This is a digital copy of an old drawing. It shows the Sun surrounded by four Earths. There are four Earths, one for each season. Original art by ndreas Cellarius (1596-1665).
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(c)1995 Visual Language, All Rights Reserved

As the World Turns

In our time, scientists (and most people!) know that the constellations seem to move across the sky because the earth rotates on its axis. What, you may ask, does the turning of the earth have to do with the constellations' motion across the sky? The answer is that the earth moves in a way that makes it look as if the constellations are moving. It is a case of apparent motion. In the case of the earth and the constellations the earth rotates, with us on it, from west to east. The constellations appear to move from east to west, moving "backwards" from the real rotation of the earth. Actually, instead of saying the constellations rise we should say that the earth has rotated so that we can see different constellations. Then, as the earth continues to rotate the constellations apparently move across the sky. We now know that it is us, on earth, that have moved. As the night progresses constellations that are near or below the ecliptic "set" in the west, we know that the part of the earth we are standing on has turned so that the Earth is blocking our view of the stars that have "set".

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