20 June 1964: broadcast of "Strangers in Space", first episode of the story we now call The Sensorites. The Tardis lands on a spaceship whose crew have been incapacitated by the mysterious Sensorites.
20 June 1970: broadcast of seventh episode of Inferno, ending Season 7 of Old Who; last regular appearance of Caroline John as Liz Shaw. The Doctor and Liz prevent the drill from breaking through the crust; Stahlman is completely transformed into a Primord and is restrained.
20 June 1991: publication of Timewyrm: Genesys by Terrance Dicks, first in the run of New Adventures published by Virgin.