Term: celestial pole

The stars keep the same position relative to each other. For example, the stars forming the lip of the Big Dipper always point toward the tail star of the Little Dipper (which is the star Polaris). Thus we can consider the stars as attached to the dome of stars (celestial sphere). The fact that a star is not always in the same position in the sky tells us that the celestial sphere is not fixed overhead. It is moving. The motion of the celestial sphere in the sky is particularly simple. The fact that the motion is as simple as possible, was an attractive fact to the ancient Greek philosophers: it demonstrated design deserving an explanation.

Lets see if you can discover how the stars seem to move. Below find four pictures of the sky facing North, taken at 9 p.m., 12 midnight, 3 a.m., and 6 a.m. How are they related?