Why Leap Year?

(4 Minute Read. 28Feb2024)

Happy Leap Day!
February 29
American Bullfrog

What was the longest calendar year in history?

You might guess that it’s a leap year of 366 days, but you would be wrong.

One particular calendar year was actually a great deal longer — several months longer! Once in history, a calendar year was 445 days long! A true jumbo year.

How and why did this happen?

Were calendar years ever shorter than 365 days?

Yes; several were only 355 days long.

How and why did this happen?

Calendar Years and Solar Years

Nowadays we usually think of a year as 365 days, and most calendar years are exactly this long. But the solar year, the time it takes Earth to orbit the sun, is slightly longer than the 365-day calendar year. The solar year is 5 hours, 48 minutes, and 56 seconds longer; that is, the solar year is 365.242190 days long, just short of 365 and a quarter days.

Thus occasionally time needs to be added to the calendar year in order to keep the calendar in sync with the seasons — which are determined by the solar year. This is the reason for Leap Years which add time to the calendar year in the form of Leap Days on February 29.

For example, if time were not added to the calendar year, then in around 700 years the calendar’s relation to the solar cycle would have shifted so much that the Northern Hemisphere’s summer would begin in calendar December instead of calendar June.

Leap Years occur every four years in years divisible by 4 except for end-of-century years, which must be divisible by 400. For example, 2016, 2020, 2024, and 2028 are leap years as was the end-of-century year 2000. But 1900 and 2100 are not leap years.

If the solar year were exactly 365 and a quarter days, then adding a Leap Day every four years would keep the calendar and seasons in sync. But since the solar year is slightly less than 365 and a quarter days, occasionally the fourth year is not a leap year, namely when the end-of-century year is not divisible by 400.

The current year, 2024, is a Leap Year. Tomorrow, February 29, is the extra day added into the year at the end of February. Instead of having 365 days, 2024 will have 366.

Why the Term “Leap”?

Normally, in 365-day years, a specific date only moves forward by a single weekday from one year to the next. This is because 7 divided into 365 is 52 with a remainder of 1. That is, a non-leap year is 52 weeks and 1 day long. For example, Christmas Day, December 25, was on Sunday in 2022 and on Monday (one day forward) in 2023.

In leap years, starting in March following the leap day of February 29, each calendar date “leaps” forward an additional weekday from the preceding year because 366 divided by 7 is 52 with a remainder of 2. That is, a leap year is 52 weeks and 2 days long. Thus Christmas Day in 2024 will not be Tuesday (one day forward from 2023), but it will “leap” over Tuesday to be Wednesday (two days forward from 2023). January and February dates will do their “leaps” in 2025.

Leap Years in the Bible?

It is interesting that Noah’s records of time during the Flood show his months had 30 days. The Flood began on the 17th day of the second month of Noah’s 600th year. At the end of 150 days, in the seventh month, on the 17th day of the month, the Ark came to rest on Mt. Ararat. Five months lasted exactly 150 days, for 30 days per month. (Genesis 7:11; 7:24-8:4)

Thus it is possible that in the beginning there was no need for leap years. It’s possible that months were 30 days long and years were 360 days long. The upheavals associated with the Flood, both causative and resultant, may have slightly altered the orbits of the moon and earth so that they were no longer so perfectly aligned as originally created.

The Longest and Shortest Years

When Julius Caesar (100 BC – 44 BC) rose to power in the Roman Empire, the Roman calendar was badly out of sync with the seasons. The Roman calendar was based on the moon, and 12 lunar months is about 11 days short of a solar year. A lunar month is the time it takes the moon to orbit the Earth, and 12 lunar months is 354.36 days. Roman harvest festivals based on the Roman calendar no longer fell at harvest time.

Caesar added days to the calendar in 46 BC to fix the discrepancy. He made 46 BC 445 days long. Thus 46 BC is the longest calendar year in history.

The next year, in 45 BC, Caesar instituted the Julian calendar of 365 days divided into 12 months with an additional leap day every fourth year. Thus we have Julius Caesar to thank for Leap Years and Leap Days.

The Julian calendar worked well for hundreds of years, but by the mid-1500s the seasons began about 10 days earlier than indicated by the calendar because the solar year is slightly shorter than 365 and a quarter days. The Julian calendar runs one day ahead of the solar year every 129 years, or 3.1 days every 400 years.

To fix this, in 1582 Pope Gregory XIII (1502–1585) introduced the Gregorian calendar that we use today. He took out three leap days every 400 years by excluding leap years in end-of-century years not divisible by 400. He also took 10 days out of the year by having Thursday, October 4, 1582, be followed by Friday, October 15, 1582, to correct the drift of the Julian calendar. Thus 1582 was the shortest calendar year in history with only 355 days. The Gregorian calendar also changed the start of the year to be January 1.

Gradually the Gregorian calendar was adopted worldwide — but slowly. Great Britain and the American colonies only adopted it in 1752 and synchronized calendars by following Wednesday, September 2 with Thursday, September 14. Since 1752 was a leap year, this calendar year also had only 355 days.

The Gregorian calendar runs one day ahead of the solar year every 3,030 years. Maybe in a few millenia, to correct this a leap day will be skipped in some year. A BibleScienceGuy Blog article in the year AD 4612 might answer the question, “Why didn’t we have a February 29 leap day this year?” Maybe that article would propose a slight modification to extend the validity of the Gregorian calendar by eliminating leap years in years that are integer multiples of 3,000.

But maybe the Lord Jesus Christ will return to Earth before then and the issue will be moot. Let’s hope so!

Questions to Ponder

1. Do you know anyone born on February 29? Do they age slower than you since they only have birthdays every four years?
2. When people discuss leap year, how can you honor the Great Creator in the conversation?

Share your thoughts on these questions in the comments below. It could encourage or help another reader.

For Christ and His Kingdom.
Alere Flammam Veritatis.
Soli Deo Gloria.

Read the prequels in this Why? Series:
Why Is the Age of the Earth Important?
Why Apologetics?
Why Do Atheists Care?
Why Did Adam Sin?
Why Should Adam’s Sin Affect Me?
Why Do Leaves Change Color?
Why Do I Write the Bible-Science Guy Blog?
Why Is Ice Slippery?
Why Does Salt Melt Ice?
Why the Virus?
Why Is Christmas December 25?
Why the Week?
Why Do Clocks Run Clockwise?
Why Light?
Why Water?
Why Oxygen?
Why Carbon?
Why Nitrogen?

Read the sequel:
Why Stars?

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©William T. Pelletier, Ph.D.
“contending earnestly for the faith”
“destroying speculations against the knowledge of God”
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(Jude 1:3; 2 Cor 10:5; Phil 1:16)
Wednesday, February 28, 2024 A.D.

In the beginning God created the heavens and the earth. (Genesis 1:1)

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