The problem
365.2422days in a real year
365days on the calendar
6hours short each year, almost
24days off after a century, without fixes
Without leap years, summer would slowly drift into the calendar months of winter.
The leap year rules
- Divisible by 4: leap year2024 and 2028
- Divisible by 100: not a leap year1900 was skipped, and 2100 will be
- Divisible by 400: a leap year after all2000 was a leap year
- Result: almost perfectOff by only one day in about 3,000 years
The missing days
| Year | Who | What happened |
|---|---|---|
| 46 BC | Julius Caesar | Started a leap day every 4 years |
| 1582 | Pope Gregory XIII | Thursday, Oct. 4 was followed by Friday, Oct. 15 |
| 1752 | Britain and the colonies | Sept. 2 was followed by Sept. 14 |
George Washington was born Feb. 11, 1731 on the old calendar; we celebrate Feb. 22 on the new one.
Remember
Next skipped leap year: 2100.
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Answer key
- How long is a real year?About 365.24 daysAbout 365.2422 days.
- Will the year 2100 be a leap year?NoCentury years are skipped unless divisible by 400.
- Was 2000 a leap year?YesDivisible by 400, so yes.
- In 1582, what day followed Thursday, October 4?Friday, October 15Ten days were dropped to fix the drift.
- Who started the leap day every 4 years?Julius CaesarCaesar's Julian calendar, in 46 BC.