Constellations refer to a group of stars that form a certain shape in the sky.  Just like any other star in the sky, many people perceive them as moving objects. At one point during a clear night, one may notice a group of stars at a certain point in the sky.  But as the hours passed, some people may notice that this same group of stars may have moved their position in the sky.  This effect makes people think that constellations or groups of stars are moving across the night sky.

The most common explanation for the perception that these constellations are moving across the sky points to the Earth’s rotation with respect to its placement around the sun.  If one would observe the sunrise and sunset, for example, one would know that the sun rises somewhere in the east and sets at the opposite side which is the west.  This simply means that the sun’s placement during the day may seem like it changes with its supposedly highest point above the Earth at noon.  This concept holds true for the stars.  As the hours pass by, these stars may seem to have moved their positions.  This effect is a result of the Earth’s rotation which gives us night and day.

Other experts also explain it in a somewhat different way but with the same idea of the Earth’s position at different times or orbits around the sun.  As the Earth revolves around the sun, it changes orbit, and a different view of the stars is seen at each orbit, interval, or space.  This will then cause people to see the constellations as sweeping along the night sky when, in fact, it is the Earth that’s moving.  The sun and the stars actually remain where they are anytime of the day.  Their position remains constant while the Earth moves around them.  But the Earth’s movement is not noticeable  so people don’t realize it that what they are standing on is what’s moving and not the constellations above them.