Why can you learn more about the shape of earth by studying the motion of an artificial sateliite than by studying the motion of moon?

Answer 1

-- An artificial satellite can be operated and observed in a 'polar' orbit, in which

it eventually overpasses every point on Earth, or in any other desired orbit. The

moon's orbit is inclined about 5 degrees to the plane of the ecliptic, which is a

nice orbit, but that's where it stays. So there's a full 62-degree 'cap' around both

the north and south poles, where the moon can never be overhead.

-- An artificial satellite can be operated and observed in an orbit with any desired

eccentricity, and the eccentricity can be controlled and modified at will. The moon's

orbit has a mean eccentricity of only 0.055, and the orbit has many irregularities and

perturbations, which have been studied for many years.

-- For each revolution of the Moon, the Earth rotates inside the Moon's orbit 27.32 times.

The orbit of an artificial satellite can be adjusted so that for each revolution, the Earth

rotates within the satellite's orbit any number of times, from zero and on up.

-- Since the mass of any artificial satellite is so much less than the mass of the

moon, and since most artificial satellites spend most of their time nearer to Earth

than the Moon is, small local irregularities in the shape of the Earth's gravitational

field have a much greater influence on the orbits of the artificial ones.