Halley's Comet
From Tardis Wiki, the free Doctor Who reference
Halley's Comet is a comet of the sol system and is the only comet that can be seen by the naked eye when it approaches Earth every 75 to 76 years. On Earth Halley's Comet is always associated with impending disaster.
Time traveling to 1985, the Cybermen planned to divert Halley's Comet so that it would destroy Earth. This way, the Cyberman home planet of Mondas would not be destroyed when it approached Earth in 1986. They were stopped by the Doctor. (DW: Attack of the Cybermen, The Tenth Planet)
