Hey, I Haven't Finished!
The Earth hasn't finished its lap when the calendar reaches 31 December.
Click to zoom
When the calendar says the year is over, the Earth still needs about a quarter of a day.
See how 0.2422 of a day adds up over centuries, and why leap years follow the rules for 4, 100 and 400.
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A year on the calendar is shorter than the Earth's trip around the Sun.
The Earth takes 365.2422 days to go around the Sun. Our Gregorian calendar year has 365 days.
After one calendar year, the Earth still needs 0.2422 more days to finish its trip.
The Earth hasn't finished its lap when the calendar reaches 31 December.
When the calendar says the year is over, the Earth still needs about a quarter of a day.
Checking the every-4-years fix with decimal multiplication.
Problem. With one leap year every 4 years, how close is the calendar to the Earth, over 4 years and over 100 years? (Textbook p. 89)
Questions on the every-4-years rule.
With no leap days at all, how far behind is the calendar after 100 years?
Skip the leap day in century years, except every 400th year.
No extra day in years divisible by 100. In 100 years that leaves 24 leap years and 76 common years:
Very close to 36,524.22.
How many leap years are there in 1000 years with all three rules?
Problem. With the final rule, how many days are in 1000 calendar years? (Textbook p. 92)
Test the final rule over 10,000 years and suggest a fix.
Try This, Textbook p. 92. With the final leap-year rule, how many calendar days are there in 10,000 years? How many days does the Earth need for 10,000 trips around the Sun? What is the difference? If it is big, suggest a fix.
Divisible by 400; by 100 but not 400; by 4 but not 100.
365 × 10,000 + leap days.
10,000 × 365.2422.
Which is longer, and by how much?
How would you remove the extra days?