If we see at the sky for some time at night, then we will observe some stars forming groups with shapes. So, the shape formed by the group of stars is called a constellation diagram. The shapes of constellations resemble objects familiar to those people. Each constellation is signified by an animal, a human being, or some other objects it appears to resemble. All the constellations seem to move in the sky from east to west. This is due to the rotation of the earth on its axis from west to east.