Sky and Telescope - November 2018 - 57
Going Deep by David Tosteson
Depth
Afield
Plunge into Pegasus and see
how many faint galaxies you
can spot with your scope.
M ASIL IM AGING TE A M
I
n the Greek myth of the white, winged
horse Pegasus and his rider, Bellerophon, the duo fight the Chimera and
perform other heroics. On their journey
to Mount Olympus, Zeus dismounts the
haughty equestrian but places ascending
Pegasus in the heavens, where he rises
in the clear autumn air as the thunderbolt-bearer of the gods. Crisp, dry
October evenings offer a fine time to
dig deep into the treasures of this relatively rich patch of sky. In the middle of
the month, the constellation's northern
region arcs nearly overhead at midnight.
The hours on either side of late evening
allow for a long and deep look into the
area around its brightest galaxy.
NGC 7331 is a 9.5-magnitude spiral
located 4.4° north of Eta (η) Pegasi.
The galaxy, first observed by William
Herschel in 1784, is 10.5′ × 3.5′ in size,
around 45 million light-years away,
and tilted 15° from edge-on. For many
years it was considered a "twin" to the
Milky Way Galaxy, but we now appreciate several differences between the two:
The Pegasus galaxy has no apparent
bar, the inner 5″ of the bulge counterrotates with respect to the disk, and it's
a flocculent, multi-armed spiral. Listed
at number 30 in the Caldwell Catalogue, it can be spotted in binoculars.
In progressively larger apertures detail
can be appreciated in its outer arms.
Images show a small, bright nucleus
and a bulge that extends just beyond the
edge of its minor axis, obscuring our
view of the more distant, eastern spiral
arms. At the 1996 Texas Star Party, my
25-inch reflector showed the galaxy to
be 11′ × 3′ with a 5′ bulge, with granular
detail in its outer arms.
p MAGNIFICENT SPIRAL NGC 7331, a galaxy in the northern reaches of the constellation Pegasus, is watched over by numerous smaller companions.
But this magnificent spiral doesn't
sit alone when observed in moderateto large-aperture instruments. To its
immediate east is a quartet of galaxies
nicknamed the Fleas. In "The Winged
Horse" (S&T: Nov. 2007, p. 74), the
sharp-eyed Sue French spotted all the
Fleas in her 4.1-inch refractor except
for magnitude-16.8 NGC 7336. Most
amateurs stop there, unaware of the
treasures populating the depths beyond.
Let's board a quest train to view the
distant galaxies of Pegasus.
Within a few years after Russell Croman took up astrophotography, he was
producing some of the finest images of
deep-sky objects. A visit to his website (www.rc-astro.com) displays the
marvelous detail he's captured in many
targets. His image of NGC 7331 in
Sue French's article caught my eye not
only for the almost three-dimensional
depiction of the large spiral, but also for
the galaxies layered at progressive dis-
tances. Scattered across the image were
dozens of galaxies ranging to beyond
magnitude 20. To me, it appeared like a
Hubble Deep Field for visual observers.
My friend and amateur astronomer
Larry Mitchell has spent thousands of
hours compiling the Mitchell Anonymous Catalog (MAC) of more than
125,000 objects, most of which are
rather faint galaxies surrounding bright,
well-known objects. In a hierarchy of
ascending difficulty for visibility in deepsky catalogs, MAC targets come after
Messier objects and those listed in the
New General Catalogue (sources prefi xed
with NGC) and other familiar catalogs,
such as the Uppsala General Catalogue
of Galaxies (UGC) and the Catalogue
of Principal Galaxies (PGC). In the case
of NGC 7331, Mitchell identified more
than 50 MACs in a 1° field centered
on the spiral. In addition to the MACs,
there is a slew of formerly "anonymous"
objects, presently being registered by
sk yandtelescope.com * N OV E M B E R 2 018
57
http://www.rc-astro.com
http://www.skyandtelescope.com
Sky and Telescope - November 2018
Table of Contents for the Digital Edition of Sky and Telescope - November 2018
Contents
Sky and Telescope - November 2018 - Cover1
Sky and Telescope - November 2018 - Cover2
Sky and Telescope - November 2018 - 1
Sky and Telescope - November 2018 - Contents
Sky and Telescope - November 2018 - 3
Sky and Telescope - November 2018 - 4
Sky and Telescope - November 2018 - 5
Sky and Telescope - November 2018 - 6
Sky and Telescope - November 2018 - 7
Sky and Telescope - November 2018 - 8
Sky and Telescope - November 2018 - 9
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