101 SKY OBJECTS
23 M
The Southern Pinwheel Galaxy is a celestial treat for those who can see
it. This galaxy measures 14' by 13'. M83 also is bright at magnitude 7.5,
making it the eighth-brightest galaxy in the sky. Its distance certainly plays
a factor in both of these traits; the Southern Pinwheel Galaxy lies a mere
14.7 million light-years away.
Using a ½-inch refractor, French astronomer Nicolas Louis de Lacaille
discovered M83 in 1752. Charles Messier added it to his now-famous
catalog in 1781.
M83 is the second-brightest member of a collection of more than a
dozen galaxies called the Centaurus A/M83 group. As you may have
guessed, the other notable (and slightly brighter) object in this group is
Centaurus A (NGC 5128; see #1). Gravitational interaction in the past billion
years between M83 and the nearby dwarf irregular galaxy NGC 5253 has
triggered considerable star formation in each.
Despite so many galaxies in one area, M83 lies in a region of the night
sky short on bright stars. The nearest reasonably bright star, 1 Centauri,
glows at magnitude 4.2 and lies 3.7° south-southeast. Alternatively, you
can find M83 9° northwest of magnitude 2.1 Menkent (Theta [θ] Centauri).
From a dark site, the galaxy is pretty easy to sweep up using binoculars.
The Southern Pinwheel Galaxy appears nearly face-on, so you’ll see its
spiral structure through telescopes with apertures as small as 6 inches.
The core is petite and round, and the bar extends to the northeast and
southwest. Through 12-inch and larger scopes, you’ll see large clumps of
stars and star-forming regions along its arms. — M.B.
22 The Tarantula
Nebula
One of the sky’s standout objects is the
Tarantula Nebula, also known as the True
Lovers’ Knot, Caldwell 103, and 30 Doradus.
At the center of this HII region (a cloud of
ionized hydrogen) is the massive open cluster
NGC 2070. It’s the central group of ultrahot
stars in this cluster that produces the ultraviolet
radiation that makes the nebula glow.
It’s too bad that most amateur astronomers
living in the Northern Hemisphere haven’t
observed the Tarantula Nebula. Although it
lies 160,000 light-years away in the Large
Magellanic Cloud (see #80), this object looks
great through any telescope. Sporting a true
diameter of more than 1,800 light-years, the
Tarantula would appear some 25° across if it
were as close as the Orion Nebula (M42; see
#19). At that distance, its overall brightness
would top that of Venus, and it would even
cast shadows.
NGC 2070 is a young open cluster some
astronomers categorize as a super star cluster.
Such objects are brighter and more mas-
sive than the run-of-the-mill open clusters
we see elsewhere. But it’s really the central
16 light-year-wide region of NGC 2070 that
stands out. Listed in the Radcliffe Observatory
Magellanic Clouds Catalogue as R136, this is an
amazing starburst region. Many of its 72 stars
are among the most massive, brightest, and
hottest stars known.
R136 is easy to spot through a 4-inch scope
as a 1'-wide region. The same instrument will
reveal a few gaseous loops and filaments in the
nebula. The longest starts at the cluster’s cen-
ter and stretches 7' to the south. Then it curves
east and finally northward. Look to the east of
FERNANDO OLIVEIRA DE MENEZESR136 for two easy-to-see dark bays. — M.B.MAICON LOPES NUNES