二月份就要结束了，今年2021年是平年，因此二月份有28天。那么小伙伴们知道如何计算哪年是平年，哪年是闰年吗？公历年份是4的倍数的，一般都是闰百年。但公历年份是整百数的，必须是400的倍数才是闰年。按照这样的口诀就好记了：四年一闰，百年不闰，四百年再闰。 例如：2000年是闰年，2100年则是平年。
那么为什么是这样的呢？今天我们一起来学习一下吧？
Many centuries back, a Roman King called Numa made a calendar according to 12 lunar cycles which approximately take 354 days.
许多世纪以前，一位名叫努玛的罗马国王根据12个农历周期制作了一个日历，周期大约为354天。
But as even numbers were considered unlucky, Numa rounded off days to 355.
但是偶数被认为是不吉利的。
He also made each month odd-numbered, leaving one month. That is Februaries with 28 days to reach the total of 355.
他又把每个月都编为单数天数，这样剩下了一个月，就是二月有28天，总共355天。
But as the earth takes 365.24 days to travel around the sun. Seasons and weather conditions started mismatching with the 355-day calendar.
但是地球绕太阳运行需要365.24天。季节和天气开始与355天的日历出现了不匹配的现象。
Then came Julius Caesar who decided to follow the solar calendar of the Egyptians that had Januaries and Februaries in the beginning.
后来凯撒大帝决定遵循埃及人的阳历，一月份和二月份在日历的最开始。
He made the calendar into 365 days by adding days in each month except February.
除了二月份以外，他在每个月份都加了几天，日历总体天数达到365天。
As still 0.24 days were pending each year, after every 4 years, he added 1 day to February. Making it a leap year. Thus, February has 28 days except during leap year.
因为每年仍然多出0.24天，每四年，他在二月份增加了一天。使之成为闰年。因此除了闰年，二月份有28天。
生词
even numbers n.偶数
rounded off v.四舍五入
odd-numbered a.奇数的
mismatch with v.使不匹配
pending a. 待定的
leap year n.闰年
