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- [Narrator] This is
a computer made movie.
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The box represents a satellite,
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which is now in a circular
orbit going over the pole.
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In the upper right, a clock
counts off the number of orbits.
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Gravity gradient torques force
the satellite's long axis
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to point toward the earth.
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Exactly this effect keeps one face
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of the moon always
pointing toward the earth.
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This is very useful for weather
or communication satellites
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where either an Earth-pointing camera
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or an Earth-pointing antenna is desired.
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In the rest of the movie,
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we should look at the satellite
only in a reference frame
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that is orbiting as the
satellite is doing now.
