农历是怎么算的？
How does the Chinese lunar calendar work?
Name: ________________ Date: ________
2025年的春节是1月29日，2026年的春节却到了2月17日，相差将近三个星期。难怪很多外国朋友会疑惑：中国人最重要的节日，为什么每年都不固定？其实，春节的日子一点儿也没变，它永远是农历的正月初一。变的，是农历和公历之间的距离。
农历的“月”，是跟着月亮走的。月亮从完全看不见，到慢慢变圆，再到重新消失，一个周期大约是二十九天半。所以，农历每个月的第一天，也就是初一，夜里几乎看不到月亮；到了十五前后，月亮最圆。中国有句俗话，叫“十五的月亮十六圆”，说的就是月亮有时要晚一天才最圆。因为周期不是整数，农历的月份，有的三十天，有的只有二十九天。
问题恰恰就出在这里。十二个这样的月加起来，大致只有三百五十四天，比地球绕太阳一圈的三百六十五天少了大约十一天。如果不管它，春节就会一年比一年早，大约十几年以后，就会变成一个夏天的节日。伊斯兰教的历法完全按照月亮计算，结果斋月有时在炎热的夏天，有时在寒冷的冬天。
为了弥补这个误差，古代的天文学家想出了一个巧妙的办法：每隔两三年，就在一年里多加一个月，叫做“闰月”。十九年里大约要加七次，有闰月的那一年，一共有十三个月。加在哪个月后面，要看二十四节气，也就是说，要看太阳的位置。所以，农历其实不是纯粹的“阴历”，而是一套同时兼顾月亮和太阳的历法。正因为这样，春节一般是冬至以后的第二个初一。在公历上，它总在1月21日到2月20日之间，有早有晚，却总是在冬天快要结束、春天快要来临的时候。
今天，中国人上班上学用公历，逢年过节却依旧看农历。很多老人也习惯过农历生日，所以他们的生日在公历上每年都不一样。下次过春节，你不妨抬头看看夜空：除夕那天晚上，天上是没有月亮的。中国人在一个看不见月亮的夜晚迎接新年，十五天以后，又在元宵节这一年的第一个圆月下，把年过完。
Key words
| Word | Pinyin | Meaning |
|---|---|---|
| 将近 | jiāngjìn | nearly; almost; close to |
| 固定 | gùdìng | fixed; regular; to fix; to fasten |
| 圆 | yuán | round; circular; circle |
| 消失 | xiāoshī | to disappear; to vanish |
| 绕 | rào | to go around; to circle |
| 计算 | jìsuàn | to calculate; to compute; calculation |
| 古代 | gǔdài | ancient times; antiquity |
| 位置 | wèizhì | position; place; location |
| 除夕 | chúxī | New Year's Eve (esp. Lunar New Year's Eve) |
| 天上 | tiānshàng | in the sky; in heaven |
| 迎接 | yíngjiē | to welcome; to meet; to greet |
| 相差 | xiāngchà | to differ; to be apart (by an amount) |
English (for the teacher)
In 2025 Spring Festival fell on 29 January, but in 2026 it came on 17 February, almost three weeks apart. No wonder many foreign friends are puzzled: why is the most important Chinese holiday on a different date every year? In fact the day of Spring Festival never changes at all: it is always the first day of the first month of the lunar calendar. What changes is the gap between the lunar calendar and the Western one.
A “month” in the lunar calendar follows the moon. From the moon being completely invisible, to slowly growing round, to disappearing again, one cycle takes about twenty-nine and a half days. So on the first day of each lunar month, the chuyi, you can hardly see the moon at night, and around the fifteenth the moon is at its roundest. There is a Chinese saying, “the moon of the fifteenth is roundest on the sixteenth”, which means the moon is sometimes a day late to be at its roundest. Because the cycle is not a whole number of days, some lunar months have thirty days and some only twenty-nine.
And that is exactly where the problem lies. Twelve of these months add up to roughly three hundred and fifty-four days, around eleven days fewer than the three hundred and sixty-five it takes the Earth to go round the sun once. If you leave it alone, Spring Festival comes earlier every year, and in a dozen or so years it would become a summer holiday. The Islamic calendar goes entirely by the moon, and as a result Ramadan sometimes falls in the heat of summer and sometimes in the cold of winter.
To make up for this error, ancient astronomers came up with a clever solution: every two or three years, add an extra month to the year, called a “leap month”. About seven are added every nineteen years, and a year with a leap month has thirteen months in all. Which month it follows depends on the twenty-four solar terms; in other words, on the position of the sun. So the Chinese calendar is not really a pure “moon calendar”, but a system that takes care of the moon and the sun at the same time. That is why Spring Festival usually falls on the second first-of-the-month after the winter solstice. On the Western calendar it always falls between 21 January and 20 February, sometimes earlier and sometimes later, but always just as winter is about to end and spring is about to arrive.
Today Chinese people use the Western calendar for work and school, but for festivals they still go by the lunar calendar. Many older people also keep their birthdays by the lunar calendar, so their birthday lands on a different Western date every year. Next Spring Festival, why not look up at the night sky: on New Year’s Eve there is no moon. Chinese people welcome the new year on a night when the moon can’t be seen, and fifteen days later, at the Lantern Festival, they finish celebrating it under the first full moon of the year.