The stars appear to move from east to west across the night sky because as Earth rotates, the sky is observed as rotating, according to Astronomy Education at the University of Nebraska–Lincoln. Observers on Earth, in both the northern and southern hemispheres, see objects in the sky move counter-clockwise.
The stars maintain their formations as they move across the night sky, explains Daniel V. Schroeder of the Weber State University Physics Department. As such, the perceived distance between individual stars remains constant. Although a specific pattern of stars may face varied directions at different times, it never grows larger or smaller or takes a different shape. Such a pattern is perceived by an observer on earth as a constellation.
The revolution of Earth around the sun causes stars to seem to shift positions in the night sky, according to NASA’s Imagine the Universe. Thus, as the Earth takes one year to orbit the sun, an observer may see different patterns of stars in the sky depending on the time. For instance, constellations seen at night during winter differ from those appearing in the summer. However, planets move around the sun along a certain path, as observed from Earth, the sun and moon.