Mass of the Earth
Since gravity depends on the masses of both objects, we can look at how strongly the earth attracts the moon. It is the earth’s gravitational attraction that keeps the moon going around the earth, rather than the moon going straight off into space.
By looking at how fast the moon orbits the earth at its distance from the earth, we can get the mass of the Earth: 6 x 1024 kg, equivalent to 600 billion trillion tons.