The Caldwell Objects

to the west by a row of similarly bright suns. The
galaxy looks somewhat like a ghost image of the
cluster, making me wonder why NGC 6939 is not
the Caldwell object.
But give the galaxy time — a lot of time.
Slowly the seemingly uniform circular haze takes
on a more elliptical form, oriented northeast to
southwest (like the cluster), with a sharp core.
Now relax for a moment away from the eyepiece.
Next, focus your attention on the galaxy's heart.
In time, the core should appear to be surrounded
by a tight, broken ring of light. That ring, in turn,
is surrounded by yet another concentric glow
whose jagged edges mark the beginnings of
spiral structure — the positions of those ghostly
density waves rolling through the galaxy like
ripples in a lake.
The Caldwell Objects
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(Imagine the sharp core as the stone dropped in
the water to create the ripples.) You can now use
your mind's eye and transform the innermost
ring into a dust-shrouded circle of star birth that
astronomers have discovered close to the
galaxy's nucleus. There, a fantastic episode of
intense star formation has been occurring for the
last 20 million years; probably it was triggered by
a rotating bar that has been detected at infrared
wavelengths.
NGC 6946 virtually vanishes at 72x, so users
of small or moderate-size telescopes will have to
be satisfied with what they can make out at low
power. Unfortunately, this requires a lot of
patience. But the effort will be rewarding as faint
details briefly float in and out of view. On the
other hand, if you own a large telescope, NGC
6946 should appear quite dramatic. Through her
20" f/4 reflector at 220x Barbara Wilson saw
several Η II regions in the four spiral arms. The
galaxy's 1'-wide core was very bright, and its
outer arms were apparent, especially to the east.
Had I stumbled upon this object in the 19th
century with a telescope as good as the Genesis
refractor — a very unlikely circumstance — I
would have likened it to a globular cluster at the
limit of resolution. William Herschel apparently
alluded to this aspect of NGC 6946 when he
wrote that "the nucleus seems to consist of stars."
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