Map II Key Map Orion

It is a pity that Orion is not circumpolar in England, as it is a magnificent

"signpost", as well as being a beautiful constellation in itself. It cannot be mistaken, as all its chief stars are brilliant, two of the first magnitude (Betelgeux and Rigel) and five of the second magnitude. Mintaka, Alnilam and Alnitak form the famous Belt. The periods of visibility of Orion in England can be judged from the following:

January 1st Rises 4 p.m., highest 10 p.m., sets 5 a.m. April 1st Rises in daylight, highest in daylight, sets 11 p.m.

July 1st Rises 4 a.m., highest in daylight, sets in daylight.

October 1st Rises 10 p.m., highest 5 a.m., sets in daylight.

It must be understood that these times are only very rough; Orion covers a considerable area, and takes some time to "rise". It is, however, clear that the constellation is best seen in winter and in early mornings in autumn.

The first-magnitude stars in the key map are easy to find if Orion can be seen. The three stars of the Belt (Mintaka, Alnilam, and Alnitak) point downwards to Sirius, which is the most brilliant star in the sky, though of course less bright than Venus, Jupiter, or Mars when well placed. Upwards, the Belt stars indicate Aldebaran in Taurus, a reddish first-magnitude star of about the same colour and brightness as Betelgeux.

Bellatrix and Betelgeux point more or less to Procyon, in Canis Major, which is not much fainter than Rigel; if this line is continued and curved slightly, it reaches a reddish second-magnitude star, Alphard, in Hydra, known as "the Solitary One" because it lies in a very barren region. The Twins, Castor and Pollux, can be found by a line from Rigel through Betelgeux; because they can also be found by using Ursa Major, this links the two key maps. Capella is indicated by a line from Saiph through Alnitak. Diphda in Cetus, the other star shown in the diagram, is less easy to find. It is only of magnitude 2, and is frequently visible when Orion is below the horizon.

Undoubtedly, a winter evening is the best time to start star recognition, because then both our "signposts", Orion and the Bear, can be seen. If a start is to be made in summer, we must do without Orion; but the Bear can by itself teach us the way about the heavens, and even though the stars seem at first to be arranged in a chaotic manner, it takes surprisingly little time to find one's way about.

Each of the following charts contains at least one key map object. Exact positions of telescopic objects, in right ascension and declination, are not given here, because an observer who possesses a telescope equipped with setting circles will in any case need a more detailed set of charts.


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