The Caldwell Objects

nebula is a near impossibility, even when viewed
at an altitude of 4,200 feet under transparent
Hawaiian skies. At 23x the Cave looks like an illdefined
haze playing with an arc of roughly 7thmagnitude
suns. The weakly glowing gas is
peppered with many faint stars, making it almost
indistinguishable from the patchwork Milky Way
star fields permeating the region. I find that the
best eyepiece combination for glimpsing it is a 22mm
Panoptic and a 1.8x Barlow lens, which
together yield 41x through the Genesis.
Of course, finding the right magnification to
bring out the nebula turns out to be a delicate
balance between power and contrast. While the
nebula is best seen at 41x it virtually vanishes at
72x, though a filamentary "spike," which is a part
of the Cave, does dimly stand out against the
darkness. (This is the aforementioned ionization
front.) Sweeping the telescope back and forth
over the area will help the eye pick out the
nebula's brightest (though low-contrast) glow. I
find it at the center of the nebula, just west of the
darkest part of the cavity, near a triangle of 9thmagnitude
The Caldwell Objects
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suns. It is this 10'-wide area that I estimated to
shine at an apparent magnitude of 10.0. A patch
of dark nebulosity can be seen east of the triangle.
Also, brief looks into the eyepiece will help more
than a prolonged stare. But beware! It's easy for
one's imagination to creep into the mind's eye.
There are many faint glows in the field, some of
which I'm suspicious of— even though I included
them in my drawing — because they tend to
follow streams or clumps of faint stars rather
closely. lust as some double stars (like M40)
appear fuzzy at low power, so too do lines of
stars and patches of the Milky Way. The use of a
UHC filter should boost the contrast and bring
out the nebula, which covers an area roughly 50
light-years across. If you only suspect seeing the
Cave Nebula, do not give up on it. Atmospheric
clarity varies, so try on many nights. Once
spotted, the nebula actually becomes easier to see
on subsequent nights.
Unfortunately, I was not able to see the
entire dark mouth of the Cave in the 4-inch. Your
challenge, then, is to determine the smallest
aperture required to see this elusive feature
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