A documentary available for the next 7 days -
http://www.bbc.co.uk/iplayer/episode/b008d2x7/The_Comets_Tale/
It seems fairly comprehensive, though it sticks to the dirty snowball model and perhaps doesn't emphasize enough the danger of a large number of comet fragments and rubble hitting the earth, osit. (Just a small section about the world wide event in 540 AD).
http://www.bbc.co.uk/iplayer/episode/b008d2x7/The_Comets_Tale/
It seems fairly comprehensive, though it sticks to the dirty snowball model and perhaps doesn't emphasize enough the danger of a large number of comet fragments and rubble hitting the earth, osit. (Just a small section about the world wide event in 540 AD).