The Southern Hemisphere sky is adorned with many interesting constellations that most northern viewers never see. One of these is Crux, or the Southern Cross. It's the smallest constellation in the sky and yet boasts one of the most elegant and distinctive patterns of stars--a crucifix. One of its star clusters is so lovely it's named the Jewel Box.
In ancient times in the low northern latitudes where the constellation could be seen, these stars were considered part of Centaurus, and today Centaurus surrounds Crux on three sides. Several hundred years ago, Crux helped guide early European explorers of the Southern Hemisphere, for the upright of the cross points to the south celestial pole. (Unlike the north celestial pole, which is marked by the North Star, Polaris, the south celestial pole is unmarked by any bright star.)
On a clear night the Milky Way, which runs through Crux, appears as a cloudy area, an effect produced by the blending of the light of myriad stars too faint and too far away to be seen individually. Within the boundaries of Crux, on the eastern side near the bottom of the cross, is a large dark area where the starlight is obscured by a huge cloud of dust and gas. This region, which looks like a hole in the Milky Way, is the Coal Sack Nebula, the most famous dark nebula in the sky. Its light-absorbing dust is like a cosmic curtain, blocking out any stars behind it.
Planets of the Week
Mars is above the western horizon in the evening hours, setting at about 10:00 p.m. High in the sky at sunset, Saturn shines against the glittering backdrop of the constellation Taurus. Jupiter appears eastward of Saturn it in the constellation Gemini and is the brightest object in the sky these nights, after the moon.
At 9:00 p.m. on January evenings the last of the late-summer and fall constellations are just about to set. Deneb, the bright alpha star in the constellation Cygnus, is just above the northwestern horizon. The Great Square of Pegasus is almost due west, and the constellations Cepheus, Cassiopeia, Perseus, and Andromeda, somewhat higher, are still visible. Ursa Minor, also known as the Little Bear or the Little Dipper, hangs almost straight down from Polaris, the North Star.
Leo, the Lion, and its bright alpha star Regulus are just rising in the east-northeast. Between Leo and Gemini lies the faint zodiacal constellation Cancer, the Crab. To the north is Ursa Major, the Great Bear. The Big Dipper, a part of that large constellation, stands upright on its handle.
The southeastern quadrant of the sky holds Orion, the Hunter, one of the brightest and most easily recognized constellations. Orion also serves as a pointer to several other constellations. The three equally bright, evenly spaced stars of Orion's belt point roughly toward Aldebaran, the alpha star in Taurus, to Orion's west, and toward Sirius, the alpha star in Canis Major, to the southeast. Sirius, also called the Dog Star, is the brightest star in the sky. Above Orion's belt are the stars of its shoulders: the brighter, eastern star of the two is the red star Betelgeuse; the other is called Bellatrix. Below the belt are two stars marking Orion's knees: the brighter, western one is the bluish-white star Rigel; the other is Saiph.
A line drawn from Rigel through Orion's belt to Betelgeuse and then extended northward points just north of Gemini, the Twins, and that constellation's two brightest stars, Castor and Pollux. Between Gemini and Canis Major lies the bright star Procyon, the alpha star in Canis Minor, the Little Dog.
There are few bright stars in the southwestern portion of the sky. The dim but large constellations of Pisces (the Fish), Cetus (the Sea Monster), and Eridanus (the River) span most of the western and southwestern sky. Near the meridian high in the south is Taurus, the Bull. The bright orange star Aldebaran marks its eye, and the V-shaped star cluster the Hyades marks its face. High in the southwest is the lovely star cluster known as the Pleiades, or the Seven Sisters. Almost overhead is Capella, the bright star in Auriga, the Charioteer.