Expert: Jayendra Upadhye - 3/20/2006

Question
Hello,
here is my question that hopefully makes sense.
If the moon orbitted the Earth at the same rate that the Earth turned on its axis, would the moon always be on the same side of the Earth? Like, could the moon always be on the North American side? Is this what happens with Pluto and Charon?


Answer
Hi,
Heather, for that to happen, the earth's gravity would have to be very strong, to counteract the centripetal tendency of the moon at that higher orbital velocity. (It would have to go about the earth in 24 hours, in place of 28 full 24 hour days!

But if that were to happen miraculously, what you say would be true.

For the earth, this distance is the geostationary orbital radius @36,000 km.

Most communications satellites reside there.

About charon i do not know, most probably, it is phase-locked with pluto, like our moon is with earth, keeping one side all the time to the earth!

So for lunar guys, the earth would always be stuck to one position over the horizon, depending on where you happened to live on the moon!

Because, the moon always keeps same face turned to the earth, or turns once around itself every month! (28 days approx)

search about tidal locking of satellites on the web.
As a result of this lock, the moon is speeding up in its orbit and receding away at 4 cm / year approx,
Jayen