The Southern Cross

The Southern Cross, known to astronomers as Crux, is the most famous constellation in the southern sky and the smallest of all 88 official constellations. Its four bright stars form a clear cross shape that sits in a particularly rich part of the Milky Way. The Southern Cross is so important to the southern hemisphere that it appears on the flags of Australia, New Zealand, Papua New Guinea, Samoa and Brazil.

  • Best seen fromSouthern hemisphereVisible everywhere south of approx. 20 degrees N
  • Best viewing timeAutumn evenings(Southern hemisphere)
  • Size rank88th (smallest)Just 0.16% of the entire sky
  • Brightest starAcruxBlue giant, 320 light years away
  • Famous dark nebulaThe CoalsackDark cloud of dust next to the Cross
  • On the flag of5 countriesAustralia, NZ, PNG, Samoa, Brazil

The four (and a half) stars of the Cross

The Southern Cross has four main stars in a clear cross or kite shape, with a fifth fainter star sometimes included to make a more accurate diamond.

  • Acrux (Alpha Crucis): the brightest, at the foot of the cross. Acrux is itself a system of at least 6 stars.
  • Mimosa (Beta Crucis): on the left arm of the cross. Mimosa is a hot blue giant about 280 light years away.
  • Gacrux (Gamma Crucis): the red star at the top of the cross. It is a red giant only 89 light years away, much closer than the others.
  • Imai (Delta Crucis): on the right arm of the cross.
  • Ginan (Epsilon Crucis): the smaller fifth star, often shown inside the kite shape on the Australian flag.

Even with just the four brightest stars, the Cross is a beautiful sight. From a dark sky in the southern Milky Way, the contrast of the bright blue stars next to the deep dark patch of the Coalsack nebula is unforgettable.

How to find the Southern Cross

From everywhere south of approximately 20 degrees north latitude, the Southern Cross is easy to spot. Look towards the south on a clear night. You should see four bright stars in a clear cross shape, sitting in front of a bright patch of the Milky Way.

You can confirm you have got the right thing by checking two bright stars to the left of the Cross. Those are the Pointers: Alpha Centauri and Beta Centauri, part of the larger constellation Centaurus. A line drawn from Beta through Alpha and continued in that direction takes you straight to the long axis of the Cross, which is itself useful for finding south.

Using the Cross to find south

Unlike the northern hemisphere, the southern hemisphere has no convenient "South Star" sitting close to the south celestial pole. But you can still find south using the Cross.

  • Imagine a line drawn down the long axis of the Cross (from Gacrux at the top, through Acrux at the bottom).
  • Extend this line for about 4.5 times the length of the Cross itself.
  • The point you arrive at is the south celestial pole.
  • Drop straight down to the horizon from there and you are facing south.

Sailors, navigators and bush travellers in the southern hemisphere have used this trick for at least 500 years.

Fact Right next to the Southern Cross is one of the largest and most famous dark nebulae in the sky, called the Coalsack Nebula. It looks like a deep, jet-black hole in the bright band of the Milky Way. The Coalsack is not actually empty: it is a cloud of dark dust about 600 light years away that blocks the light from the stars behind it. Australian Aboriginal peoples have stories about the Coalsack going back thousands of years.

On the flags of the southern hemisphere

The Southern Cross is such a powerful symbol of the southern hemisphere that it appears on the national flags of five countries:

  • Australia: five white stars representing all 5 stars of the Cross, plus a larger Commonwealth Star.
  • New Zealand: four red stars with white borders representing the four brightest stars only.
  • Papua New Guinea: five small white stars on a red background.
  • Samoa: five white stars, with the four largest forming the Cross.
  • Brazil: 27 stars in total, including the Southern Cross arranged exactly as it appeared in the night sky of Rio de Janeiro at 8:30 am on 15 November 1889, the day Brazil became a republic.
Did you know? The Southern Cross is sometimes confused with the "False Cross", another cross-shaped pattern of four bright stars in the nearby constellations Carina and Vela. The False Cross is bigger and dimmer, and points to a different patch of sky entirely. Experienced southern stargazers learn to spot the difference by looking for the two bright Pointer Stars in Centaurus, which always sit next to the real Southern Cross.
Deeper dive: why ancient Greeks knew the Southern Cross but Europeans forgot it

The Southern Cross is too far south to be easily visible from most of Europe today. But over 2,000 years ago, it WAS visible from the Mediterranean. Ancient Greek astronomers, including Ptolemy, recorded its stars and treated them as part of the larger constellation Centaurus.

Then a slow process called precession (the same long-term wobble of Earth's axis that changes the pole star) gradually shifted the Cross out of the European sky. By the Middle Ages, the Cross had dropped below the horizon for most of Europe and was forgotten.

The Cross was rediscovered by European sailors during the Age of Exploration in the 1500s, when ships first sailed deep into the southern hemisphere. Portuguese and Italian explorers, including Amerigo Vespucci, wrote excited descriptions of the bright new cross-shaped pattern in the southern sky. The French astronomer Augustin Royer formally split it off from Centaurus and made it the new constellation Crux in 1679. Today it is so iconic that the much larger Centaurus seems almost like a frame around it.

For northern-sky equivalents, see Ursa Major and Ursa Minor, or browse what is a constellation.