Page:Astronomy for Everybody.djvu/39

circle just touches the north horizon at its lowest point and, in our northern latitudes, extends to near the zenith at its highest point. The stars within this circle never set, but only seem to perform a daily course around the pole. For this reason this circle is called the circle of perpetual apparition.

The stars farther south rise and set, but perform less and less of their daily course above our horizon, till we reach the south point of it, where they barely show themselves.

Stars yet farther south never rise at all in our latitudes. They are contained within the circle of perpetual occultation, which surrounds and is centred on the south celestial pole, as the circle of perpetual apparition is centred on the north one.

Figure 2 shows the principal stars of the northern heavens within the circle of perpetual apparition for the Northern States. By holding it with the month on top we shall have a view of the constellations as they are seen about eight o'clock in the evening. It also shows how to find the pole star in the centre by the direction of the two outer stars or pointers in the Dipper, or Great Bear.

Now let us change our latitude and see what occurs. If we journey toward the equator, the direction of our horizon changes, and during our voyage we see the pole star constantly sinking lower and lower. As we approach the equator, it approaches the horizon, reaching it when we reach the equator. It is plain enough that the circle of perpetual apparition grows smaller until, at the equator, it ceases to exist, each pole being in our