Mysteries of the Winter Sky

The winter sky is magnificent, with Orion dominant; this year there are also two of the brilliant planets, Jupiter and Mars. But there are puzzles to solve, too. For example, why was Sirius once described as a red star rather than a white one - and has Alcor, the companion to Mizar in the Great Bear, brightened since ancient times? Patrick Moore takes a look round the winner sky, and discusses some of these curious mysteries.