Why does New Year’s Eve “disappear” but New Year’s Day is never “absent”?

If you open the calendar, you will find that 2024 is the last year with New Year's Eve in the next few years. There will be no New Year's Eve in the five years from 2025 to 2029. After the twenty-ninth day of the lunar year, it will be the first day of the lunar year. Where did New Year's Eve go? Why does New Year's Eve sometimes "disappear" but never "absent" on the first day of the lunar year? Astronomy popular science experts can help you solve your doubts.

"This situation is related to the Chinese lunar calendar. In the Chinese lunar calendar, the lunar month is mainly based on the cycle of the moon's waxing and waning." Wang Kechao, director of science popularization at the Purple Mountain Observatory of the Chinese Academy of Sciences, said that during the moon's rotation around the earth, the moon presents different appearances when viewed from the earth. When the geocentric ecliptic longitude of the moon and the sun is equal, the moon is not visible on the earth. The moon phase at this moment is called the new moon, and the day is called the new moon day. It is the first day of each lunar month and is called the first day of the lunar calendar. Therefore, the first day of the lunar month appears in every lunar month.

Wang Kechao introduced that the interval from one new moon to the next is a lunar month, which is called a synodic month, and the average length is 29.53 days. In fact, the length of a synodic month is not fixed, and it is more than 29 days. The shortest in this century is 29.27 days, and the longest is 29.82 days. Rounding up, the lunar month is divided into a long month and a short month, the former is 30 days, and the latter is 29 days. If the twelfth lunar month happens to be a short lunar month, New Year's Eve will be "absent".

The arrangement of lunar months depends on the actual moon phases, and the arrangement of big and small months is different from that of the Gregorian calendar. Generally speaking, the proportion of the two being arranged at intervals is higher, and sometimes there are two consecutive big months or two consecutive small months. "According to long-term statistics, the proportion of having New Year's Eve is slightly higher. It is normal to have no New Year's Eve for five consecutive years, but it is relatively rare." Wang Kechao said.

"The Gregorian calendar is based on the movement period of the Earth's revolution around the sun, and the lunar calendar is based on the cycle of the moon's phases. The lunar calendar, which has been used in my country since ancient times, takes into account the cycle of the moon's phases and the length of the tropical year. It is a combined solar and lunar calendar that demonstrates the superb wisdom of the ancients," said Wang Kechao.

Regardless of whether it is the 29th or 30th day of the lunar year, New Year's Eve, which is connected with the beginning of the new year, is always there. People gather with their families on New Year's Eve to bid farewell to the old year and welcome the new spring, welcoming a brand new good year together.

Planning: Liu Xinhui

Reporter: Wang Jueyin, Qiu Bingqing

Poster: Li Yinru

Editors: Zhu Shun, He Xiao

Produced jointly by Xinhua News Agency Domestic Department and Xinhua News Agency Jiangsu Branch

Produced by Star Studio