The Caldwell Objects

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lies just north-northeast of the illuminating 9thmagnitude
star. With a glance in the Genesis, I
initially mistook this circle of light for the Bubble,
especially since a patch of dark nebulosity
occupies its center. But it is not the Bubble. (It is,
however, the portion of NGC 7635 that shines at
10th magnitude. Also note that I have
exaggerated the Bubble's northern rim in my
drawing; otherwise it might not have been reproduced.)
The Bubble, in fact, is the smallest of
three bubbles associated with the central star.
Unfortunately the Bubble is not a feature to
be glimpsed casually through small telescopes. It
is not visible in its entirely in the 4-inch Genesis
(though plenty of the surrounding nebulosity is).
Christian Luginbuhl and Brian Skiff could not see
it through a 6-inch telescope, saying that even
NGC 7635 was
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"very faint and barely discernible." No, it takes
large apertures (and perhaps a nebula filter) to
see the Bubble well. Using a 13.1-inch f/4.5
reflector at 47x from Columbus, Texas, Barbara
Wilson not only discerned the Bubble, finding it
"lovely and delicate," she also saw a bright
greenish tint to it — without a filter. Of course,
nothing can beat a view of the Bubble through a
really large telescope, like the view I enjoyed
during one Winter Star Party in the Florida Keys
through Tom and Jeannie Clark's 36-inch Yard
Scope (now owned by Astronomy To Go). That
night the full ghostly loop, supported by the
amorphous greenish glow of NGC 7635 stood out
sharply against the scintillating backdrop of the
Milky Way. In fact, the Bubble and its surrounding
nebulosity looked rather like a wad of
bubble gum stuck to the underside of a table.
Deep-Sky Companions: The Caldwell Objects