101 SKY OBJECTS
WWW.ASTRONOMY.COM 72 The Bug Nebula
Amateur astronomers named the Bug Nebula (NGC 6302) for its insectlike shape. But because the
Bug’s apparent size is only 2', that shape is all they saw. Recent pictures taken with the Hubble Space
Telescope have revealed much more detail. Now NGC 6302 is often called the Butterfly Nebula.
Whatever name you give it, NGC 6302 is on a number of top 10 lists — no surprise, considering
its visual magnitude of 10.1 makes it one of the brightest planetary nebulae known. It’s also among
the most massive. And its central star has a surface temperature greater than 450,000 degrees
Fahrenheit (250,000 degrees Celsius), making it one of the hottest stars in the universe.
That central star, by the way, wasn’t discovered until 2009. Astronomers didn’t detect it because it’s
so hot that most of its output is ultraviolet radiation, which the surrounding cloud of gas absorbs and
then reemits as visible light. The lack of visible light coming from the star, coupled with its bright sur-
roundings, made spotting it difficult. It wasn’t until astronauts installed the Wide Field Camera 3 onto
Hubble that researchers finally saw it.
American astronomer Edward Emerson Barnard discovered NGC 6302 through a 5-inch refractor
in 1880. The planetary lies some 3,400 light-years away in the constellation Scorpius. To find it, point
your telescope 3.9° west of magnitude 1.6 Shaula (Lambda [λ] Scorpii).
If you observe NGC 6302 through an 8-inch telescope with an eyepiece that magnifies between
50 and 100 times, it looks like a galaxy that stretches east-west and is four times as long as it is
wide. At powers above 150x, you’ll be able to see the two lobes on either side of the core. The one
on the western side is easiest to see. It has a tapered end. The faint arm to the east is a more difficult
catch. — M.B.KFIR SIMONWith the possible exception of the Big Dipper, the
Southern Cross ranks as the sky’s most familiar asterism
(a recognizable group of stars that is not a constella-
tion). Indeed, its three brightest stars are among the
25 brightest in the whole sky. This stellar pattern is
so famous that five countries depict it on their flags:
Australia, Brazil, New Zealand, Papua New Guinea,
and Samoa.
Mariners plying southern waters have used the
Southern Cross as a direction marker for centuries. Its
long axis points to the South Celestial Pole, which is
handy because, unlike in the Northern Hemisphere, no
bright star lies anywhere near that spot. Specifically,
a line drawn from magnitude 1.6 Gacrux (Gamma [γ]
Crucis) through magnitude 0.8 Acrux (Alpha [α] Crucis)
and extended 25° will lead an observer close to the
South Celestial Pole.
Officially, the Southern Cross is the constellation
Crux, a star pattern picked out by early European explor-
ers. Crux ranks as the smallest of the 88 constellations,
covering a paltry 68.45 square degrees. That area is
only 0.166 percent of the sky. Because it contains several
bright stars, however, it tops the list in terms of overall
brightness, which is the number of visible stars in a con-
stellation divided by the constellation’s area in square
degrees. That value for Crux is 29.2, far surpassing the
second-place finisher for overall brightness, Corona
Australis, which has a value of 16.4. — M.B.3 The Southern Cross
CHIRAG UPRETI1 Centaurus A
Centaurus A (NGC 5128) is a standout object
for Southern Hemisphere observers. NGC
5128 is often called the Hamburger Galaxy
because of the two regions of stars (the bun)
that surround a dark dusty lane (the burger).
And it’s a heck of a meal: A mere 12 million
light-years away, Centaurus A has a diameter
of about 60,000 light-years.
Scottish astronomer James Dunlop
discovered NGC 5128 in 1826 using a 9-inch
reflecting telescope in his observatory in
Parramatta, New South Wales, Australia.
Astronomers gave it the catalog name
Centaurus A because it was the first radio
source discovered in the constellation.
Both NGC 5128’s appearance and its
radio emission have their roots in a galactic
collision. The main body of Centaurus A —
a giant elliptical galaxy — is absorbing a
smaller spiral galaxy. The two objects collided
more than 200 million years ago, creating
large regions of star formation. This collision
also probably aided the growth of the super-
massive black hole in the center of the galaxy.
Current estimates of its mass put it in the
range of 55 million times that of the Sun.
To find NGC 5128, aim your telescope 4.5°
due west of magnitude 3.5 Mu (μ) Centauri.
Through small scopes, the galaxy appears
round with a wide dark lane cutting it in half.
This lane gets wider on both ends. Through
14-inch or larger instruments, you should
see a thin wedge of light shining through the
lane’s western end. — M.B.GABRIEL SANTOS