Image: (c)1995 Visual Language, All Rights Reserved
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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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