Horizon is a current and long-running BBC popular science and philosophy documentary programme.
Over 1,250 episodes have been broadcast (including specials) with an average of 23 episodes per series during the 56-year run.
Horizon Revisited was broadcast on BBC Four and shown between 2002 and 2003.
Each of the seven episodes takes information and clips from previous edition of Horizon and updates them with current thinking on each of the topics at hand.
These are similar in format to the current 'Horizon Guide' special episodes.