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Science communication is important in today's technologically advanced society. A good part of the adult community is not science saavy and lacks the background to make sense of rapidly changing technology. My blog attempts to help by publishing articles of general interest in an easy to read and understand format without using mathematics. I also give free lectures in community events - you can arrange these by writing to me.

Sunday, 18 January 2009

Curious History of the Leap Year....

Leap years come every four years .. or do they?

A leap year has 366 days with the month of February lasting 29 days. 2008 was a leap year.

We are used to thinking that a leap year happens every fourth year. If the year is divisible by 4 then it would be a leap yaer. Not strictly true!

Actually: Every fourth year is a leap year.  But if the year is divisible by 100 then it must also bedivisible by 400 to be a leap year1600, 2000 were leap years; 1700, 1800, 1900 were not; 2100, 2200, 2300 will also not be leap years.
Every 400 years there are only 97 leap years. WHY???


The idea of the leap year started with Julius Caesar. In 46 BC, Caesar added one extra day to every fourth year to make the avarage year 365.25 days long. This was to take account for the fact that the Earth takes 365.2422 days to complete one orbit of the Sun.
But the fix wasn't exact. In 1267, Roger Bacon noticed that the calendar has slipped by nine days in the intervening 13 centuries.
After a lot of thinking, Pope Gregory XIII in 1582 adjusted the calendar (skipped 10 days – jumped from 4 to 15 October) as used today to correct for the slippage. Dates of 5th to 14th October do not exist in the Gregorian Calendar! Gregorian Calendar also skips three leap years every 400 years to make the year 365.2425 days.
This is still about 26 seconds too long!

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