Astronomers have this month trained the world's largest steerable radio telescope on 86 Earth-like planets. The data collected by the telescope will later be analsyed by an estimated one million amateur alien hunters, users of SETI@home, for messages from other civilisations.

We take reliable radio communications for granted, but accommodating many different users is not easy. Robert Leese explains how the mathematics of colouring graphs can help avoid interference on your mobile phone.