Sky & Telescope - December 2022 - 57

Going Deep by Mel Bartels
The Clouds of Andromeda
A familiar object presents surprising new sights, if you view it carefully with the right equipment.
SHIMMERING SIGHT My 30-inch scope
reveals glorious detail in and around the Andromeda
Galaxy. Particularly striking to me is
the Andromeda Shelf, the nebulosity that loops
around M110. While the paddlelike extensions
at either end of the galaxy follow the warp of
the twisted spiral arms, they're also aligned
with the galactic cirrus that streams along the
galaxy itself. It's not clear to me if the paddles
are part of Andromeda, the cirrus, or both.
L
ook long enough with a wide-angle
telescope into the darkest skies and
you may see something astounding: The
sky background varies ever so slightly.
This isn't your imagination - it's
galactic cirrus. Comprising dust and gas
that's thrown far outside of the galactic
plane by supernova explosions, galactic
cirrus reflects the integrated light of the
galaxy like a ghostly apparition.
We can trace the first (recorded)
mention of galactic cirrus to William
Herschel, who concluded that, visually,
the sky " ground " varied. He compiled a
table of 52 " Nebulosities that have not
been published before " in the Philosophical
Transactions of the Royal Society of
London in 1811, which includes areas
of galactic cirrus. But it's only more
recently that the subject has been
studied in greater detail, starting in
the 1960s when American astronomer
Beverly Turner Lynds cataloged clouds
and nebulae that she identified on
Palomar Observatory glass survey plates.
Several amateur astronomers were also
intrigued by the topic and started imaging
galactic cirrus, including Steve Mandel
for his Unexplored Nebula Project.
I find it stunning to stumble upon
unexpected nebulosity - I've identified
and drawn more than 120 fields
of galactic cirrus clouds, mainly in the
northern spring sky. And now I'd like
to turn to a familiar target: Amazingly,
a thin veil of Milky Way galactic cirrus
encircles M31, the Andromeda Galaxy.
It might even be possible that the clouds
extend some 14° southeastward to M33,
the Triangulum Galaxy. I discovered
these clouds visually with my homemade
telescopes equipped with wide
fields of view at maximum exit pupil.
The Andromeda Galaxy
and Neighbors
In 2013, during first light with my
6-inch f/2.8 Newtonian with a true
field of view of 4.2° (for details see S&T:
Sept. 2014, p. 72), I pointed the scope at
the Andromeda Galaxy. Taking in the
entire object, I noted a warping of the
spiral arms, which appear to reach out
towards its southern satellite galaxy,
M32. A collision some 800 million years
ago between M32 and Andromeda may
have caused the warp, which I like to
call the Andromeda Twist. Scanning
back and forth across the galaxy with
my 30-inch f/2.7 (with a field of 1°),
the distortion of the spiral arms on
both sides of the nucleus was striking.
With the 6-inch, I also became
aware of indistinct nebulosity that
envelops Andromeda and then curves
around M110, the brightest and largest
of Andromeda's satellite galaxies. I particularly
enjoy showing fellow stargazers
the Andromeda Shelf, as I call this
nebulosity, in my wide-field telescopes
- to an experienced observer in dark
skies, the Shelf is rather bright.
Focusing on the satellites, M32 looks
small and featureless in the 30-inch.
This galaxy is stuffed with 400 million
stars yet is only 6,000 light-years
across. Unlike the main galaxy, M32
has no accompanying globular clusters
that would be accessible in large amateur
scopes. And astronomers are still
debating whether M32 is in front of or
behind the Andromeda Galaxy.
In contrast, M110 shows faint dust
lanes, and its elongated nucleus is at
a different angle to the fainter extensions.
M110 is warped, too! Through
sk yand tele scope .o r g * DECEMBER 2022 57
ALL DRAWINGS BY THE AUTHOR

https://skyandtelescope.org/

Sky & Telescope - December 2022

Table of Contents for the Digital Edition of Sky & Telescope - December 2022