Kepler's Laws of Planetary Motion Three laws, based on precise observations of the motions of the planets by Tycho Brahe, which summarize the motions of the planets about the Sun.

Kirchhoff's laws Three rules governing the formation of different types of spectra.

Kirkwood gaps Gaps in the spacings of semi-major axes of orbits of asteroids in the asteroid belt, produced by dynamical resonances with nearby planets, especially Jupiter.

Kuiper belt A region in the plane of the solar system outside the orbit of Neptune where most short-period comets are thought to originate.