Читать книгу The Friendly Stars - Martha Evans Martin - Страница 7

This constellation is so conspicuous and, hence, so easy to find, that it is known to most persons. It is one of the few constellations that really look like the things after which they are named. It lies in the northern heavens, and in our latitude is above the horizon all night, so that it can always be seen when the skies are clear. The two stars on the outer side of the bowl are called the "pointers," because a line drawn through them from bottom to top will point towards the North Star, and, if extended to about five times the distance between the two stars, will end, not exactly, but yet so nearly at Polaris that there will be no mistaking the star.

The North Star marks the centre, or pole, around which the celestial sphere revolves, and the pointers always hold the same relative situation to it no matter how the dipper is turned with relation to us. The North Star and the Dipper as they appear to an observer on the earth in our latitude at the different seasons of the year have the relative position shown in the illustration.

Inasmuch as all the stars seen in the northern hemisphere of the heavens revolve around the point marked by the North Star, their positions relative to one another are always the same. So if one bears this in mind, it will be just as easy to find them at one time in the year, or in the evening, as at another. The positions given in the diagram of the Dipper are as the stars composing it appear early in the evening at the seasons named. They make a circuit of the pole each twenty-four hours, so that if one watches all night he can see them in at least three of these positions each night in winter and in two of them during the short nights of summer. Into the other positions they come, of course, in the daytime.