The time of the crow

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With the advance of autumn the constellation Corvus, the crow, soars almost directly overhead.

Of all the 88 constella­tions, Corvus is one of the few in which the pattern of stars is recognisably related to the named object, in this case a crow flying east to west. Appropriately, the bird of ill omen brings the winter constellations in its train.

Looking south, Crux, the Southern Cross, stands upright with the two bright Pointers immediately east of it.

Alpha Centauri, the brighter and more easterly of the Pointers, is the third-brightest star in the sky and is actually a system of three stars. The two brightest, or­biting their common centre of mass, form the star seen by the naked eye.

Around this pair orbits the faint dwarf, Proxima Centauri, which at 4.3 light years is the closest star to the sun.

Due north from Corvus the eye sweeps through Virgo and, immediately below it, Coma Berenices, the hair of Berenice. These two constellations are no­table for the large number of bright galaxies in their area as well as the great Coma star cluster which is well seen with the aid of binoculars.

The Coma/Virgo cluster of galaxies has over 3000 members, each a star system comparable to our Milky Way galaxy. About 100 of these are visible in 150mm to 200mm diameter telescopes on a clear, moonless night when well away from urban sky glare.

To the eye, even when aided by a large telescope, the majority of even bright galaxies appear as little more than patches of ghostly light. Long expo­sure photographs reveal them to be huge collections of stars counted in tens and even hundreds of millions, forming galaxies of various types from the egg or ball-shaped ellipticals to the great spiral systems like our own.

Although this group of galaxies is the nearest such association to us it is nevertheless estimated to be rather more than 40 million light years away. Thus the light we perceive today set out about the time when the early mammals were beginning to dominate the land, and not long after the end of the Carboniferous, which saw the final extinction of the dinosaurs.

Fifteen degrees ENE of Corvus is the bright star Spica, Alpha Viginis, another double star but in this case with the primary much brighter than the secondary.

Arcturus, Alpha Boot, is twenty degrees NNE of Corvus and is the brightest star north of the equator. On cold nights, when the stars are twinkling, it flashes white through to orange, forming a spectacu­lar celestial jewel.

This huge, old star is in fact only a temporary neighbour. It is passing almost at right angles through the equatorial plane of the galaxy and will in a few thousand years be growing fainter as it races away from us out of the Milky Way disk.

North-west of Corvus is Leo, the constellation figuring a crouching lion which features in both eastern and western mythology and astrology from the earliest times.

The head and chest form a distinctive sickle shape and its rising just before sunrise heralds the begin­ning of spring.

Leo was of particular importance to the ancient Egyptians because it heralded the annual flood­ing of the Nile.

To Southern Hemi­sphere viewers the head and chest of the lion lie in the sky like a sacking hook — a more familiar shape here, though less romantic.

Regulus, the Little King or Alpha Leonis, is the very bright star marking the lion’s chest. It is known to the Arabs as Al Kalb al Asad, the heart of the royal lion. This large, very hot, blue-white star is another example of a multiple system, for it has a distant, faint companion which is itself a double star.

In fact, few stars form in isolation; most are mem­bers of multiple systems. The great clouds of gas and dust which are the raw material from which new stars arise are so large and complex that as they contract and heat up multiple centres of fusion arise. These in turn may initiate still further pro­tostellar activity and more stars.