Comet Kahooey passes by Earth in 1992.
Comet Kahooey was a comet that visited Earth once every 25 years. It lit up the skies over Hill Valley in both 1967 and 1992.
Emmett Brown built a flying craft to study the comet in greater detail, but Biff Tannen believed it to be an alien spacecraft. When Biff saw the craft hiding in the bushes 25 years later, he made the assumption that Doc must have been an alien.
Behind the scenes[]
Were the comet to return again 25 years later, it should make an appearance in 2017.