WWW.ASTRONOMY.COM 49M81
To view our penultimate wonder, head
to the northwest section of the constel-
lation Ursa Major the Great Bear, where
you’ll find M81, one of the sky’s brightest
galaxies. It is located 2° east-southeast of
the magnitude 4.5 star 24 Ursae Majoris.
It glows at magnitude 6.9 and measures
24' by 13'.
German astronomer and celestial car-
tographer Johann Elert Bode discovered
this object December 31, 1774, so its
common name is Bode’s Galaxy. (He also
found the nearby irregular galaxy M82.)
French astronomer Pierre Francois André
Méchain independently discovered both
galaxies five years later and reported
them to Charles Messier, who added them
to his classic list.
Bode’s Galaxy glows brightly enough to
show up through binoculars, but the larger
the telescope you can point at it, the better.
Through an 8-inch scope, you’ll see a large,
bright central region surrounding the much
brighter core. Through a 12-inch instru-
ment, you’ll detect how the spiral arms
wind tightly around the core. The eastern-
most appears brighter. Unfortunately, you
won’t detect any dust lanes or star-forming
regions through amateur scopes of any size.
M81 is the brightest member of the M81
Group, one of the closest galactic groups to
our own Local Group. The M81 Group
contains about a dozen galaxies and lies
12 million light-years away. Other mem-
bers of this group include M82, NGC 2403,
NGC 2366, and NGC 3077.M31
Like The Outer Limits, I’ve saved the best
for last. The northern sky’s greatest galaxy
gets its familiar name from the constel-
lation where it resides, Andromeda the
Princess. This galaxy is the nearest large
spiral, and it sits at the far end of the Local
Group of galaxies. And in this case, near-
ness equals brightness: magnitude 3.4.
Observers have long described M31
as something other than starlike. Forinstance, in A.D. 964, Persian astronomer
Abd al-Rahman al-Sufi called it a “little
cloud” in his Book of Fixed Stars. German
astronomer Simon Marius (1573–1625) was
the first to study M31 telescopically. He
described it, “Like the f lame of a candle
seen through horn, and like a cloud con-
sisting of three rays; whitish, irregular and
faint; brighter toward the center.” Messier
cataloged the object on August 3, 1764:
“The beautiful nebula of the belt of
Andromeda, shaped like a spindle; it
resembles two cones or pyramids of light,
opposed at their bases.”
In 1888, British astronomer Isaac
Roberts became the first to photograph the
spiral structure of M31. In 1912, V.M.
Slipher first measured M31’s radial velocity
(the speed of a celestial object toward or
away from us). He found
its velocity far sur-
passed that of any
other object, and his
measurement helped
prove M31 lay far from
the Milky Way. In
1923, Edwin Hubble
measured a Cepheid
variable star in M31
and confirmed its
extragalactic nature.
Observers approach
the Andromeda
Galaxy in one of two
ways: Some opt for
low-power optics to
take in the entire view,
which includes M31’s
nucleus, dust lanes,
and two companion
galaxies, M32 and
NGC 205. If this is
your approach, try to trace M31’s full
length, which equals six Full Moons side
by side (185' by 75').
Other amateur astronomers eschew
wide-field views of the Andromeda Galaxy
in favor of greatly magnified looks at small
regions through large telescopes. If this
plan appeals to you, use as big a scope as
you can, and crank up the magnification to
300x or more. The central region will still
be featureless, but it will pay for you to
scan M31’s spiral arms for bright clumps,
which indicate star-forming regions.
Good luck on your voyage to [dramatic
pause] the outer limits.BOB FERAADAM BLOCK/MOUNT LEMMON SKYCENTER/UNIVERSITY OF ARIZONAMichael E. Bakich thanks Ken Murray of
Alhambra, California, for writing the email
that sparked his desire to write this story.M81