"All Our Yesterdays" is a third season (and the penultimate) episode of the science fiction television series, Star Trek, first broadcast March 14, 1969, and repeated on August 5, 1969. It is episode #78, production #78, written by Jean Lisette Aroeste, and directed by Marvin Chomsky. It guest-stars Mariette Hartley as Zarabeth. The title comes from a well-known soliloquy given by Macbeth in Act V Scene V. In this episode, Kirk, Spock and McCoy are trapped in two parts of another planet's past—a world threatened with destruction when its sun goes supernova.