The Sky at Night

The night sky of the Mata Atlantica can be as impressive as it's wildlife, and as difficult to see. Of course it depends where you are. By the coast, the tropical heat and humidity tends to cause clouds at night, even after after a day of burning blue sky, whereas in the mountains the clean air and lack of ambient light can open up a vista of millions of stars, or valleys silvered by a brilliant moon.


But to a northern European, the sky is strangely unfamiliar. Orion is still there, but the other stars are rearranged in new patterns. How to identify them? One way is the excellent Stellarium program I have been playing with recently, a free download from www.stellarium.org. The beauty of it is that it's completely customisable. Open the menu by passing your cursor to the left hand side and under [location] input your coordinates and a 360 view of your night sky at that moment will appear (you can find your coordinates in various ways, but the easiest is probably to just put your town/village's name in wikipedia). Find the star you are interested in and click on it to give a name and some basic info. You can also set it up to show the planets automatically, arrange the stars in constellations, increase or decrease the level of background light pollution, and many more things.

So what did I see? The first thing I tried was to ID a constellation I've seen many times from my south facing balcony, but never found in any books. That was because it is in fact 2 constellations, one of which is the most famous of the southern hemisphere.

The Southern Cross is part of the culture of Brazil, on the flag and even the name of a major football team, Cruzeiro. Trace a line from Gacrux, the red one, across to Acrux and extend it about 4.5 times and you are looking, more or less, due South.

Of course the constellations are an optical illusion, Beta crux is 350 million light years away whilst Gacrux is "only" 88. The red colour of Gacrux comes from it being a red giant, a huge, but dying, star, the colour giving it the local name of Rubidia, or "ruby like". In contrast Delta crucis is known as "Palida" or the "pale one". The two pointers, Alpha and Beta Centauri, are technically part of the constellation Centaurus, but on a hazy night, or with lots of ambient light, they seem much more part of a tail to the "Y" of the Cross. Alpha Centauri is very bright, and for two reasons, it's actually three stars, two of which orbit around each other, and one is the closest star to Earth, at 4.2 light years away. Because it is so close Alpha Centauri is found in all sorts of science fiction, from Lost in Space, via Babylon 5 to Avatar, but of course these stars are also found in local mythology, showing local priorities. For the Xingu indians, the Southern Cross is the Curossow bird, whilst Alpha and Beta Centauri are a bird trap.