Written: 5th Jun 2004 | Last Updated: 6th Jun 2004
For those of us who call Australia home, there is a heavenly constellation most dear to our hearts. It is Crux, Crux Australis or simply The Southern Cross.
When we are home, it reminds us of who and what we are. When we are away, we long for it – that sparkling reminder of life in the antipodes. Its stars are treasures sewn into our flag - symbolising national character, history, bravery, accomplishment and hope.
The Southern Cross was once part of the constellation Centaurus, but astronomers and navigators of the 16th century considered the beautiful, latin cross a fine symbol of their faith and therefore worthy of a separate constellation. The general belief is that it was mathematically dissected from Centaurus and named Crux Australis by French astronomer Augustin Royer in the 17th century. But the Crux was also distinctly mentioned in letters written by Andrea Corsali in 1515, when he made a beautiful, woodcut engraving of it.
While Crux Australis may be the smallest constellation in the sky, it has the highest concentration of bright stars of any. Alpha Crucis (a binary, i.e. two blue-white stars orbiting one another, but seen as one), Beta Crucis (a blue-white giant known as Mimosa, and nearly five times the size of our sun) and Gamma Crucis (which forms the top of the cross) are the brightest stars, while Delta Crucis hides ever so slightly in the light-wash of this dense part of the Milky Way. The fifth main star, Epsilon Crucis, is represented by the smallest star on the Australian flag.
The Pointers, Alpha and Beta Centauri - which famously point in the direction of Gamma Crucis (the top of the cross) - are astronomical constants which helped ancient sailors and explorers to find Crux Australis. The constellation’s long axis points towards the south celestial pole, thus making it highly suitable for both navigational and time measurement purposes.
Alpha Centauri (a triple star and the third brightest star in the sky) and Beta Centauri are easily picked out on a clear night. There is also a large, false cross in the southern sky known as Carina, which may have led many travellers astray! Its pointers aim towards the bottom star while the true Southern Cross pointers always aim towards the top.
The Crux Australis stars are figured to be somewhere between 200 and 600 light years from Earth. The Jewel Box, or the Kappa Crucis Star Cluster, is a brilliant open cluster of one hundred stars located just near Beta Crucis. It is about 7,600 light years away. Its colourful jewels – red, blue, yellow and white stars - are just visible to the naked eye.
A large, dark nebula known as The Coal Sack, is another feature of this part of the galaxy – it is located just to the south of The Jewel Box, about 500 light years away. It is made up of massive clouds of galactic gas and dust, and is also visible to the naked eye.
It is believed the four main stars of The Southern Cross could be seen just on the horizon from the Near East and Jerusalem during Biblical times. But it has moved so deeply to the south that it can no longer be seen above latitudes of 27 degrees north. The constellation has often been considered to have mystic and religious significance – some suggest symbolically that it left the Northern Hemisphere after the crucifixion of Christ.
The constellation features strongly in Australian Aboriginal dreamtime stories as well as Maori and Pacific Island legends. The charisma of Crux affected all the early Pacific explorers who felt guided and protected by the stellar cross. Even Charles Darwin ranked it the finest of the southern heavenly spectacles during his voyages in The Beagle.
Next time you look up at a clear, night sky from somewhere in the Southern Hemisphere – particularly from anywhere in Australia – search for The Pointers and Crux Australis. They will affect you, dazzle you, romance and possibly guide you just as they have others for millennia.