Sky and Telescope - September 2017 - 43

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WHEN TO
USE THE MAP

Late July Midnight*
Early Aug. 11 p.m.*
Late Aug. 10 p.m.*
Early Sept. 9 p.m.*
Late Sept. Nightfall
*Daylight-saving time

alaxies in Pegasus, the Winged Horse, have
a certain reputation: They're challenging.
With famous members like Stephan's Quintet and
Einstein's Cross, you could be forgiven for thinking
that only observers with large scopes need apply.
There's at least one exception, however: NGC
7331 (Caldwell 30), a big, beautiful spiral galaxy in the
northern reaches of the constellation. To find NGC
7331, draw a line from Mu (μ)
μ Pegasi to Eta ((η)
η) Pegasi
and straight on for another 4½°. The galaxy also forms
the northeastern corner of an imaginary right triangle
with Eta Peg and Pi2 ((π2) Peg.
With a visual magnitude of 10.4, NGC 7331 won't
necessarily be an easy catch, especially in lightpolluted skies. But observers in only moderately dark
skies have spotted it with 7×50 binoculars. So far I've
needed at least 10×50s to pull it out, and 15×70s are
better still - but when is that not true? It helps that
the galaxy is big, 10′ × 4′, which is comparable to the
largest Virgo galaxies. The large apparent size (as
these things go) corresponds to ample proportions in
real life. With a diameter of 130,000 light-years, NGC
7331 is larger than our own Milky Way.
NGC 7331 isn't just unusually bright for a Pegasus
galaxy, it's also an astrophysical oddball. Several
recent studies suggest that the galaxy's central bulge
rotates in the opposite direction of the spiral arms.
I have one more bit of homework for you: Go
online and find a high-res photo of NGC 7331. One
of my favorite was taken by Vicent Peris at the Calar
Alto Observatory in Spain - it looks like the cover of
a sci-fi novel, but it's real. How wonderful that we can
plumb the depths of intergalactic space with handheld instruments.

¢ MATT WEDEL likes to kick back with his binoculars on a driveway in Claremont, California.
s k y a n d t e l e s c o p e .c o m

* SEPTEMBER 2017

43
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Sky and Telescope - September 2017

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