Sheldon declaims, "December 25th 1642 Julian calendar: Sir Isaac Newton is born. Jesus on the other hand was actually born in the summer." Leonard responds with characteristic sarcasm "Merry Newtonmas everyone!" According to my notes, Jesus was probably born in in the spring of 4 AD. Newton was indeed born on December 25th 1642 Julian calendar, which is January 4th 1643 Gregorian calendar.