**Kepler's laws** are a set of three laws that describe the orbits of bodies around a much larger body (for example, planets around the sun).

- The orbit of a body is a conic section, with the sun at a/the focus.
- The line between the body and sun sweeps out an equal area during equal time spans, regardless of where the body is in its orbit.
- The square of the orbital period is proportional to the cube of the semi-major axis (that is, the farthest the body is from the sun). This can be formulated as

- $ P^2 = \frac{4 \pi^2 a^3}{G(M+m)}\approx \frac{4 \pi^2 a^3}{GM} $