Expert: Steven LJ Russo - 3/28/2005

Question
I understand that the moon rotates around the earth once every 28 days or so.  But, it does not spin like the earth.  So the same face always faces the earth.

I understand it is the earths gravity that locks it in place.  I guess it does not have to spin because of that.

My question: if the gravity pull is so strong between earth and the moon to hold it in place and effect tides etc, how come when people go into space between the earth and the moon, they enter into gravity free space, and float around?

Thank you,

Richard

Answer
Rich:

The moon revolves around the Earth once every 28 days (number rounded off slightly), AND, it also rotates around it's axis in 28 days.  Which is why the same side always faces the Earth.

A common misconception among people is "gravity free" space.  There is no such thing.  Gravity is in EVERY square inch of the universe.  We sometimes hear the astronauts talk about "Zero-G", but that is just a term we use in the profession.  There is no such thing as Zero Gravity.  Its microgravity.  Folks don't actually "float", as they are actually being "pulled" around the Earth by ot's Gravity, or by the Moon's gravity.

Apollo 8 was the first manned craft to leave the Earth's gravity, and when it did, it was then being "pulled upon" by the Moons Gravity.  That's also why in Apollo 13 (watch the movie), the NASA folks decide to keep the craft going, to be pulled in by the Moons gravity, which then would "slingshot" it around the Moon and back to earth.

Steve