Observing the Constellation Crux
Stars and Deep-Sky Objects in the Southern Cross
Crux, the Southern Cross, is one of the easiest constellations to spot in Southern Hemisphere skies. It consists of four relatively bright stars in close quarters. It stays above the horizon year round for observers in the Southern Hemisphere, but it can be seen by those in the southern reaches of the Northern Hemisphere for a short time each year. For example, observers in southerly latitudes around Miami, Florida, can view the Southern Cross and its Jewel Box on May and June evenings as it appears just above the southern horizon.
How To Find the Southern Cross
Crux is located between the constellations Centaurus and Musca. It is easy to locate simply by looking for four bright stars all less than five degrees apart. Five degrees is about the width of your three middle fingers held at arm's length. Crux is the smallest of all 88 constellations.
Crux not only looks like a cross but can be considered kite shaped. The two stars that mark the long brace of the kite are often used as pointer stars. Take the distance between these two stars and extend the line south four and a half times its length to reach the south celestial pole. Unlike in the Northern Hemisphere, there is no bright star "pole star".
Stars of Crux
The brightest star of the Southern Cross is Alpha Crucis, or Acrux. It is the bottom star of the cross and shines at magnitude 0.77 from a distance of 321 light-years. Moving in a clockwise circle around the cross we come to the next brightest star, Beta Crucis, sometimes called Becrux or Mimosa. Beta Crucis is magnitude 1.25 from a distance of 353 light-years. Next up, on the top of the cross, is Gamma Crucis, or Gacrux. Gacrux shines at magnitude 1.59 at a distance of 88 light-years. The next brightest star is Delta Crucis, shining at magnitude 2.79 from a distance of 364 light-years. Between Delta Crucis and Acrux is a dim star that lies along the line of the kite-shape. This is Epsilon Crucis, shining at magnitude 3.59 from a distance of 228 light-years.
The Jewel Box and Other Clusters in the Southern Cross
The Jewel Box is one of the best known clusters in the Southern Hemisphere. It lies just one degree from Beta Crucis. The Jewel Box, or NGC 4755, is bright at magnitude 4.2. Kappa Crucis, a magnitude 5.89 star, is found inside. The Jewel Box can be seen without optical aid, but a pair of binoculars or a telescope will bring more of the stars into focus. Can you see color differences between these glittering gems?
Six other star clusters between 6th and 9th magnitude lie within this small patch of sky. The clusters, in order from brightest to dimmest, are
- NGC 4609 at magnitude 6.9
- NGC 4103 at magnitude 7.0
- NGC 4349 at magnitude 7.4
- NGC 4439 at magnitude 8.4
- NGC 4337 at magnitude 8.9
- NGC 4052 at magnitude 9.0
