Leap Year

A leap year has 366 days. It is also known as an intercalary year or bissextile year. It occurs every 4 years.

In the Gregorian calendar, which is used worldwide, the extra day is added to the shortest month of the year which is February. Hence, February has 29 days instead of 28 days. The 29th day, in February, is called the leap day or intercalary day.

Why do we have a leap year?

In the Gregorian calendar, the common year is 365 days.

The Earth takes 365.242189 days (365 days, 5 hours, 48 minutes, and 46 seconds) to make a complete revolution around the sun.

Hence, there is a need to add the extra 0.242375 days.

Therefore, every 4 years an extra day is added which brings an average of 365.25 days per year, but it is not accurate.

To fix the problem, in centuries divisible by 400, an extra day is added which brings an average of 365.2425 days per year, though not perfect but fairly close.

Hence, a leap year is necessary to keep the calendar aligned with Earth’s revolution around the sun.


Origin of leap year

The Origin Of Leap Year

In 45 B.C. Julius Caesar introduced the Julian calendar.

In the Julian calendar every 4th year, a day was added to the calendar to align with the solar year.

By 1582, the vernal equinox (beginning of spring) was ten days early. Hence, Pope Gregory XII called upon astronomers for a solution.

Astronomers found out that miscalculations during the past 15 centuries have resulted in the fact that there is a 10-day difference between the calendar year and the solar year.

Hence, that year they removed ten days from the calendar. The day after 4th October 1582 was 15th October 1582. This skipping of 10 days brought the calendar into agreement with the solar year.

The new calendar was more accurate than the Julian calendar. It was named the Gregorian calendar in honor of Pope Gregory XII.

In the Gregorian calendar, to keep the calendar and the solar year in agreement, the leap year was omitted 3 times every 400 years. This was done by not counting as leap years the years ending in 2 zeroes unless they can be divided by 400.


How to calculate a leap year

To know whether it is a leap year the following criteria are taken into account. They are:

For non-century years, it is a leap year, if it can be evenly divided by 4.

For example 2008, 2012, 2016 are leap years.

For century years (A century year is a year ending in 00) it is a leap year if it can be evenly divided by 400.

For example 1900, 2100, 2200, 2300 are not leap years.

For example 1600, 2000, 2400, 2800 are leap years.


List of leap years 1800-2400

1804
1808
1812
1816
1820
1824
1828
1832
1836
1840
1844
1848
1852
1856
1860
1864
1868
1872
1876
1880
1884
1888
1892
1896
1904
1908
1912
1916
1920
1924
1928
1932
1936
1940
1944
1948
1952
1956
1960
1964
1968
1972
1976
1980
1984
1988
1992
1996
2000
2004
2008
2012
2016
2020
2024
2028
2032
2036
2040
2044
2048
2052
2056
2060
2064
2068
2072
2076
2080
2084
2088
2092
2096
2104
2108
2112
2116
2120
2124
2128
2132
2136
2140
2144
2148
2152
2156
2160
2164
2168
2172
2176
2180
2184
2188
2192
2196
2204
2208
2212
2216
2220
2224
2228
2232
2236
2240
2244
2248
2252
2256
2260
2264
2268
2272
2276
2280
2284
2288
2292
2296
2304
2308
2312
2316
2320
2324
2328
2332
2336
2340
2344
2348
2352
2356
2360
2364
2368
2372
2376
2380
2384
2388
2392
2396
2400

How many days does the leap year have?

A usual calendar has 365 days whereas the leap year has 366 days.


Classic leap year rhyme

Thirty days hath September,
April, June, and November;
All the rest have thirty-one,
Excepting February alone,
And that has twenty-eight days clear,
And twenty-nine in each leap year.
- MOTHER GOOSE

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