# Johannes Kepler Facts

• Johannes Kepler (1571-1630) was the German astronomer who discovered the basic rules about the way the planets move.
• Kepler got his ideas from studying Mars’ movement.
• Before Kepler’s discoveries, people thought that the planets moved in circles.
• Kepler discovered that the true shape of the planets’ orbits is elliptical (oval). This is Kepler’s first law.
• Kepler’s second law is that the speed of a planet through space varies with its distance from the Sun.
• A planet moves fastest when its orbit brings it nearest to the Sun (called its perihelion). It moves slowest when it is furthest from the Sun (called its aphelion).
• Kepler’s third law is that a planet’s period — the time it takes to complete its yearly orbit of the Sun — depends on its distance from the Sun.
• Kepler’s third law states that the square of a planet’s period is proportional to the cube of its average distance from the Sun.
• Kepler believed that the planets made harmonious music as they moved — ‘the music of the spheres’.
• Kepler also wrote a book about measuring how much wine there was in wine casks, which proved to be important for the mathematics of calculus.