The Simplified Science Behind Leap Years

Why are we here today?

It doesn’t take 365 days for the Earth to orbit the sun, it takes 365.25 days.
To keep our 12-month calendar accurate, we round down to 365 days and save the extra hours for leap year.
Since .25 days multiplied by 4 equals 1 full day, we add a day to our calendar every year.
Leap day is in February because it is customary. We could add it to any month, but we add it to February since it is the shortest month.

Because after hundreds of years without leap years, instead of summer beginning around June, it would start in November. Our current understanding of the connection between months and their relation to seasons would be majorly disrupted. For example, when we choose to grow certain foods.

The earth does not revolve around the sun exactly 365.25 times a year. The accurate number is slightly less at 365.2422 times.
Adding an additional day every 4 years is a slight overcompensation of time.
To solve this overcalculation, we do not recognize a leap day on years when the following year characteristics exist:
- We enter a new century AND
- The new century is divisible by 100 and not by 400.
We witnessed a lack of leap years in the years 1900 and 1800, but not in 2000 because of this.