
So, I was wondering... wanting to know more about leap year, I wanted to know more about the history, like when did they figure out that they needed to do this... things like that. I understand it's done to keep the seasons in place with our calendar and not have them move so that one day in the future, we're having snow in July.
Here is some of what I found out...
Leap years are needed to keep our calendar in alignment with the earth's revolutions around the sun. Leap year is a semi convoluted thing since that we are trying to make up for an imperfect trip around our sun.
If we were to always kept a 365 day year, year after year, every year there would be a loss of 0.2422 days, or about six hours... hence every 4 years is 24 hours, or one day. It would take 100 years to move it 24 days ahead of season, or in other words over 100 years to see it get out of whack by a month.
This February has five Fridays, the last time that happened was in 1980 and the next will be in 2036.
So no calendars used today are perfect, they are off by seconds, minutes or hours per year. To make a calendar more accurate, new leap year rules have to be introduced to the Gregorian calendar, complicating the calculation of the calendar even more. It will, however, need some modifications in a few thousand years.
So we have the Gregorian calendar which was introduced in 1582 and decreed by Pope Gregory XIII who happens to be the namesake. The average year is 365.2425 days long, the approximate error introduced is 27 seconds... or 1 day every 3,236 years. With the Gregorian calendar there is a 400 year repeat cycle. SO... February 29th, 2008 is a Friday and February 29th, 2408 will be a Friday. In other words (I think) that if we took the 2008 calendar and the 2408 calendar and put them side by side, then every date and day would match up.
In the Gregorian calendar, the calendar used by most modern countries, the following three criteria determine which years will be leap years:
- Every year that is divisible by four is a leap year;
- of those years, if it can be divided by 100, it is NOT a leap year, unless
- the year is divisible by 400. Then it is a leap year.
According to the above criteria then, that means that the years 1800, 1900, 2100, 2200, 2300, and 2500 are not leap years... 2000 and 2400 are.
It is interesting to note that 2000 was somewhat special as it was the first instance when the third criterion was used in most parts of the world. Not every country is on the Gregorian calendar.
In the Julian calendar–introduced by Julius Caesar in 45 BC and patterned after the Roman calendar–there was only one rule: any year divisible by four would be a leap year. This calendar was used before the Gregorian calendar was adopted. In the Julian calendar the average year is 365.25 days and is off by 11 minutes every year... one day every 128 years. The Julian calendar introduced too many leap days, thus increasing the number of days between the vernal equinox of March 21, its scheduled date as noted in AD 325 during the Council of Nicaea. The introduction of the Gregorian calendar allowed for realignment with the equinox; however, a number of days had to be dropped when the change was made.
A calendar similar to the Julian calendar, with every fourth year earmarked as a leap year, was first introduced by King Ptolemy III of Egypt in 238 BC.
I also came across something that pointed out that the Mayans had figured it out before the Egyptians. I don't know, I was not around for either.The Gregorian calendar was first adopted in Italy, Poland, Portugal and Spain in 1585. This was done by dropping 10 days in October of that year.
In Great Britain (and America), the Gregorian calendar would not be adopted until much later, in September 1752; 11 days were dropped.
How about February 30th... ? There was one. Sweden (and Finland) had a "double" leap year in 1712. Two days were added to February–creating a date of February 30, 1712. (This was done because the leap year in 1700 was dropped and Sweden's calendar was not synchronized with any other calendar. By adding an extra day in 1712, they were back on the Julian calendar.)
Missed the first one and won't be around for the next one... The longest time between two leap years is eight years. The last time that occurred was between 1896 and 1904. The next time will be between 2096 and 2104.
I read that in 48 B.C., Julius Caesar was in Alexandria, Egypt, absorbing the culture and science — and decadence — of Cleopatra's capital. There he learned from an old sage named Acoreus about Egypt's calendar, which had a leap year. At the time, the Roman calendar did not. Like most ancient calendars, it was based on the phases of the moon, which in one cycle takes about 29.5 days. But 12 months of 29.5 days doesn't equal the true length of the year as measured by the orbit of the Earth around the sun. It's off by 11 days, so anniversaries, holidays, and entire seasons drifted backward on lunar calendars. The ancient Egyptians had realized this and created a calendar 365 1/4 days long — with the fraction averaged in by adding an extra day every four years.
When Caesar returned to Rome, he created a 365-day calendar with a quadrennial leap year, adding the extra day in February. A minor hassle for some, perhaps, but certainly better than the alternative faced by the Romans. Back in 45 B.C., for instance, their lunar calendar had drifted backward by 80 days — nearly three months. Spring had become winter, and autumn came in the summer months. To correct this, Caesar decreed that 45 B.C. would be 445 days long.
I'm somewhat amazed that as far back as 238 BC they figured it out, though I guess they had a lot of time of their hands to figure this stuff out.
Well, there's much more on the subject and I found it fascinating... but the hour now as I finish this up (and not the 9:41 time at which I started this) is late and I need to stop.
Until the next leap.






