Sky & Telescope - July 2023 - 29

NGC 6369 PHOTO: GARY IMM; FINDER IMAGE: POSS-II /
STSCI / CALTECH / PALOMAR OBSERVATORY
with my 7-inch Questar. Here I'll describe how I snagged eight
of my favorites, which are suitable for summer and autumn
nights. And I've observed all of them from my driveway.
I've selected this subset from my original surveys either
because I considered them interesting or simply because I
find them pretty. Some of the planetary nebulae were faint
fuzzies that taxed the limits of my instruments. A few were
so mundane it seemed that only professional astronomers
showed any interest in them. At least two turned out to be
exotic objects and even spectacular in images taken with
the Hubble Space Telescope (as on page 28). And three more
surprised me.
Besides my two Questars and several eyepieces, I also used
an O III filter at one time or another to observe these objects.
On several occasions I applied the handheld " blink " technique
to differentiate planetaries from dim stars. I also used
an eyepiece with an occulting bar to reduce glare if a bright
star was near my chosen target. In addition, the bar provided
a reference point during " blinking. "
Now, let's turn to our targets. I hope you enjoy them as
much as I did.
From Ophiuchus to Lyra via
Scutum
Perhaps the moniker " Lonesome " Ghost
would suit NGC 6369 better than its
accepted nickname, Little Ghost. On
my first visit to this planetary nebula
with my 3½-inch telescope, I noted
that it's practically the only luminous
object of interest in a 21′-wide
eyepiece field, save for 9.6-magnitude
HD 158233 located 5.6′ southsouthwest.
An O III filter enhanced the
planetary's 11.4-magnitude, 38″-wide
disk, but I couldn't make out that it was
annular, nor could I detect its 15.9-magnitude
central star. Some years later, I used the
7-inch at magnification 160× yielding a 17′-wide field,
which revealed the nebula's bluish color and profoundly dark
annulus (but I still couldn't see the central star). Look for
the planetary some 2° northeast of 3.3-magnitude Theta (θ)
Ophiuchi, just ½° northwest of 4.8-magnitude 51 Ophiuchi.
With the dense star clouds of Scutum as a backdrop, there
are few reference points for locating the 12.5-magnitude,
5″-diameter M 1-59. However, if you start at 4.7-magnitude
Delta (δ) Scuti and scan about 15½′ almost due east, you'll
land in its general area. A 25′-wide eyepiece field will reveal
the planetary's position between two 8.5-magnitude stars
that are just a bit less than 19′ apart in a north-northeast to
south-southwest direction. HD 172981, at magnitude 9.7, is
about halfway between these two stars, and the planetary is
2¾′ farther southwest along the same line.
Using the 7-inch at 212× yielded a 13′ field and with the
O III filter, the planetary presented a tiny, pale, bluish disk.
I couldn't detect a central star, and the edge of the disk
appeared smooth.
NGC 6765 is a fairly large planetary at 40″ across, but it's
dim (magnitude 12.9). It lies in Lyra about midway on a line
connecting Gamma (γ) Lyrae to Albireo in Cygnus. To help
you pinpoint it better, look for an isosceles triangle formed by
10th- and 11th-magnitude stars labeled in the image on page
30. This micro-asterism is relatively easy to see, and it fits
nicely into the 13′-wide field of my 7-inch telescope at 212×.
I used the O III filter after pre-focusing on a nearby star,
and I immediately became aware of something almost dead
center in the triangle. After several minutes of hyperventilation
and lots of imagination, I began to believe that the
planetary was actually there. Not only that but I then began
to imagine that the grayish nebula was elongated, and its
brighter end was pointed north-northeast almost directly
towards one of the triangle stars. It turns out that it wasn't
my imagination after all - I was really seeing NGC 6765!
To celebrate this find, I nudged my telescope about 4½°
NGC 6369
northwest to enjoy the satisfying sight of M57. We wish that
all planetary nebulae were as big, bright, and easy to see as
the Ring Nebula. But if they were, we'd probably
miss the thrill of finding something more
elusive like NGC 6765.
STARS LEAD THE WAY Find your way to
these targets by consulting the star chart on
pages 42-43 to locate the brighter stars discussed
in the text. Then, use the " pointer "
stars highlighted in the finder images here
to refine your search. Stellar magnitudes are
presented without the decimal point, and
dimensions are also given. North is up in all
images unless otherwise noted.
NGC 6369
HD 158233
96
20′ × 20′
sk yand tele scope .o r g * JULY 2023 29
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Sky & Telescope - July 2023

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