Map I Key Map Ursa Major The Great Bear

Almost everyone must know the Great Bear. Its seven stars are a familiar feature of the night sky, and it is of course so far north that it never sets in the latitude of England. The proper names of the seven are frequently used: in addition, Merak and Dubhe are popularly known as the "Pointers".

The first step after having identified the Bear is to find the Pole Star. Imagine a line drawn from Merak through Dubhe, and extended; it will reach a second-magnitude star rather "out on its own", and this is Polaris. The Little Bear, Ursa Minor, can then be picked out, bending back towards the Great Bear itself. The stars are much fainter, but one of them, the rather reddish Kocab, is of magnitude 2.

Now imagine a line from Alioth, in the Great Bear, through Polaris. Extended for an equal distance on the far side of Polaris, it will reach five brightish stars (magnitudes 2 to 3) arranged in a rough W. This is Cassiopeia, which, like the Bears, never sets in England.

A line from Megrez through Dubhe will come eventually to Capella, which is one of the brightest stars in the entire sky. It is circumpolar in England, but at it lowest, as during summer evenings, it almost reaches the horizon. In winter evenings it is high up and may indeed pass overhead. If you see a really bright star straight above you, it can only be Capella or Vega; Capella is yellowish and may be recognized by the small triangle of stars close by it, whereas Vega is decidedly blue. Vega can be found by means of a line beginning at Phad, passing between Megrez and Alioth, and extended for some distances across the sky.

The remaining stars shown in Map I are not circumpolar. The Twins, Castor and Pollux, may be found by means of a line from Megrez through Merak; they are at least at their best in winter. Regulus and the other stars of the Lion, found by a line from Megrez through Phad, seem to follow the Twins in the sky; the curved arrangement of stars rather like a reversed question mark, of which Regulus is the brightest, is known as the "Sickle of Leo", and is easy to recognize. Even easier is Arcturus, about as bright as Capella and Vega. This is found by means of a line from Mizar through Alkaid, and curved rather downwards; if the curve is continued through Arcturus it comes to another first-magnitude star, Spica, in Virgo.

Arcturus and Spica are prominent features of the spring and summer skies of England.

It may be added that Arcturus shines with a distinctly orange light, so that it cannot be confused with Capella or Vega.

224 The Amateur Astronomer

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