Sunday, 17 April 2011

Hunter in the Night Sky

Look to the south and you will see the Southern Cross and Alpha Centauri, but look away from there from November to February and the most conspicuous constellation you will see is Orion, possibly the best known constellation on the planet! Conspicuous and visible from all over the Earth, everyone, from the ancient Egyptians to the Aztecs to the Aboriginal Australians has Orion in their mythology

As everyone knows, Orion is basically four stars, the arms and legs of the Hunter, surrounding his "belt".

A screenshot from Stellarium, 8pm 15th April

The bright red star is Betelgeuse, the strange name coming from the Arabic al-jauza (the name of the constellation) and abet, meaning centre or armpit, so Betelgeuse means "Orion's armpit". Be that as it may, Betelgeuse is huge, if it were placed in the centre of our solar system its surface would extend out to Jupiter. Huge, but not long for this universe being a decaying super giant - when it finally explodes it should be visible from Earth during daylight.

Opposite Betelgeuse is the blue star Rigel, the brightest star in the constellation. Again named from the Arabic, Rigel is a shortened form of Riǧl Ǧawza al-Yusra, which means basically "Orion's left foot". Actually Rigel is two stars, a binary system, which is why it's so bright.

The Belt, three stars together in a straight line, has many names. In Latin America it's known as the Three Marys, a reference to the three biblical Marys who came to the sepulchre of Jesus in the Gospels and were companions of a 4th Mary, the mother of Jesus. Mary Magdalene, Mary of Cleopas and Mary, mother of James. Of course the three stars of the belt are nowhere near each other, they just look that way from here. The star in the middle, Alnilam, is actually 375,000 brighter than the sun, but perhaps fortunately, is 1340 light years away.

The other two stars are Saiph and Bellatrix. Saiph again has an Arabic name, a corruption of saif al jabbar or "Sword of the Giant". It looks faint to us but that's because us humans cannot see UV light, in fact it's as bright as Rigel, but much hotter and most of it's light is ultra violet.

And lastly Bellatrix, the "Amazon star". Bellatrix is "Female Warrior" in Latin, and technically the star is an "eruptive variable" - thus this is perhaps a fitting name for the extremely dangerous, though barking mad, adversary of Harry Potter.

Tuesday, 12 April 2011

A New Rat

The world always needs more rats (doesn´t it?) and so you will pleased to know that a new one has been discovered! Drymoreomys albimaculatus is orange, hairy and lives in trees.

Actually, Drymoreomys albimaculatus are very, very, rare, even one of the authors of the paper describing them had never seen a live one. They live on the eastern slopes of the Serra do Mar, in the coastal Brazilian Atlantic rainforest from São Paulo down to Santa Catarina, at altitudes of 650 to 1200m. Which means cold damp forest with winter temperatures down to below 0 C, which is probably why they have unusually long thick fur. Although all the ones that have been caught were on the ground, they probably climb trees as they have long prehensile tails and special pads on the palms of their paws for climbing.

Drymoreomys means forest mountain rat, and albimaculatus refers to the white spots they have in their orange pelt. And that's about it. Their life cycle, predators, place in the ecosystem is a mystery. Goodness knows what they eat, probably everything, rats aren´t usually fussy.

Sunday, 10 April 2011

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 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.