The Caldwell Objects

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NGC 7023 lies about 3½° southwest of Beta
(β) Cephei, or Alfirk, a quasi-Cepheid
variable star that pulses between magnitude
3.2 and 3.3 about every 4½ hours. (Alfirk is
also a nice double star, first noted by F G. W .
Struve in 1832, with an 8th-magni-tude
companion 13" distant.) The nebula, whose
brightness I estimated at magnitude 7.7,
surrounds a 7th-magnitude star (HD 200775),
and both can easily be detected in binoculars.
(Use averted vision to note the extended size
of that star compared to others in the field.) In
the 4-inch at 23x the star and nebula are quite
distinct, looking like a lamp seen through a
window moist with breath. With direct vision
the nebula measures a few arc-minutes in
diameter and looks irregularly round.
Under averted vision, however, the nebula swells
magnificently to a diameter of 10'. A quick glance
out of the corner of one's eye makes the nebula
look like a chiffon skirt suddenly puffed out by a
gust of wind. (Try the same with any other
similarly bright star in the field, and they will all
remain skirtless.) By the way, estimating the
nebula's brightness required some mental
gymnastics, namely psychologically removing
the 7th-magnitude star from view to concentrate
solely on the glow emanating from the nebula.
At 72x NGC 7023 displays some arcing bands
of nebulosity, knots (or faint stars embedded in
the glow), and sharp streamers. Most noteworthy
is a bar of light (oriented roughly north-south)
that slices through HD 200775. The ends of the bar
curve away in opposite directions, so the material
there seems to fan out like the spray from a twopronged
lawn sprinkler. Another weaker
streamer jets off the star to the north-northwest.
The full glory of
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this object is revealed at higher powers and with
averted vision. At 189x HD 200775 looks like a
topaz stone that has been hastily woven into a
spider's gossamer web. The nebula's densest
regions (the spiral-like arms) have a feathery
quality to them, while the remainder of the cloud
has a stringy texture reminiscent of the fibers in
high-quality paper. Prolonged study will bring
out the nebula's faint, hollow lobes extending to
the west and east.
Although reality dictates that we are seeing
the passive reflection of starlight by interstellar
dust within the nebula, it is not difficult to
imagine a more exciting, though fanciful, drama
unfolding before our eyes. Given NGC 7023'
central star, bright spiral twists, and ballooning
lobes, one could imagine that the star had
experienced a violent novalike explosion that
tossed out arcs of matter while shock waves
plowed through the surrounding interstellar
medium to form the lobes. But the prosaic truth is
that NGC 7023 is a prototypical reflection nebula
— one of the most extensively studied. It was one
of the first regions where
Deep-Sky Companions: The Caldwell Objects