the reason why isaac newton's birth date have two different sayings

Isaac Newton's birth date has two different sayings due to the historical context of calendar systems used at the time:

1. Julian Calendar: Isaac Newton was born on December 25, 1642, according to the Julian calendar, which was in use in England until 1752.

2. Gregorian Calendar: However, the Gregorian calendar, which is the calendar system most commonly used today, places his birth date a day later, on December 25, 1642, in the Gregorian calendar.

The reason for the difference is that the Gregorian calendar was introduced by Pope Gregory XIII in 1582 to correct inaccuracies in the Julian calendar's calculation of the length of a year. The Julian calendar assumed a year to be 365.25 days long, while the Gregorian calendar recognizes a slightly shorter length, accounting for leap years more accurately.

England and its colonies did not adopt the Gregorian calendar until 1752, when the Calendar (New Style) Act came into effect. This shift mandated moving forward in the date by 11 days to align the calendar with the astronomical year more closely.

So, while Newton was born on December 25 in the Julian calendar, the conversion to the Gregorian calendar would place his birth date as January 4, 1643, as per the Gregorian calendar. This is why you might see two different dates associated with Newton's birth. However, it should be noted that December 25 is the more widely recognized and celebrated date for his birth.