The Caldwell Objects

as strongly energized as would be expected. This
fact suggests that some of the ultraviolet
radiation from the very hot central star is being
absorbed by a shield of dust between the star and
the glowing nebula. The dust could have been
created when the central star's fast wind (racing
at speeds of about 1,800 km per second) collided
with the much more slowly expanding planetarynebula
shell (which crawls along at a mere 40 km
per second). Earlier mass-ejection events could be
responsible for the nebula's outer shell and other
peripheral features.
Seen through a small backyard telescope,
NGC 40 is a visually unimposing sight. The
nebula's compact disk can be found about 5½°
southeast of magnitude-3.2 Gamma (γ) Cephei,
and midway between, and slightly west of, two
roughly 9.5-magnitude stars. Through the 4-inch
at 23x, NGC 40 appears virtually stellar;
The Caldwell Objects
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this is not surprising, considering that the
magnitude-11.6 central star is nearly twice as
bright as the surrounding nebula. Increasing the
magnification to 72x helps separate the
diminutive nebula from the star; the dark cavity
between the central star and its shell is barely
discernible. With averted vision and prolonged
effort on an observer's part, the nebula looks
distinctly oval, oriented southeast-northwest, and
a 13.5-magnitude star pops into view just 1¼’ to
the nebula's southwest. High power brings out a
beaded nature to the ring, which has two
prominent knots: one to the southeast, the other
to the northwest. (The other beads are rather
amorphous.) The positions of the two brightest
beads correspond well to the luminous arcs that
show up in photographs of the nebula's truncated
ring. Magnifications in excess of 200x should
make these arcs stand out more clearly.
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