17 NGC
1275
NGC 1275, often referred to
as Perseus A, is the bright-
est member of the Perseus
galaxy cluster. It lies roughly
225 million light-years
away and has a diameter
of slightly more than 100,
light-years. The A part of
its designation means the
object is a strong source of
radio emission.
NGC 1275 is considered a
Seyfert galaxy. Each member
of this class of active galax-
ies has a brilliant quasarlike
nucleus, but not so bright
that it drowns out the rest of the galaxy.
In addition to being a strong radio source, NGC 1275 is also a strong emitter of X-rays.
The source of this radiation is the center of the galaxy, where a supermassive black hole
with a mass some 800 million times that of the Sun gorges itself on gas. The friction and
other forces produced by the gas as it spirals into the black hole generate X-rays.
The Perseus galaxy cluster, also known as Abell 426, is part of the Pisces-Perseus
Supercluster. This chain of galaxy clusters stretches more than 40° across the sky. To find
the Perseus galaxy cluster, look 2° east of Algol (Beta [β] Persei). Through a large amateur
telescope, several of its galaxies — all ellipticals — appear bright, small, and nearly circu-
lar. Don’t confuse NGC 1275 with NGC 1272, a similar galaxy just 5' to the west. NGC 1272
is ever-so-slightly brighter.
Through a 10-inch telescope, you’ll spot a dozen galaxies in a field of view 1° across.
Most lie south and west of NGC 1275. Here’s a region of sky where increased aperture
really pays off. As you look through larger telescopes, you’ll see more galaxies, and the
ones you’ve already spotted will show a bit more detail — as much as ellipticals can
show, anyway. — M.B.
18 Barnard’s Galaxy
Barnard’s Galaxy (NGC 6822) was discovered by American astronomer Edward Emerson
Barnard through a 6-inch refractor in 1881. You’ll find this object in Sagittarius, 1.5° north-
northeast of 5th-magnitude 55 Sagittarii.
NGC 6822 is an example of a dwarf irregular galaxy. Barnard’s Galaxy was the first gal-
axy beyond the Magellanic Clouds for which astronomers calculated a distance. In 1925,
American astronomer Edwin Hubble used Cepheid variable stars within it to estimate its
distance at 700,000 light-years. The current best number, however, is 1.5 million light-years.
NGC 6822 glows softly at magnitude 8.1 — which is actually pretty bright for a galaxy.
Unfortunately, that light spreads out over an area 16' by 14', which is 30 percent the area of
the Full Moon. That makes its overall surface brightness low. So, whichever telescope you
use, start with the eyepiece that gives you the widest field of view. You’re looking for a dim
haze roughly twice as long as it is wide.
Large scopes will let you see several star-forming regions at the northern end of the
galaxy. The best
way to spot them is
through a 14-inch
or larger scope
used in conjunction
with a nebula filter.
Without a filter,
look for a slightly
brighter streak of
stars along the
galaxy’s long axis.
You might even see
some single super-
giant stars — these
are recognizable by
the grainy appear-
ance they lend the
galaxy. — M.B.
19 The Orion Nebula
Of all the deep-sky objects visible from mid-
northern latitudes, the Orion Nebula (M42) is by
far the most spectacular. To the unaided eye, it
faintly shines as the middle star in Orion’s Sword,
dangling below the three iconic stars of the
Hunter’s Belt. Johann Bayer christened it Theta
(θ) Orionis in his Uranometria atlas of 1603. But
neither he nor anyone else suspected its true
nature before the invention of the telescope.
We now know that the Great Orion Nebula is
a mammoth swath of ionized hydrogen gas and
dust — also known as a Hydrogen II (HII) region
— which makes it the sky’s best-known example
of an emission nebula. You can think of it like a
stellar incubator: Astronomers estimate at least
1,000 stars lie within it, veiled by opaque dust
and only unlocked with infrared imagery.
The Orion Nebula is an amazing sight through
all telescopes and binoculars. Even the smallest
binoculars reveal it as a misty glow around
Theta. But Theta isn’t really a single star; it’s
instead a pair of stars, Theta^1 and Theta^2 Orionis,
immersed in the cloud. Take a closer look and
you will see that Theta^1 is also not a single star
but instead a family of four suns neatly gathered
in a trapezoid pattern called the Trapezium. The
stars are designated A, B, C, and D, ordered
according to their location. The brightest of the
bunch is magnitude 5.1 Theta^1 C, which marks the
trapezoid’s southern corner.
Telescopes expose some of the nebula’s amaz-
ingly intricate details. Its curved swirls reaching
to the south are reminiscent of a cupped hand
grasping outward. Theta^1 Orionis also shines near
a distinctive silhouette known as the Fish’s Mouth,
which is formed by an area of dark nebulosity
standing in front of a brighter region beyond.
Just north and slightly east of M42 is a second,
much smaller tuft of nebulosity cataloged as
M43. Despite their distinct designations, M
is actually an extension of the Orion Nebula. It
only appears separate because a stretch of dark
nebulosity slices between the two. — P. H.DAN CROWSONJOHN CHUMACK JOHN CHUMACK