The Cosmic Distance Ladder

How do we know the distances from the earth to the sun and moon, from the sun to the other planets, and from the sun to other stars and distant galaxies? Clearly, we cannot measure these directly. Nevertheless, there are many indirect methods of measurement, combined with basic high-school mathematics, which can allow one to get convincing and accurate results without the need for advanced technology. These methods rely on climbing a “cosmic distance ladder”, using measurements of nearby distances to then deduce estimates on distances slightly further away.

You can learn more about Terence Tao at https://www.math.ucla.edu/~tao/