Lectures / 08/06/2009 7:30 pm

Kepler and Dark Matter

Kepler’s famous Third Law provides a description of the orbits of the planets in our solar system. This law is based on the preeminence of our central star, the Sun, which contains by far the greatest mass of the solar system. It seemed a foregone conclusion that the same law of planetary motion also applied to the system of the Milky Way. However, on closer inspection in the course of the last century astronomers realized that this was not the case. The stars orbit round the centre of the Milky Way faster than is warranted by Kepler’s law. In 1976 this led to the postulate of an additional source of attraction in the form of “dark matter”, whose properties are still the subject of speculation among astrophysicists.