Page:The Music of the Spheres.djvu/23

 groups which do this for an observer in the north temperate latitudes. If watched throughout the night any one of these star groups may be seen to complete half of its circle around the North Star, although the other half of the journey would be invisible on account of the daylight.

Although the circumpolar stars may be seen to complete their pathways above the horizon, the pathways of all the other stars are completed on the other side of the earth,—the greater the distance from the North Star, the larger their arcs above the horizon, until the distance of 90 degrees is reached. This greatest curve is shown by the stars which rise almost directly in the east. The stars which rise south of east have only a small portion of their pathways visible.

It would seem that since the stars move as a complete unit, the aspect of the star dome would appear the same at the same hour of the night throughout the year. But this is known not to be the case for in consequence of the earth's motion around the sun, or the apparent advance of the sun among the stars, the same position of the stars re-occurs four minutes earlier each day, and the star groups appear a little farther west at a given hour each evening. They appear at the same time only after the lapse of a year. This is the reason that the dates and hours for the appearance of the different stars are given in the star maps. Since four minutes a day total up to two hours a month, a star seen to rise at ten o'clock in one month will be seen to rise at eight o'clock the next month, and at six o'clock the following month, and so on through the daylight at the rate of two hours a month, until it has again worked back to a place in the darkness of the evening sky.

The number of the stars is beyond determination, but those visible to the unaided eye amount to only a few thousands.