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GlennLeDrew
professor emeritus
Reged: 06/18/08
Posts: 633
Loc: Ottawa, Ontario, Canada
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Re: Cave Nebula (Caldwell 9) finally saw a piece
07/28/08 08:09 PM
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The reason for the great difficulty in seeing Sh2-155 (the Cave) is that it's quite reddened by intervening dust. While I'm not certain, I am rather confident that there are no reflection components, or if there are, they're also significantly reddened so as to make visual observation problematic.
Why Mr. Moore included this challenging object defies any logic I can devise...
A more interesting (and at least easier) observation to be made is of the stellar association Cepheus OB3, to which the Cave is also associated.
Cep 3 is a fairly obvious enhancement of 6-9 mag. stars, 3.5 x 1.25 deg. in extent, oriented roughly NE-SW. The Cave lies at the SW end. The distance to Cep 3 is about 2,500 to 3,000 l-y.
The intervening dust renders many of the otherwise bluish O-type stars rather yellowish, and dims them by as much as a couple or even a few magnitudes. It's this extinction which subtracts much of the H-beta and O-III light of the associated nebulosity.
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Home-made 11X50 right angle bino, 8.1 deg. FOV
Modified 26X100 bino, 3.5 deg. FOV
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