Our planet Earth is a spherical globe which revolves around its own axis, an imaginary line that runs through the center of the Earth from the north pole to the south pole. If it were not for the stars beyond Earth's atmosphere, it would be difficult to prove.
A SHIFTING HORIZON As Earth rotates from west to east, our perception is that the stars, the Sun, and all other heavenly objects move around us in the opposite direction from east to west. The apparent motion of the stars in the sky, will depend on where you are.
At the North Pole, 90° N For this observer, the celestial north pole, marked by the star Polaris, corresponds with the zenith, the point in the sky directly overhead. From this position on Earth, the celestial equator is parallel with the horizon, and because the stars move along a parallel to this horizon, only the stars in the northern half of the celestial sphere are ever visible.
At the Equator, 0° From this latitude, an observer can see all the stars of the sky. The celestial equator rises up in an imaginary vertical line from the horizon and runs through the zenith. The north and south celestial poles lie exactly on the horizon. The stars in the east rise straight up and sink straight down again below the horizon in the west.
At 40° S Latitude For all locations lying between these latitudes, there is a part of the sky that always remains invisible, that which surrounds the celestial pole of the opposite hemisphere. The area of the sky close to the visible pole remains in view all the time. Stars here never set, but seem to circle around the celestial pole. These are called circumpolar stars, and the closer you are to the pole, the more circumpolar stars there are.
