Galileo and Newton

A random bit of common-knowledge correction... A oft repeated little myth is that Galileo died in the year Newton was born and sometimes this is given mystical significance: reincarnation must be afoot! (I came across this myth again - sans mystical interpretation - in Isaacson's Einstein: His Life and Universe). This case, however, bears out the maxim that things are always more complicated that they at first appear.

The problem, you see, is that for the Julian calendar a year is on average 365.25 days long, but a tropical year is in fact 11 minutes and 14 seconds less than that, which means the calender becomes progressively more out of sync with the seasons. The solution was calendar reform and the adoption of the Gregorian calendar. That calendar, however, is so named after Pope Gregory XIII who ordered the reform by Papal Bull in 1582 - but of course the Protestant Reformation had started in 1517, which meant that only some European countries adopted the calendar right away. Catholic Italy (where Galileo was born and died) adopted the new calendar as ordered in 1582 but Protestant Great Britain (where Newton was born) only adopted the calendar in 1750. So here comes the trouble: Newton was born on December 25th 1642 on the Old Style (i.e. Julian) calendar and Galileo died January 8th 1642 on the New Style (i.e. Gregorian) calendar. Newton's corrected date of birth (i.e. his New Style date of birth) is 4 January 1643, just under a year after Galileo's death and not in the same calendar year.

To rational people, of course, none of this really matters: even if Newton had been born in the same Calendar year as Galileo died, there would be no reason to think anything paranormal was going on, there just has to be many such coincidences in history. Nonetheless, the Newton-Galileo story is a nice little example of how complicated the world is and how even a book as carefully fact-checked as Isaacson's may contain errors. Skepticism, no matter the source, is always advisable.