Gravity and orbits

Gravity is an attractive force between any two masses. It is stronger when the masses are bigger and weaker when they are further apart. The Sun's enormous mass means its gravity holds the planets in their orbits. The Earth's gravity holds the Moon in orbit and gives us our weight.

An orbit happens when an object moves fast sideways while gravity pulls it towards the centre. Without gravity it would fly off in a straight line; without sideways speed it would fall straight in. Weight depends on the gravitational field strength: about 10 N/kg on Earth and 1.6 N/kg on the Moon. So weight = mass × gravitational field strength. Your mass stays the same everywhere.