# On This Day: Johannes Kepler

On this day in 1630, the German mathematician and astronomer Johannes Kepler died in Regensburg, Bavaria. He was, at one point, assistant to the great Danish astronomer, Tycho Brahe, and later served as imperial mathematician to three Holy Roman Emperors. He is held to be one of the great astronomers, and his laws of planetary motion, published between 1609 and 1619, are still used today to predict the orbital movement of bodies in the solar system. They are:

**Kepler’s First Law:**The orbit of each planet is an ellipse with the Sun at one of the two foci.**Kepler’s Second Law:**A line joining a planet and the Sun covers equal areas during equal intervals of time.**Kepler’s Third Law:**The square of the orbital period (the ‘year’) of a planet is proportional to the cube of the semi-major axis of its orbit (its furthest distance from the Sun).

In addition to his major contribution to the science of astronomy, Johannes Kepler also produced a work of ‘proto-SF’ which some consider to be the first work of science fiction. *Somnium*, an account of how the workings of the solar system might appear to an observer on the Moon, was written between 1620 and 1630, and published posthumously by his son, Ludwig.

**Mathematician, astronomer, SF author: Johannes Kepler, we salute you!**