The Caldwell Objects

streamers begin to appear, but they will vanish
like celestial ghosts under a direct gaze. The
knots are the most mysterious features because
they waver in and out of view in the 4-inch,
leading even an astute observer to question their
reality. The million-dollar question is: Does TY
Coronae Australis look less stellar than its
magnitude-7.2 companion? Perhaps it is
immersed in a thicker bed of dust and gas than
its companion rests in. What do you think?
Finally, onto our Caldwell target. A very faint
petal of nebulosity extends from NGC 6726-7 to
the southeast and tapers to a point, like one of
those stringy coronal streamers seen during a
total solar eclipse. This delicate tendril points
directly to our target, NGC 6729, just 5' away. At
23x NGC 6729 appears fuzzy, but at such low
magnification it's hard to tell if this is true
nebulosity because its bright "head" (R Coronae
Australis) is only 1.3' northwest of yet
The Caldwell Objects
68
another nebulous variable star, Τ Coronae
Australis, and the two stars make a fuzzily close
pair. In the 4-inch at 72x NGC 6729 is the least
interesting object in the area, at least visually. It
shows some definite haziness that extends
toward Τ Coronae Australis to the southeast, but
that's all. High power is required to make out any
detail. Once you know what you're looking for,
however, NGC 6729's cometlike nature becomes
apparent. Or so it did in September 1996, when I
observed this Caldwell object; the nebula may
have changed since. At high power an obvious
central bar pointed directly toward Τ Coronae
Australis. A fan of material can be seen on either
side of the bar. While NGC 6726-7, with its
double star and nebulosity, reminds me of M78
in Orion, smaller NGC 6729 looks like Hubble's
Variable Nebula in Monoceros, and photographs
of the entire region recall the Pleiades. What a
fascinating part of the sky!
Certainly amateurs looking for a long-term
project can focus on the variable nature of NGC
6729. CCD owners should first try imaging NGC
6729 each month, then, once a year has passed,
create a movie from the successive images. This
should show how the nebula changes with time
and may well capture the interest of some
professional astronomers.
I made a magnitude estimate for NGC 6729
at 23x and got about 9.5. See how this compares
to your own estimate. For a visual description of
the fantastic globular star cluster NGC 6723 in
Sagittarius see page 442 in the next chapter. I
searched for the globular with the naked eye but
couldn't see it without optical aid. See if you
have better luck. I think it can be done.
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