今年有两个二月份？原来“闰月”是这么来的……

民间广为流传一种说法：“三年一闰，五年两闰，十九年七闰。”

老一辈常说2023癸卯兔年是个好兆年、吉祥年，“双春兼闰二月”，也就是在农历二月过后还有一个二月。

这种现象是怎么发生的呢？

Most people should have heard of the term "double spring and leap month" and said it's a sign of good fortune and great for loved ones to get married. But what exactly is that?

图源：新华社

闰月（leap month）是阴阳历中为使历年平均长度接近回归年而增设的月。要想搞清楚闰月的来历，首先要明白阴历、阳历、农历都是什么概念。

阴历（lunar calendar）以月球绕地球运转一周的时间为一个月，是以月亮的盈亏（即朔望变化）而制定的，一个朔望月（synodic month）的长度是29.5306天，全年12个月就总共有354.3672天。

The moon takes about 29.5 days to revolve around the Earth, so the lunar month is sometimes 29 days, sometimes 30 days. From that, a year is about 354 days.

而阳历（solar calendar）以地球绕太阳运转一周的时间为一年，一个回归年（tropical year）的长度是365.2422天，比阴历一年多将近11天。这样的话，每经过17年，阴阳历日期就会同季节发生倒置。

But we all know a year is about 365 days and the Earth returns to its original position. There is a difference of 11 days between the lunar and solar year and about a month over 3 years.

我国采用的农历（Chinese calendar）并不是像大多数人所认为的直接等同于阴历，而是一种阴阳合历。

农历是以阴历为基础兼顾回归年制定的，它的日期既能显示月亮的盈亏变化，又能与阳历的四季保持同步。它以月球平均绕地球转一周的时间为一月。通过设置闰月，一年的平均天数就能够与地球平均绕太阳转一周的时间相等。

Many people think that the Chinese calendar is one based on the movement of the moon but this is only half correct. The Chinese calendar uses the movement of the moon around the Earth to determine the length of a month, but it also makes reference to the position of the Earth relative to the Sun to mark the year.

故而，我们的祖先在天文观测的基础上，找出了置闰的办法，弥补阴历和农历间相差的11天，以保证每个农历年的正月到三月为春季，四月到六月为夏季，七月到九月为秋季，十月到十二月为冬季。

The setting of leap month is a way to fill the gap of days between the solar calendar and lunar calendar in one year, which is 11 or 12 days, so as to make sure the four seasons basically fit the months.

In accordance with the traditional Chinese calendar, the first three months of the year should be spring, the next three should be summer, then autumn and the last three months should be winter.

为保证每月的头一天（初一）必须是朔日，也就是阴历第一天，需要经过严格的观测和计算才能确定多长时间增加一个闰月。

我国古人经过漫长时间的研究，想出了出一个求回归年日数与朔望月的日数的最小公倍数的办法，最终得出“十九年七闰法”（三年闰一个月，五年闰二个月，十九年闰七个月）。

最小公倍数：m个回归年的天数与n个朔望月的天数相等

具体闰月安排在哪个月不是随便能决定的，而是取决于我国的二十四节气。

我们的二十四节气可以继续细分为十二个节气和十二个中气，一一相间。古代历法以太阳历二十四气配阴历十二月，阴历每月二气：在月初的叫节气（minor solar terms），在月中以后的叫中气（major solar terms）。

The 24 solar terms is a gross name of the system that comprises 12 major solar terms and 12 minor solar terms interlaced with each other.

农历规定每个月都要有一个中气。某个月如果不包含中气，就算做是上一月的闰月，这就是置闰。每19个回归年中有228个中气和235个朔望月，即有7个月没有中气，这些没有中气的月便正好成为闰月。

Each lunar month in the Agricultural Calendar contains a major solar term. A lunar month that does not include a major solar term is taken as the leap month of the preceding month. In 19 tropical years there will be 228 major solar terms and 235 synodic months. So 7 lunar months will not contain major solar terms and they are classified as leap months.

今年（农历癸卯年）的闰二月就是如此。公历3月22日到4月19日，中间只有一个节气——清明，中气——谷雨则到了下一个月初一，故而这个月被称为闰二月。

图源：新华社

但是闰二月出现频率是非常少的，一般间隔19年一次，比如1985、2004、2023年等，老话“十年难逢闰二月”也是由此而来。

民间关于闰二月的俗语有很多，比如“双春闰二月，春寒逢秋旱”等。各地还有不同的习俗，以期有健康的身体，福寿延年。

❶ 送闰月鞋（buy shoes for parents）

在我国不少地方，人们认为有闰月的年份为多事之秋，于长者不利。出嫁的女儿要给父母送双闰月鞋以逢凶化吉，祝愿他们健康长寿，也就是俗话中所说的“闰月鞋，闰月穿，闰月老人活一千。”

In some places, people have the tradition of buying shoes for their parents to reward their father and mother's efforts of bringing them up, and pray for the health and safety of their parents.

图源：SIPA

❷ 喝闰月茶（drink tea）

在武夷山地区，闰月有喝茶的习俗。只有女性才有资格入席茶宴。农家妇女轮流做东邀请近村的女客入席喝茶聊天，以增进邻里和睦。

People living near Wuyi Mountain in East China's Fujian province have the tradition of drinking tea at leap month, and only women are eligible to participate. Women in the village take turns holding the tea banquet, and they drink tea while chatting, creating an harmonious atmosphere among neighbors.

图源：微博@大理文旅发布厅

❸送猪脚和面线（give mother pig feet and thin noodles）

在中国台湾某些地区，每逢闰月，嫁出去的女儿需要买猪脚和面线带回娘家送给母亲。古时候人们认为“父母逢闰年而减寿”，而猪脚面线象征着吉祥、长寿、平安。

In Southeast China's Taiwan province, leap month has such traditions as well. The married daughter has to buy pig feet and thin noodles for her mother, usually two front pig's feet and six bunches of thin noodles, and the noodles have to be tied with red silk threads and spring flowers.

❹吃闰月饭（eat dinner together）

闰月饭也叫六亲饭。每逢闰年闰月，娘家就会把已经出嫁的女儿请回家中相聚就餐。不过，在客家传统民俗文化中，闰月饭指的是在闰月时，出嫁的女儿给母亲送去的饭。

Just like other festivals, a reunion dinner is indispensable among the traditions of the leap month. When leap month comes, parents will invite the married daughter to return home and have dinner together, cherishing a wish for happiness and good fortune.

图源：新华社

所以，闰月脱胎于农业生活的需要，反映了古人阴阳调和的智慧。设置闰月的目的就是为了“正时”，确保季节、气候特点更好地服务农时。你的家乡对于“闰月”有哪些说法和习俗呢？一起来分享一下吧！

编辑：陈月华

实习生：王雨凡

来源：新华社 中国日报 惠农网 香港天文台 香港太空馆