Leap Year - Why ??
Dr. Mahbub Khan
Tomorrow, Saturday, February-29-2020 is a leap year day. The question is why is this extra day on February 29, tomorrow? The answer is very simple, but I think it is very important for all of us to understand why do we have this extra day in February 2020.
Before I explain the reason for Leap year, let me first explain why it is called "Leap" year. The word Leap means Jump over or Spring over or skip over. There are 365 days in a year and 7 days in a week. So, if we divide 365 by 7, we get 52 (weeks) and one day as remainder as 365/7 = 52R1. So, if January 1 is a Monday in some year, the following year the January 1 is a Tuesday because of the remainder 1 day. However, if there is a Leap year, then the following January 1 Leaps over Tuesday and it falls on Wednesday. That is why it is called the Leap year because it causes the jump or Leap by that 1 day.
All objects in the universe are continuously moving non-stop. The stars, planets, moons, galaxies, black-holes, dark-matter, asteroids, comets and all other heavenly space objects and bodies are moving in a very complex way, including spinning, orbiting, precessing, in addition to some linear motion components as well. The same is true for our solar system objects, including our very dear planet Earth, our home. Here is a brief description of the cause of the leap year day, the February 29.
Our planet Earth takes 365 days 5 hours and 48 minutes to orbit the Sun completely, relative to the stars. So, after spinning 365 times giving us 365 days and 365 nights, the Earth still can not return to its original starting point on its race track. It needs another 5 hours and 48 minutes extra to come back to its starting point by continuing to spin. So, after 4 years this extra time of 5 hours and 48 minutes adds up to a little less than 24 hours, which is added to February as Feb-29 (leap-year day) in every 4th year. However the extra time does not quite add up to 24 hours in 4 years. So, to compensate for that deficit of spin-time, this extra day is not added after every 100 years. So, 2100, 2200, 2300 are not leap years, and the month of February has 28 days in those years, even-though those years are divisible by 4. However, it turns out from the calculation and the observation that the effect of not including the leap-year day in every 100 years is a little too much to throw away. So, after every 400 years, the leap-year day is added. So, the years 2000, 2400, 2800 years had and will-have 29 days in February as those years are divisible by 4 as well as by 400. This correction continues for another step for another longer period of time, which I am not including here.
There are various different interesting traditions that have evolved in various societies and ethnicity of the world over the centuries related to the celebration of the Leap-year day of February 29. The birthday celebrations and proposing for marriage are some of the highlights. Traditionally the boys propose to the girls for marriage on any day of the year, but the leap year day of February 29 is considered a day reserved for the girls when the girls propose to the boys for marriage !!!
I have included a video here on Leap year that describes very nicely the background of the Leap year, why it is called Leap year, and about many of the fun things that have been developed connecting to the Leap year day. Please watch this video and enjoy, and let me know if you have any questions.
Dr. Mahbub Khan
Professor of Physics and Astronomy
California State University and Colleges
Senior Scientist at IBM in Silicon Valley
IEEE Chairman of Silicon Valley (SCVS/SFBAC)