Question:
At what altitude off the surface of the moon would a satellite be in
a stationary orbit over the moon?

Replies:
This is a neat question, but one which does not have a simple answer.
For an isolated planet we can work out the radius of a circular orbit with a
certain period. Top to be motionless, stationary the period must be 24 hours
for earth, while for the moon the period must be 28 days. The longer the period the farther away is
the orbit from the planet. For an orbit far away from the moon our satellite
would encounter the gravity of the earth and that would alter the orbit and make
a stationary orbit unlikely. Because of the earth's presence such an orbit is n ot possible. If
it were, you could use the value of the radius for earth and multiply it by the
one-third power of the ratio of the moon to the earth masses and multiply by the
two -thirds power of the number 28. That should give the value without the prese nce of the
earth. Let me know if this answer is confusing.

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.