Space

The barbecue stars

In the dusk of a summer's evening the smoke from barbecues and campfires rises into a darkening sky full of brilliant stars. Centre stage is the Pot, with a line of three stars forming the bottom of a southern hemisphere saucepan or dipper. These stars run across the celestial equator, so they are also visible, upside down, in the northern hemisphere. There they are known as the Belt and Sword of Orion the Hunter, a giant figure of a man holding a raised club and surrounded by a group of animals. Adolf Hitler is said to have wanted to rename this constellation after himself. The stars in the handle and base of the Pot are young, only a few million years old, and they lie in a part of the sky where even younger stars are still forming. Binoculars will show up one of these star nurseries in the middle of the handle of the Pot. Here there is a beautiful nebula, a cloud of dust and gas lit up by the young hot stars which have formed within it. Some are not even visibly shining yet, but watch this space—in years to come they will blaze out through the dust clouds. A simple way to measure distances in the sky is with a hands pan. Stretch your arm as far as you can, spread your fingers wide, and the distance from thumbtip to little fingertip is about 20 degrees on the sky. Using this measure, one handspan from the right hand star in the base of the Pot reaches Sirius, the brightest star in the whole sky. Sirius means 'scorching', so named because Mediterranean people saw this star approach the sun in the hottest part of the year and assumed that it was causing the extra heat. It is also called the Dog Star, because it 'dogs' Orion the Hunter, and from this association comes the name 'dog days', for the sultry days of late summer. Sirius is bright partly because of its closeness to the Earth (about eight and a half light years) but also because it really is a giant star, nearly 23 times as luminous as our sun. On the other side of the Pot, a hands pan from the left hand star in the base takes you to Aldebaran, an old red star in the eye of Taurus the Bull, with the V-shaped Hyades cluster forming the Bull's nose. Further left again is a little cluster known variously as Matariki, the Pleiades or the Seven Sisters. Six brighter stars are easily visible to the naked eye, although a telescope shows more than 200. There is some argument as to whether one of an original seven bright sisters has faded, or whether the cluster was given its name only because seven was considered a magical number. The sisters feature in more legends and literature than any other constellation. Often these stories mention rebirth or renewal and are linked with the beginning of the northern agricultural year, the beginning of the monsoon in Asia and with the corn harvest in western European traditions. Maori elders watched in the dawn for the first appearance of Matariki from behind the sun on a date near enough to the shortest day, and used it to set the beginning of a new year. South African tribesmen called the Pleiades the 'hoeing stars'—a sign that it was time to begin another farming cycle. Many constellations are only chance alignments of stars which are really at different distances, but the Hyades, Pleiades and Pot are all real families. The Hyades are the closest, at about 150 light years. They are a crowd of about 200 stars all travelling together in the same direction, and probably formed from the same dust cloud. The odd man out among them is Aldebaran itself, which is an unrelated star in the foreground. The Pleiades are more than twice as far away. They are one of the youngest clusters, only formed about 50 million years ago, and a telescope shows them still cocooned in the smoky nebula from which they formed. The stars of the Pot are much further away—so distant that the light which reaches us from them this evening began its journey more than a thousand years ago. Among the planets, Jupiter is unmistakeably bright through the summer. Steady your binoculars against a doorpost and see if you can find Jupiter's moons as minute points of light which change position from one night to the next. Venus is still a morning star, low in the dawn twilight.

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