The Legendary Centaur
was a beast with the head
and torso of a man and the body of a horse. In Greek mythology,
centaurs were the only monsters of old capable of doing good deeds,
although some were rude, got drunk at weddings and celebrations,
and broke the furniture. One of the noble and wise among these
creatures was Chiron, son of Chronos and the ocean nymph Philyra.
He was a mentor to many of the gods and heroes of Mount Olympus
and the favorite teacher of both Apollo and Diana. The kindly
Chiron was accidentally wounded by a poisoned arrow shot by Hercules,
one of his pupils. On his death, Chiron was memorialized by Jupiter,
who placed him among the stars as the constellation Centaurus,
although some claim he is Sagittarius, the archer.
The constellation is a large southern one with only its northernmost
stars visible to those on the mainland of the United States. But
for people living in Hawai‘i Centaurus is one of the glorious
features of spring skies. The only constellation other than Orion
that has two first-magnitude stars, it is a star group that can
easily be visualized as the creature it represents, prancing toward
the east, over the Southern Cross, its forefeet studded with those
bright stars, Alpha- and Beta-Centauri. The brighter of these
two stars is a triple star system, a double that can be resolved
with a small telescope, plus a third member which was discovered
in 1915. This minor sibling in the Alpha-Centauri family revolves
about the others in a very large orbit such that for part of its
period it is the closest star to the Sun. It is thus named Proxima
Centauri. The proximity of the entire system was known as early
as 1839 when Thomas Henderson, director of the Cape Observatory
in South Africa, measured its parallax to be nearly one second
of arc (more exact measurements later brought this value down
to 0.76"). This confirms that the distance to the star is
4.3 light-years. Only a very few stars are located close enough
to us to make this direct method of triangulation, using the diameter
of Earth’s orbit as the base, practicable for judging stellar
distances.
There are no Messier objects in Centaurus, for Messier did not
observe from a latitude from which the constellation could be
seen. There are a number of objects there that would have made
his list, including the largest and richest globular cluster in
the entire sky, Omega Centauri. This was discovered to be a cluster
by Halley, who viewed it from St. Helena in 1677 (Latitude 16°S).
This marvelous photo of
the southern portion of Centaurus, together with Crux and parts
of Carina, Vela, Musca and Circinus, was taken on March 26, 1998,
by Axel Mellinger from the Cederberg Observatory in South Africa.
He used a Minolta 50-mm lens at f/4, with Kodak Ektapress Multispeed
PJM film.
At the left of the image Alpha and Beta-Centauri dominate, while
at the center is the Southern Cross, just below and to the left
of which lies the dark area known as the Coalsack. On the right
is the beautiful Eta Carina Nebula. Please find a remarkable collection
of Axel's work at his site: http://moore4.cchem.berkeley.edu/~axel/.
Another observer of the
wonders of Centaurus was Herschel. He was first to sketch the
curious galaxy known as Centaurus A. This is NGC 5128, referred
to as an astronomical mystery waiting to be solved. It is the
third brightest radio source in the sky, a giant spherical galaxy
encircled by a dark dust band.
On May 14, 1998, NASA released images of Centaurus A, showing
unprecedented detail in the dust lane. The Hubble Space Telescope's
Near Infrared Camera and Multi-Object Spectrometer (NICMOS) probed
deeper, piercing the dust and revealing two powerful radio jets
emerging from the core, which astronomers believe indicates that
a massive black hole lurks there.
This image and
others, together with a full description, can be found at http://oposite.stsci.edu/pubinfo/pr/1998/14/pr.html
Astronomers expected to
find a dusty disk of gas feeding the black hole and oriented perpendicular
to the jets, but instead they found a disk at a skewed angle.
Perhaps new material is falling toward the black hole from different
directions than before, creating the tilted disk that feeds into
a smaller, unseen disk with the proper orientation.
A number of multiple stars, clusters and galaxies are in the realm
of Centaurus, but because of their southerly position, they are
usually not prime targets for amateur stargazing.