How scientist have calculated the size and weight of the earth, moon and the sun?
Once Newton had calculated the “universal” gravitational constant and provided an equation to calculate orbital periods, it was noticed that the orbital speed of a small body depends only on the mass of the central body. It was possible to measure Earth’s orbital speed (orbital circumference divided by the time it takes to cover one year), which gives the Sun’s mass. Once you know the distance from Earth to Moon, you can calculate the Moon’s orbital speed and we know its orbital period (a sidereal month), this gives us the Earth’s mass. The Moon was a bit trickier, since nothing small is in orbit around the Moon. However, it is possible to consider both Earth and Moon in orbit around their common centre of mass (called the barycentre). This causes Earth to wobble around the barycentre and that can be calculated (but it could not in Newton’s days). Another effect that depends on the Moon’s mass: the tides on Earth. We have two tide systems, the major one caused by the Moon, the other ca
