Northern hemisphere stars. Computer artwork of the brightest stars visible in the northern hemi- sphere, with lines of latitude (circles) and longitude (radii). The star clouds of the Milky Way appear as grey areas. The celestial north pole (which lies over Earth's north pole) is at centre, with the celestial equator forming the outermost circle. As the Earth spins during the night, an observer would see the stars apparently moving in circles around the north pole. The bright star near the north pole is Polaris, the Pole Star; it is a valuable aid to navigation because it hardly moves at all. (See image R800/154 for the southern hemisphere).