101 SKY OBJECTS
WWW.ASTRONOMY.COM 96 The Rosette Nebula (^)
Observers and astroimagers usually think of the magnificent
Rosette Nebula as a single deep-sky object. But actually, this
combination of a star cluster and nebula has five separate entries
in the New General Catalogue: NGC 2237, NGC 2238, NGC 2239,
NGC 2244, and NGC 2246. And although they all lie within the
constellation Monoceros the Unicorn some 5,200 light-years away,
they weren’t all discovered at the same time.
The beautiful open cluster NGC 2244, which lies at the center
of the nebulous complex, was found by English astronomer John
Flamsteed in 1690. Then, in 1830, John Herschel discovered the first
nebulous region, NGC 2239. Next up was NGC 2238, discovered in
1864 by German astronomer Albert Marth. To complete the picture,
7 NGC 7331
Deep-sky objects have some creative
nicknames, but what’s up with the
Deer Lick Group? In the 1980s, amateur
astronomer Tom Lorenzin was observing
in the mountains of North Carolina, at the
Deerlick Gap Overlook. Because his view
of NGC 7331 and its surrounding galaxies
was so memorable, he christened them
the Deer Lick Group.
William Herschel discovered NGC 7331
in 1784. This galaxy is a pure spiral, nary
a bar in sight. It lies in the constellation
Pegasus the Winged Horse about 4.4°
north of 3rd-magnitude Matar (Eta [η]
Pegasi).
The Deer Lick Group contains four
other galaxies: NGC 7335 (magnitude
13.4), NGC 7336 (15), NGC 7337 (15.2), and
SERGEY TRUDOLYUBOVNGC 7340 (14.9). In comparison, NGC 7331
PATRICK A. COSGROVE
BERNARD MILLER
American astronomer Lewis Swift discovered NGC 2237 in 1871 and
NGC 2246 in 1885.
You won’t have any problem seeing NGC 2244. If your observing
site is dark, a 4-inch telescope will reveal 25 stars in an oval region
that stretches northwest to southeast. It’s a bright oval, too. Six of
the stars are brighter than 8th magnitude. Move up to an 11-inch
scope, and the background star count will surpass 100. Whichever
scope you choose, start with an eyepiece that has a true field of
view between ½° and 1°.
Two things will help you observe the four nebulous regions that
surround NGC 2244: low power and a nebula filter. A magnification
around 50x will give you a wide field of view, and the filter will dim
the cluster’s stars. — M.B.
glows at magnitude 9.5. But these fleas,
as they are called, aren’t actually fainter
or smaller than the main galaxy. They’re
simply much farther away.
While NGC 7331 lies about 40 million
light-years from Earth, the four other
members are between 290 million and
370 million light-years away. So, calling
this gathering a group is correct only in
an apparent sense. In fact, none of the
fleas are even gravitationally bound to
each other.
From a dark observing site, most
observers can spot NGC 7331 through
50mm or larger binoculars. An 11-inch
telescope and a magnification of 200x
will reveal a bright core surrounded by a
soft glow three times as long as it is wide.
You’ll also just barely see three of the fleas
as an equilateral triangle east of the main
galaxy. — M.B.