Isaac Newton was born on Christmas Day 1642 (Old Style)

Isaac Newton was born on Christmas Day, 25 December 1642, at Woolsthorpe Manor near Grantham in Lincolnshire. That is the date in England’s Julian (“Old Style”) calendar, and the one cut into his tomb in Westminster Abbey; on today’s Gregorian calendar the same day is 4 January 1643.

He was born into a broken household. His father, also Isaac, a prosperous farmer who could not sign his own name, had died in October 1642, three months before his son arrived. When the boy was two his mother, Hannah, remarried and moved to a nearby village, leaving him to be raised by his grandmother at Woolsthorpe.

A favourite piece of trivia says Newton was born in the year Galileo died, as if a torch passed straight from one to the other. The Galileo coincidence only works by mixing calendars. Galileo died at Arcetri, near Florence, on 8 January 1642, a date in the Gregorian calendar Italy already used. On that same calendar Newton was born on 4 January 1643, almost a full year later.

Put both men on England’s Julian calendar instead and Galileo’s death moves back ten days, to late December 1641. Only by pairing Galileo’s Gregorian date with Newton’s English one do the two events share the year 1642.

The farmhouse where he was born mattered again two decades later. When plague closed Cambridge in 1665, Newton went home to Lincolnshire and, in under two years and before he turned 25, began his revolutionary work on mathematics, optics and motion. He died in 1727 and lies in Westminster Abbey, whose Latin inscription still gives his birthday the old way: 25 December 1642.