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.

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