This week, on its way in towards the Sun, Halley's Comet is closer to Earth than it has been for 75 years. Even so, you'll need binoculars to see it or, far better, "Horizon". This celestial guide tells you what comets are made of, where they come from, how they are predicted and how dangerous they are. Past comets may have destroyed almost all life on Earth - yet without them mankind might never have evolved.

Plus: the winner of the space race to reach a comet first and the odd story of how Halley's Comet was rediscovered with the help of two razor blades.