the two different sayings of isaac newton birth date are december 25 1642 and january 4 1643

Isaac Newton's birth date has two different notations due to the calendar system in use at the time. Here's the explanation:

1. December 25, 1642: Newton was born on this date according to the Julian calendar, which was in use in England at the time of his birth. The Julian calendar was introduced by Julius Caesar in 45 BCE and was the predominant calendar in Europe until it was replaced by the Gregorian calendar.

2. January 4, 1643: This date corresponds to the transition from the Julian to the Gregorian calendar. In 1582, Pope Gregory XIII introduced reforms to the Julian calendar to correct inaccuracies in its calculation of the solar year. The Gregorian calendar was adopted by different countries over time. England did not adopt the Gregorian calendar until September 1752.

When England finally switched to the Gregorian calendar in 1752, they skipped 11 days to align with the solar year. As a result, September 2, 1752 was followed by September 14, 1752. Additionally, the start of the year was moved from March 25 (Lady Day) to January 1, so dates between January 1 and March 24 were effectively shifted forward by one year.

So, when historians updated Newton's birth date to the Gregorian calendar, they adjusted for both the skipped days and the change in the start of the year. Newton's birth date of December 25, 1642 (Julian) became January 4, 1643 (Gregorian).

In summary, Isaac Newton was born on December 25, 1642, according to the Julian calendar used in England at the time. When this date is converted to the Gregorian calendar, it becomes January 4, 1643. Both dates are correct, but they refer to different calendar systems that were in use at different times.