Why 100th year is not considered as leap year in every 100 years?

Question

Leap Year calculation concept

Answer 1

The earth takes 365.24 days to take one revolution about sun. So after 4 year a correction of 1 day is taken for extra 0.98 day. And to correct an error of 0.02 day 100th year is not taken as leap year.

Answer 2

Because a year is not exactly 365.25 days long. It is more like 365.24 days long. So by adding a full day every 4 years we build up a small error. After a a Century that error is a full day long, so we skip the leap year. This is easy to understand when you realize the difference between 365.25 and 365.24 is 1/100 of a day per year. So after 100 years we have accumulated a full day of error.



But guess what. A year is not exactly 365.24 days. It is more like 365.2424 days.

So that extra 24/1000 means that correcting a full day every 100 years builds up an error in the other direction about every 400 years. So once every 400 years we put the century leap day back in. It takes about 8000 years for that correction to accumulate a day of error, so we are good for a while.



But all this calculating is an attempted to make a year come out to an even number of days. The orbit around the sun and the spin on the earths axis just don't synch up to our convenience - they are what they are. So, calendars that are based on the solstice, where the old year ends and the new year begins on the day of the solstice are never off. The Mayan calendar works this way.

Answer 3

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The calender is so designed that it repeats itself after 400 years. For example see this: Say the first day of the year 2001 is a Monday. Every year there are 365 days i.e. 52 weeks and 1 odd day. (That makes 1 jan 2002 a tuesday) For a leap year it is 366 days i.e. 2 odd days. Any year is considered to be a leap year if it is divisible by 4. But if the year is divisible by 100 then it should be divisible by 400. So 2001-2100 contains 24 leap years(2100 is not a leap year) and 76 ordinary years making it 76*1+24*2 = 124/7 = 5 odd days Similarly for 2100-2200 and 2200-2300 also contain 5 odd days each. But 2300 to 2400 contains 25 leap years as 2400 is a leap year So the number of odd days is 75+ 25*2= 150 /7 = 6 odd days Therefore number of odd days for the whole of 400 years is 5+5+5+6 = 21/7 = 0 odd days Again making Jan 1 2401 a monday.

Answer 4

Not precisely true:



Years that are evenly divisible by 100 are not leap years, <> they are also evenly divisible by 400, in which case they are leap years. For example, 1600 and 2000 were leap years, but 1700, 1800 and 1900 were not. Similarly, 2100, 2200, 2300, 2500, 2600, 2700, 2900 and 3000 will not be leap years, but 2400 and 2800 will be.



The solar year is not exactly 365 1/4 days long. It is a tiny bit less, so once in a while, you need to omit a leap year. Even this scheme is not exactly accurate, as we will eventually be about a whole day off in about 8,000 years.

Answer 5

Because of the length of the year. If every full century were a leap year, the average year would be a bit too long, therefore only the centuries divisible by 400 are leap years. That still doen't give a totally exact value but is a better approximation.

Answer 6

The earth takes 365.24 days to take one revolution about sun. So after 4 year a correction of 1 day is taken for extra 0.96 day. Because of that an error of 0.04 creeps in the calculation.so after 100 years that error becomes equivalent to 1day. so again the error is nullified by not considering the 100 year as a leap year(not adding a day).

Calculations: the error of .04 comes in every 4 years. so in 100 years there will be 100/4=25 times error introduced....so total error in 100 years is 25*0.04=1.00day....hence the correction.

Answer 7

Gregorian calendar have leap years every four years, have century leap year correction too. AD 2000 was leap year, AD 2100, 2200, 2300 not leap years however, 2400 is next century leap year. 2500, 2600, 2700 not leap years, 2800 is leap year. Reason of this is solar years is odd number, is 365 days, 5 hours, 48 minutes about 46 seconds. That is 365.2422 days, not quite 365.25 days, thus one extra day every four years is a bit excessive, thus eliminate leap years at centuries not evenly divisible of 400.

Answer 8

coz leap year is defined as the year with an extra day not an year with 25 extra days or an extra month lol

probably u could set a new trend !!! :) lol

also every 4 years there is a total of 365x4 +1 days worth of time spent so they mark it as soon as the extra day is completed rather than waiting for 24 more days to complete.

Answer 9

because the correction is needed every four years



waiting for the century mark - would make 25 days to correct



and throw a BUNCH of annual calculations WAY off

like planting - harvest - etc



good question

Answer 10

Because leap year is every four years.