Over the course of the night, stars move across the sky from east to west as a consequence of Earth's rotation on its axis. The stars appear to move in circular paths around a celestial pole, or either of two points on the celestial sphere where the extensions of Earth's axis would intersect. In the Northern Hemisphere, the celestial pole is coincidentally marked by the relatively bright star alpha Ursa Minoris, also known as Polaris. Simple geometry shows that the altitude angle of the pole star above the northern horizon is equivalent to the latitude of the observer on Earth.

To an observer in the Northern Hemisphere, stars that are always above the northern horizon are known as circumpolar stars; an observer in the Southern Hemisphere would see circumpolar stars around the south celestial pole. Stars that are further to the south and that rise and set sometime during the night are called equatorial stars. Equatorial stars rise in the east, move diagonally into the southern sky, achieving their highest position above the horizon on the meridian (the great circle that extends from due north on the horizon, through the zenith, to due south on the horizon). From the meridian, these stars move westward until they set below the western horizon.