Crux - The Southern Cross

Crux, known as the Southern Cross, is perhaps the most famous southern constellation. It is also the smallest constellation in the sky, and covers only 68 square degrees. The Southern Cross points to the South Celestial Pole, in the same way as the pointer stars of the Big Dipper point to the North Celestial Pole.

History and Mythology

Crux was considered part of the Centaur's feet in ancient times. It took on its own identity in the 15th and 16th centuries, when Christian nations of Europe explored the southern continents. Hundreds of years ago, Crux helped guide early European mariners into the Southern Hemisphere. The long axis of the cross points to the South Celestial Pole, thus indicating the direction toward due south. This constellation was formalized in the 17th century.

Notable Stars

Acrux is a double star, blue-white in color, with components of magnitude 1.4 and 1.9, separated by 4.4 arcseconds. It is the 14th brightest star in the sky. It is located 320 light years from our solar system, and composed of two hot blue-white stars with luminosities 25,000 and 16,000 times the Sun's.

Beta Crucis is a blue-white star of magnitude 1.3, and is the 20th brightest star in the sky. It is also a very hot star, with a luminosity of 34,000 Suns, located 350 light years away.

Gamma Crucis is the third-brightest star in Crux, a red giant of magnitude 1.6. It is 88 light years away, has a luminosity of 1,500 Suns, and has a white, 6th-magnitude companion 25 arcminutes away, which appears to be a physically unrelated star four times more distant.

Clusters, Nebulae, and Galaxies

Crux lies along the southern Milky Way. It is rich in star clusters, and includes the Coal Sack dust cloud. NGC 4755 is called the Jewel Box cluster. It contains about 60 stars ranging in magnitude from 6 to 10. The Jewel Box is one of the brightest and youngest clusters known. The stars are mostly supergiants and probably only a few million years old. In a telescope, the Jewel Box is the finest open cluster in the southern skies.

The Jewel Box is near the northern edge of the Coal Sack, the most famous dark nebula in the sky. The Coal Sack appears as a hole in the Milky Way, where the light from distant stars is obscured. It forms a nearly starless region near the bottom of the cross.

NGC 4052 is an open cluster with stars of 8th magnitude. The open cluster NGC 4103 is made up of some 25 7th magnitude stars. NGC 4349 is a large, star-colored cluster positioned halfway between Acrux and Epsilon. These clusters, as well as the Jewel Box, can be easily seen with binoculars.