Leap Years

		If you can remember back to what you were taught in school ... A leap year is a year where the number of that year can be divided by four without leaving any remainder However, that is not the whole truth of the matter. How leap years work Every year ( ignoring leap years for the time being ) is nominally 365 days long. That means it takes 365 days for the Earth to orbit around the Sun and get back to where it started from. Unfortunately it takes about 365.25 days to complete an orbit so every 365 days we are a litle further back than where we were that year ago. If this situation was allowed to continue unchecked, after some 750 years, what is now the middle of summer would be the middle of winter and vice versa. To correct this defect we add an extra day to our year every four years; that is a leap year. Whilst our leap year every four years, conveniently defined as being in every year that is divisible by four without leaving a remainder, generally corrects the problem the oribit is not exactly 365.25 days thus it requires a further correction. This correction is provided every 100 years when a leap year does not occur and, further still, every four of those 100 years when a leap year does indeed occur. This means that simply dividing the number of the year by four and checking there is no remainder is not a correct way of determining if a year is a leap year or not The full leap year rules The full rules for calculating whether a year is a leap year or not are - If the year is before 1601 AD then; if the number of the year can be divided by four without leaving any remainder, it is a leap year and, if it can't, then it isn't a leap year otherwise, for years after 1600 AD If the number of the year can be divided by 400 without leaving any remainder; it is a leap year otherwise If the number of the year can be divided by 100 without leaving any remainder; it is not a leap year otherwise If the number of the year can be divided by four without leaving any remainder; it is a leap year otherwise It is not a leap year Failure to know or understand these complete rules are one aspect of the Millennium Bug that is predicted to occur in some computer software in the year 2000 AD. Because 2000 AD is exactly divisible by 400 it is a leap year. If only the basic divide by four rule is used then, luckily, the year will be treated correctly as a leap year. The problem arises when someone has knowledge of the divide by 100 rule but not of the divide by 400 rule; in these cases 2000 AD will not be treated as a leap year which is incorrect. Were you taught the full leap year rules ? Have the complete leap year rules come as a total surprise, or are they something that you were taught at school ? If you were taught them you are, as far as I can tell, one of the lucky few. Everyone else, myself included, appears to have been fed the divide by four rule as if it were an absolute and complete system for determining when leap years occur. I was quite surprised when I discovered, quite a while ago now, that I had not been told the full truth and, believing that what I was taught was more correct, even had to check the matter in an encylopedia before I could accept that what I had been taught was simply incorrect or, at least, misleading. Now, if your educators have misled you, like they did me, on something that is a fundamental fact of life and nature, then what else have you been told or taught that may not exactly be fact, especially where subjects of a more political or jingoistic nature are involved ? Did all the co-operatives in communist Russia really only have a couple of tractor's that they shared amongst themselves ? Were the Spanish Inquisition the most evil force known to man ? Was colonialisation the best thing for those under the Empires control ? If it's always, I before E, except after C, why are there weird, and not so weird, words that don't conform to this rule ? Did anyone ever mention leap seconds ?
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First published sometime before Tuesday the 11th of January, 2000 Last upload was on Tuesday the 23rd of September, 2003 at 19:20:19