 CHAR: As Doc Brown is showing Marty how the time machine works, he  gives examples of certain important dates in history that you can  travel to. One of them is the birth of Christ, which he enters "DEC  25 0000". There is no year between 1 B.C. and 1 A.D. It is believed  that Christ was actually born in 1 A.D. It is also believed that  Christ was born sometime in the spring.