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The Caldwell Objects

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nebula is a near impossibility, even when viewed<br />

at an altitude of 4,200 feet under transparent<br />

Hawaiian skies. At 23x the Cave looks like an illdefined<br />

haze playing with an arc of roughly 7thmagnitude<br />

suns. <strong>The</strong> weakly glowing gas is<br />

peppered with many faint stars, making it almost<br />

indistinguishable from the patchwork Milky Way<br />

star fields permeating the region. I find that the<br />

best eyepiece combination for glimpsing it is a 22mm<br />

Panoptic and a 1.8x Barlow lens, which<br />

together yield 41x through the Genesis.<br />

Of course, finding the right magnification to<br />

bring out the nebula turns out to be a delicate<br />

balance between power and contrast. While the<br />

nebula is best seen at 41x it virtually vanishes at<br />

72x, though a filamentary "spike," which is a part<br />

of the Cave, does dimly stand out against the<br />

darkness. (This is the aforementioned ionization<br />

front.) Sweeping the telescope back and forth<br />

over the area will help the eye pick out the<br />

nebula's brightest (though low-contrast) glow. I<br />

find it at the center of the nebula, just west of the<br />

darkest part of the cavity, near a triangle of 9thmagnitude<br />

<strong>The</strong> <strong>Caldwell</strong> <strong>Objects</strong><br />

9<br />

suns. It is this 10'-wide area that I estimated to<br />

shine at an apparent magnitude of 10.0. A patch<br />

of dark nebulosity can be seen east of the triangle.<br />

Also, brief looks into the eyepiece will help more<br />

than a prolonged stare. But beware! It's easy for<br />

one's imagination to creep into the mind's eye.<br />

<strong>The</strong>re are many faint glows in the field, some of<br />

which I'm suspicious of— even though I included<br />

them in my drawing — because they tend to<br />

follow streams or clumps of faint stars rather<br />

closely. lust as some double stars (like M40)<br />

appear fuzzy at low power, so too do lines of<br />

stars and patches of the Milky Way. <strong>The</strong> use of a<br />

UHC filter should boost the contrast and bring<br />

out the nebula, which covers an area roughly 50<br />

light-years across. If you only suspect seeing the<br />

Cave Nebula, do not give up on it. Atmospheric<br />

clarity varies, so try on many nights. Once<br />

spotted, the nebula actually becomes easier to see<br />

on subsequent nights.<br />

Unfortunately, I was not able to see the<br />

entire dark mouth of the Cave in the 4-inch. Your<br />

challenge, then, is to determine the smallest<br />

aperture required to see this elusive feature<br />

47

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