The Sun pulls on the Moon with about twice the force that the Earth pulls
on it. So why doesn't the Moon get pulled away from the Earth? I realize
this is complicated. Is there a "simple" explanation I can tell high school
students?
I searched online. One site said that the Moon's orbital velocity (1 km/s)
is simply less than the Earth's escape velocity (1.2 km/s) at the Moon's
distance from the Earth. Not sure how they came up with this 1.2 number.
Several sites mentioned the Hill sphere (never heard of this before). I
guess if an orbiting object is within a certain distance of a central body
(e.g., Earth), the gravity dominates that from a more distant body (e.g.,
Sun). Is this related to the Roche limit?