The Caldwell Objects

Observatory, England) still lists a possible
supernova remnant in A Catalogue of Galactic
Supernova Remnants, dated 1998. Although the
jury is still out on the origin of the outer infrared
nebula, it's safe to say that to see the Crescent
Nebula is to see the results of several stages of
energetic stellar activity.
Through 7x35 binoculars the nebula's
environs look hazy, but since the remnant lies in
a patchy, star-rich area of the Cygnus Milky Way
and slices through a diamond of 7th- and 8thmagnitude
stars, there is no way to confirm that
this visual impression really constitutes a
detection of the Crescent. On the clearest of
nights the oval shape of NGC 6888 can be
discerned — just barely — at 23x through the 4inch
refractor. The nebula's brightest segment is a
sharp needle of light extending southwestward
from the diamond's
The Caldwell Objects
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brightest star (HD 192182, a 7th-magnitude Gtype
star with an 11th-magnitude companion).
So sharp is this needle when seen at low power
that I initially mistook it for some weird diffraction
spike — until I realized I was using a highquality
refractor that causes no such artifacts. In
the 4-inch the star and the spike look like a
distant quasar with a jet shooting outward.
The view looks much the same at 72x. But a
concentrated effort (remember to breathe often
and to look away from the eyepiece every now
and then) reveals a patchy extension of very dim
light continuing to the southwest before it gently
curves southeast. Interestingly, I found this
nebulous segment consistently easier to see than
the curved remnant to the northeast, even though
the latter looks brighter in photographs. I
attribute this paradox to the fact that the nebula's
northeastern section lies close to two of the
diamond's stars and, at modest magnifications,
the glare of these bright stars diminishes the
view. By contrast, the southwestern extension,
while fainter, lies in a region free from such
troublemakers.
The ultimate visual challenge is to close the
loop on the southeastern side of NGC 6888.1 did
this by using low power and averted vision. Take
plenty of time to confirm what you see. I find
that, with time, the thin vapors waver in and out
of view. Also, if you compare the brightness of
the shell's inner edge with that of the
surrounding region, it should become clear that
your eyes are picking up faint emissions from
excited gases. This glow is more prominent on
the southeastern side.
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