Which is the one star pattern that "stands out" among all the others?
Just about every guide on astronomy and stargazing will list Orion as number one. But perhaps there might be a bias, since most Northern Hemisphere observers are only familiar with the stars of the Mighty Hunter and his retinue and not with other areas that are beyond their realm of visibility.
A case in point: This month, lying just above the southern horizon as darkness falls is a bright complex of stars stretching along the southern Milky Way. They include the constellations of Centaurus, Lupus and Crux — the Centaur, Wolf and Southern Cross, respectively. And hidden from view for most of us in the United States just might be the most superb part of the sky for naked-eye observers: the Southern Cross and its brilliant guardian stars to the east, Hadar and Rigel Kentaurus.
Centaurus is one of those few non-zodiacal constellations whose name is familiar to a wider circle of science buffs. This is due to its brightest star, Rigel Kentaurus, which is more popularly known as Alpha Centauri, which, along with its faint red-dwarf companion, Proxima, is the nearest star system to us, a mere 4.3 light-years away. It is certainly rather odd that this star is better known by its Greek letter designation than its proper name. And not far from Alpha is Beta Centauri, better known as Hadar. This pair of bright luminaries act as pointers, directing you straight to Crux, which itself contains two first-magnitude stars.
There is so much jammed in to this relatively small region of the sky: four first-magnitude stars, a rather bright section of the Milky Way and a conspicuous dark "hole" embedded within it composed of interstellar dust situated immediately adjacent to Crux — the so-called "Coal Sack." Those who are fortunate enough to have seen this region high in the sky, as I did back in 1986 when I led a Halley's Comet tour (opens in new tab) to the Chilean Andes, will readily agree that Orion is a mere runner-up.
Centaur of attention
Surrounding Crux on three sides is the large, bright constellation of Centaurus, which represents a centaur — the mythological creature that is half man, half horse. Check out a half dozen different star guides or constellation books, and each one will trace out Centaurus in a different way. It's a relatively formless star pattern, and its stellar sprawl is virtually indistinguishable from the second- and third-magnitude stars of neighboring Lupus, the Wolf.
In order to demonstrate just how the Centaur and Wolf are so closely entwined, there is an attractive pair of third-magnitude stars situated where these two constellations meet: Beta Lupi and Kappa Centauri. The official boundary between Lupus and Centaurus runs between these stars, separated by just 62 arc minutes. They provide an excellent indicator of how large a degree is in the sky. If you locate them, consider that two full moons could readily fit between them. (One degree is composed of 60 arc minutes. For perspective, your clenched fist held at arm's length covers about 10 degrees of sky.)
On many of the old-time star atlases that depict the constellations as allegorical pictures, Centaurus is usually shown impaling the Wolf on a long spear. In much the same way that Ophiuchus (the Serpent Holder) is physically holding two halves of Serpens (the Serpent) and is often pictured as one large single complex star pattern, the same might be said for Centaurus and Lupus.
And in much the same way that Scorpius, the Scorpion had his claws "clipped" to form Libra, the Scales, Centaurus lost its hind feet in modern times to form Crux.
A poetic fabrication
Who invented the centaurs? Homer, presumed author of the "Iliad" and the "Odyssey," and Hesiod, an ancient Greek poet, described them as humans, albeit beastly ones. Some 200 years later, the Greek lyric poet Pindar does describe them as quite different than us, but he was much given to embellishing the subjects of his narrative odes, of which some 40 have been preserved.
As unique a creature as a centaur was, Centaurus is one of two such horse-man combos in the night sky. The other — certainly far better known — is the zodiacal constellation of Sagittarius, the Archer. These centaurs held a very special place in Greek mythology and were said to possess an amazing range of abilities, both physical and mental. They were the ultimate hunters and warriors, far more efficient than men on horses, combining the skills and speed of both.
One reasonable explanation for the origin of the idea of a creature with a horse's body and legs and a man's head, arms and trunk is found in a fairly common expression: "He rides a horse as though he were a part of it." Possibly some early Greek tribe's first sight of enemies on horseback accounts for this creature's invention, as an excuse for having lost a battle.
Hence Sagittarius is traditionally represented carrying a bow and arrow. Centaurs were also regarded as quasi-deities who had certain godlike qualities such as immortality.
Related: Constellations of the western Zodiac
Who was Centaurus?
The stars of Centaurus are believed to represent Chiron, who was mentioned quite often in Greek mythology. Unlike the other centaurs, who were brutal and monstrous creatures, Chiron was extremely wise and gentle and tutored such mortals as Jason, Hercules and Aesculapius, the healer; the latter two later were immortalized as constellations. Hercules accidentally wounded Chiron, who was in great pain but unable to die because he was immortal, so he begged the gods to put an end to his suffering. Zeus finally allowed Chiron to die, and also placed him among the stars.
Some say that Sagittarius is identified with Chiron. However, Sagittarius was more of a warrior, depicted (as we have already noted) with a drawn bow and arrow, which simply was not in character with Chiron. Others say that Chiron himself created the constellation of Sagittarius, to guide Jason and the Argonauts as they sailed on the great ship Argo.
Some final thoughts
For those who live as far south as the southernmost parts of Texas and Florida, this is the time of the year to try and get a glimpse of Crux and the famous Centaurus pair at around 9:30 p.m. local daylight time. A clear night and a low southern horizon are needed. Hawaiians and our friends in Puerto Rico and the adjacent Caribbean islands can find them more readily.
The Southern Cross is now pictured on the flags of several countries. It is the smallest, in area, of all 88 constellations. Its two bluish first-magnitude stars are called Acrux and Becrux.
The Dutch astronomer Petrus Plancius was the first to recognize Crux as a separate constellation on his 1598 star globe, but for nearly a century it had been shown superimposed on the feet of Centaurus. The Italian explorer and navigator Amerigo Vespucci was the first of the Europeans to see the "Four Stars," (opens in new tab) as he so claimed, while exploring the region now known as Suriname in South America in 1499
Curiously, Christopher Columbus did not mention any of these bright stars during any of his four voyages to the New World. Then again, most travelers to faraway places still ignore their opportunities to bring back reports of new sights in the sky.
Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium (opens in new tab). He writes about astronomy for Natural History magazine (opens in new tab), the Farmers' Almanac (opens in new tab) and other publications. Follow us on Twitter @Spacedotcom and on Facebook.