This is part of the Royal Institution Christmas lectures delivered by Carl Sagan in 1977. It is incredible to see those fuzzy pictures of Jupiter's moons - we have now been completely spoiled by Voyager and more recently by images from the Galileo spacecraft. In any case, here is the first part of the first lecture (tip Cosmic log). It is great to see a number of young kids in the audience - don't know how many ended up being astronomers. Enjoy!
Here are links to the other parts of the first lecture: part 2, part 3, part 4, part 5, and part 6 (why not put all of them in one link??)