector
on Palomar Mountain.
Deep-Sky Companions: The Caldwell Objects