Sunday, July 27, 2014
Who discovered the Southern Cross?
I recently received an email asking me, amongst other things, who discovered the Southern Cross.
The question of who "discovered" Crux, the Southern Cross, is complex. The Southern Cross would have been familiar to the Ancient humans who lived in Africa, before they expanded out of Africa and in to the rest of the World. Some modern South African groups see the Southern Cross as part of a group of giraffes.
By 40,000 years ago humans had colonised Australia, where the Southern Cross takes pride of place in the sky. The Karuna people of the Adelaide Pains, where I live now, saw the Southern Cross as the footprint of the Wedge Tailed Eagle, Wilto. The Boorong Peoples of the Western Victorian Plains, where my spouses family live, see the Southern Cross as a ring tailed possum. Other indigenous groups see it as part of a larger constellation of an eagle, or as a stingray.
I've made a cross-eyed stereo image of Crux, the Southern Cross. Stare at the picture and cross your eyes until the x of Crux aligns, and the stereo version will pop out at you (you can click on the image to embiggen and get a higher definition view).
But the tilt of the Earth's axis slowly changes due to precession. Over a thousand years ago the Southern Cross was lost from the northern skies as the Earth's tilt increased. It was first sighted by Europeans when Portuguese and Spanish explorers entered the Southern seas. Amerigo Vespucci mapped the stars of the constellation during his expedition to South America in 1501, depicting Crux as an almond! It then appeared as "Crux" on star charts from Petrus Plancius and Jodocus Hondius in 1598 and 1600.
The are 5 primary stars in Crux, in order of brightness Alpha Crucis (Acrux), Beta Crucis (Mimosa), Gamma Crucis (Gacrux), Delta Crucis and Epsilon Crucis. The four brightest form the obvious cross shape of the constellation.
Printable black and white chart of the Soutern Cross, suitable for binoculars (click to embiggen and print)
Alpha Crucis, the brightest star of the Southern Cross is the 12th brightest star in the sky. In a small telescope it is an easily resolvable double star. This blue-white giant star is 320 light years away from us.
The Jewel Box is one of my favourite open clusters.
Beta Crucis is another blue-white giant star, 353 light years away from us, in a pair of binoculars or small telescope you can see the beautiful Jewel Box cluster (NGC 4775). Between Alpha and Beta Cruscis lies the edge of the dark nebula, the Coal Sack (Yurakawe to the Karuna people).
Gamma Crucis is a red giant, 88 light years away and Delta Crucis is also a red giant, although 360 light years away.
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