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Why
doesn't the North Star ever appear
to move in the sky as other stars do?
Sailors have used the North Star (Polaris) since early times to
navigate, since it
remains in a relatively fixed location in the northern sky. If you
view Polaris from
various points around the Northern Hemisphere, you will be facing
almost due north.
Actually, all stars are set in a fixed position in the sky relative
to each other. It is the
movement of the Earth, rotating on its axis, that makes the stars,
including the sun,
appear to move across the sky. (Planets, however, do move on their
own
through the sky and can thus be differentiated from stars.)
The
North Star is situated directly above the northern axis of Earth.
Thus,
as Earth spins, Polaris, on the northern pivot point of rotation,
does not appear
to move from its polar position. Hence the name Polaris.
Over
the millennia, all the stars are shifting in relation to Earth,
due to a
phenomenon known as precession. The direction that Earth's axis
is pointing is
slowly, almost imperceptibly, changing, in much the same way that
a spinning
top leans one way and then another. This precession occurs because
Earth
is not a perfect sphere, but is about twenty-seven miles wider in
diameter at
the equator than between the poles. The bulge in the middle is caused
by Earth's
rotation. Earth's slow wobble traces out a circular pattern in the
sky, and it
takes twenty-six thousand years to complete one circle. For this
reason,
Polaris will not always be the "North" Star. In about
fifteen thousand years,
the star Vega will take the place of Polaris in the northern sky.
By A.D. 27,990,
Polaris will return to its present position as the North Star.
It
is easy to find the North Star. Locate the Big Dipper.
Form a line between the two pointer stars, follow it north to Polaris.
From
... "The Thoughts for the Throne" by Don Voorhees
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