Meet Crux, the constellation of the Southern Cross

Black star chart with Crux in light blue lines making a tee and dots with star labels.
Crux is the constellation of the Southern Cross. It lies deep in Southern Hemisphere skies. Image via EarthSky.

Crux the Southern Cross is one of the easiest constellations to spot in Southern Hemisphere skies. It consists of four relatively bright stars close to each other. 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 (around 26 degrees north latitude and farther south), can view the Southern Cross and its Jewel Box cluster on May evenings as it appears just above the southern horizon.

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How to find the Southern Cross

Crux lies between the constellations Centaurus the Centaur and Musca the Fly. You can locate it simply by looking for four bright stars close together. The stars are less than 5 degrees apart. Five degrees is about the width of your three middle fingers held at arm’s length. The compact size of Crux makes it the smallest of all the 88 constellations.

Crux looks like a cross but could also be considered kite-shaped. You can use the two stars that mark the long brace of the kite as pointer stars. Take the distance between these two stars and extend the line south 4 1/2 times its length to reach the south celestial pole. Unlike in the Northern Hemisphere, there is no bright star “pole star.”

Milky Way with stars forming a cross and neighboring constellations.
Crux the Southern Cross lies in front of the Milky Way with Centaurus and Musca nearby. Image via Stellarium.

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 320 light-years. It’s also the 12th brightest star in the sky.

Moving in a clockwise circle around the cross we come to the 2nd brightest star, Beta Crucis, sometimes called Becrux or Mimosa. Beta Crucis is magnitude 1.25 from a distance of 350 light-years.

Next, on the top of the cross, is Gamma Crucis, or Gacrux. Gacrux shines at magnitude 1.59 at a distance of 88 light-years. Finally, on the right side of the cross, is Delta Crucis. It shines at magnitude 2.79 from a distance of 360 light-years.

White chart with black dots showing cross shape at center.
The stars of Crux the Southern Cross. Image via Wikimedia Commons/ IAU/ Sky and Telescope.

The Jewel Box and other clusters in Crux

The Jewel Box is one of the most beautiful open clusters in the Southern Hemisphere. It lies just 1 degree from Beta Crucis. The Jewel Box, or NGC 4755, is bright at magnitude 4.2. Kappa Crucis, a magnitude 5.89 star, lies inside. You can see the Jewel Box 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?

Blue cluster of stars with one red one near center.
NGC 4755, or the Jewel Box, from ESO’s La Silla Observatory. Image via ESO.

The Coalsack Nebula

The easiest dark nebula to see in the sky is the Coalsack Nebula, found in the southeastern corner of Crux. The Coalsack is a dark, cloudy patch of dust and gas that obscures an entire swath of the Milky Way’s stars that lies behind it.

Dark nebulae: Black spot at center, surrounded by starfield and bright bluish star at top.
Meet the Coalsack, a huge cloud of gas and dust in space. The dust in this and other dark nebulae absorb and scatter the light of background stars. This creates a region of the sky that looks starless, but it’s really a place where new stars are forming. May is one of the best months to see the Coalsack in the constellation Crux in the Southern Hemisphere. This image is from the Wide Field Imager on the MPG/ESO 2.2-meter telescope. Image via ESO.
A man, seen from behind, looking outward over a city toward the labeled Southern Cross stars.
View at EarthSky Community Photos. | Prateek Pandey in Bhopal, India, caught the Southern Cross while at its highest point around midnight (its midnight culmination) on March 6, 2021. In April and May, the Southern Cross reaches its highest point in the sky earlier in the evening. Thank you, Prateek!

Bottom line: Crux, the constellation of the Southern Cross, is a hallmark of southern skies and contains the open cluster known as the Jewel Box.

May 12, 2024

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