Yes, it's almost Leap Year again, and this February 2012, we are graced with an extra day - February 29. Sweet - one more day to do whatever you want - whether that is work, play or sleep - you choose.
We are usually graced with this extra day to celebrate approximately once every 4 years...but read on to learn about the origins and calculations and trivia about Leap Years. You'll find, it's not quite as simple as they may have taught us in school.
What is a leap year?
A leap year consists of 366 days, as opposed to a common year, which has 365 days. We account for this by making February 29 days (rather than 28 days).
Why do we have leap year (or a leap day)?
The need for a leap year is help synchronize the calendar with the actual revolution of the earth. A typical year is 365 calendar days while the actual revolution of the earth around the sun is about 365.25 days (actually it's 365.242374 days long to be exact and this amount slightly increases each year).
So, if we left the calendar without a leap day, the time of year/seasons would eventually be off and the official start of spring or the spring equinox (when the there is equal amount of lightness and darkness) would start coming earlier and earlier in the year. Over a 100 year time period, that would translate to our calendar shifting by 24 days vs. the seasons we are accustomed to.
So, instead, every 4 years, we add an extra day - a Leap day - to help get the calendar in synch w/ the actual motion of the earth.
Now, remember how I mentioned that an actual physical year is 365.242374 days? Well, 365.24374 is slightly lower than 365.25, so if we continued the simple process of just adding 1 day...eventually, we would jump ahead. So, to counteract that, the official rule is that we have a leap year every 4 years (years divisible by 4) such as 2012 2016, 2020, etc UNLESS that number is also divisible by 100 (such at 1700, 1800 or 1900) and EXCEPT if that number is divisible by 400 (such as 2000, 2400).
Therefore, in a duration of two millennia (or 2000 years, there will be 485 leap years. By this rule, the average number of days per year will be 365 + 1/4 − 1/100 + 1/400 = 365.2425, which is 365 days, 5 hours, 49 minutes, and 12 seconds. Now, this still isn't exact with 365.242374, but it's close enough.
It means that the marginal difference of 0.000125 days between the Gregorian calendar year and the actual year will result in us being behind by 1 day every 8,000 years. The current method works for practical purposes and there was a correction suggested by John Herschel making every 4,000 years a non-leap year. However, there are other factors at play here including that the earth's revolution is slowing slightly, so this may not actually be necessary.
So, just to sum up:
How to calculate Leap Years
In the Gregorian calendar, the following 3 criteria must be met to be a leap year:
- The year is evenly divisible by 4;
- If the year can be evenly divided by 100, it is NOT a leap year, unless;
- The year is also evenly divisible by 400. Then it is a leap year.
Who invented Leap Years?
Julius Caesar introduced Leap Years in the Roman empire over 2000 years ago. However, back then, they used the Julian calendar and they followed a more simple rule of using any year that was evenly divided by 4. This led to too many leap years and the issue was not rectified until around 1500 years later
Celebrity Leap Day birthdays
- 1468 – Pope Paul III (d. 1549)
- 1792 – Gioacchino Rossini, Italian composer (William Tell, The Barber of Seville) (d. 1868)
- 1916 – Dinah Shore, American singer (d. 1994)
- 1924 – Al Rosen, American baseball player
- 1924 – Carlos Humberto Romero, former president of El Salvador
- 1960 – Anthony (Tony) Robbins, American motivational speaker
- 1964 – Lyndon Byers, Canadian hockey player
- 1980 – Chris Conley, American musician and songwriter/composer
People born on February 29 are all invited to join The Honor society of Leap Year Day Babies.
Leap Year February 29, 2012 - Why do we have leap year and how is it calculated?
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