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The outer limits of the solar system are a dark, cold and mysterious place, which only the Voyager spacecraft have visited. Sir Patrick Moore discusses the ice giants Uranus and Neptune, while Chris Lintott has an early Christmas treat - a lost episode of The Sky at Night from 1963 which has been returned to the BBC, in which Arthur C Clarke talks about his vision of bases on the moon and speculates when man will be on Mars.
Other episodes for this season