Story: Southern Cross
Page 3 – Stars and features of the cross
Many stars have names that indicate their brightness and location in a particular constellation. Astronomers call the Southern Cross the Crux and attach a letter of the Greek alphabet to the main stars in their order of brightness. The brightest star is at the bottom and, moving clockwise, the main stars are progressively dimmer.
The five stars
The brightest star is Alpha Crucis, also known as Acrux. It is the 14th brightest star in the sky and is really a triple star. When viewed through binoculars it appears as two blue-white stars. With a good telescope it is possible to discern that the brighter of the two is really another pair. They are located 321 light years from earth.
Beta Crucis, also known as Mimosa, forms the eastern tip of the upright cross. It is the second brightest star in the Southern Cross, and the 20th brightest star in the sky. Lying some 353 light years away, it is a blue-white giant star.
Gamma Crucis or Gacrux, at the top of the cross, is a distinct red-orange star, and stands out in contrast to the other, blue-white stars of the cross. It lies 88 light years from earth.
Delta Crucis is the faintest of the four stars making up the cross. Like Beta Crucis, it is a blue-white giant star. It lies some 364 light years from earth.
The faint fifth star, Epsilon Crucis, shows up as a dusty orange colour below and just to the left of Delta Crucis. It is not represented on the New Zealand flag, and is barely visible from light-polluted cities and suburbs. This star is an orange giant, located about 570 light years away.
Not starry eyed
Some early visitors to New Zealand were singularly unimpressed with the Southern Cross. Samuel Butler commented, ‘The southern cross is a very great delusion. It isn’t a cross. It is a kite, a kite upside down … with only three respectable stars and one very poor and very much out of place.’ 1
And an 1888 diarist wrote, ‘The Southern Cross … is a fraud, in as much as it is scarcely brighter than … its neighbours.’ 2
The Jewel Box
The Jewel Box is a cluster of stars beside Beta Crucis that can easily be seen through binoculars. It appears as a single, bright orange-red star set amongst eight blue and white stars. Through a telescope a group of about 50 blue-white stars can be seen. Astronomers classify this grouping as an open cluster – a loose collection of young stars formed at the same time – and list it in the New General Catalogue (a comprehensive list of deep-sky objects) as NGC 4755.
The Coal Sack
On dark moonless nights it is possible to make out an inky patch of sky just to the east of the Southern Cross, extending from the base of the cross toward Beta Crucis. Known as the Coal Sack, it is a dark nebula – a cloud of gas and dust dense enough to block out much of the light from the stars behind. It is estimated to be 600 light years away.