What happened on 29th February 1900? Well nothing
since the day never existed. Now I can hear you say hang on don’t we have a
leap year every four years? And if the year in question is divisible by 4 then
it should be a leap year? The answer is partially correct.
Let us first understand why and how a leap year is
calculated. We all know that it takes 365 days, 5 hours, 49 minutes and 12 seconds
for our earth to revolve the sun. We round off the minutes and seconds and we
calculate it as 365 days and 6 hours. So six hours accumulated for four years
becomes a day and so a day is added for every four years to the month of
February which is known as leap day and the year as a leap year.
To round off the hour to a whole number i.e. to 6 hours we
add 10 minutes and 48 seconds every year. Over a period of 400 years these
extra minutes and seconds adds up to 3 days. Which means we add 648 seconds
every year, in 400 years it would become 2,59,200 seconds. Which is 3 days
(259200/60/60/24=3). To compensate these 3 days, it was decided that century
years or the years which are divisible by 100 will not be a leap year unless it
is also divisible by 400.
Therefore 1900 is not a leap year, so are 2100, 2200, 2300. Whereas
years 2000, 2400 are leap years.
Now you may want to quickly check this, I can see you opening an MS Excel file and typing 29-Feb-1900. Surprise MS Excel accepts it as a date. But try 29-Feb-2100 or 2200 etc., you will find that they are treated as a text and not as date. The reason behind the treatment of 1900 as a leap year is given in these two links by Microsoft - http://support.microsoft.com/kb/21401 and http://support.microsoft.com/kb/214058.
With Best regards,
bjayakar
