The first day of the lunar calendar, the the Year of the Loong, is about to leave, and the Year of the Snake is approaching. On the occasion of bidding farewell to the old year and ushering in the new year, people with a mind will find an interesting phenomenon: the the Year of the Loong in Jiachen has only 354 days, while the Year of the Snake in Yisi has 384 days. The latter is 30 days longer than the former. In the same lunar year, the Year of the Snake is longer than the Year of the the Year of the Loong. Why? Where are these 30 days? The lunar calendar is a traditional Chinese calendar that takes into account the period of the moon's orbit around the earth and the period of the earth's orbit around the sun. It is a combination of yin and yang calendars. Yang Jing, a member of the Chinese Astronomical Society and a council member of the Tianjin Astronomical Society, explained that according to the Chinese lunar calendar, the day on which the lunar phase "Shuo" is located is the first day of each month, and the next "Shuo" date is the first day of the following month. The average duration of a synodic month is 29.5306 days. Due to the fact that the number of days in a month needs to be expressed as an integer, sometimes it is 29 days in a small month and 30 days in a large month. Due to the varying lengths of the 'synodic moon' itself, with a difference of nearly half a day, it may occur for several consecutive large or small months. A lunar calendar year consists of 12 months, with a length of 354 or 355 days. The current Gregorian calendar is a solar calendar, and the time interval between the sun passing through the vernal equinox twice in a row is called a tropical year, with an average length of about 365.2422 days. Due to the fact that the average length of a tropical year is not an integer, the Gregorian calendar has both regular and leap years, with 365 days in regular years and 366 days in leap years. In this way, there is a difference of about 11 days between a lunar calendar year and a year of return. If the Chinese New Year is celebrated about 11 days earlier every year, it will be celebrated in winter this year, and in a few years, it will be celebrated in summer. To avoid such "embarrassing incidents", ancient Chinese people used the method of adding leap months to make the average length of the lunar year close to the length of the tropical year. They added 7 leap months to the 19 lunar years, and the year with a leap month had 13 months, known as a leap year, which was 384 or 385 days longer. In this way, the number of days in 19 lunar years and 19 tropical years is almost equal. The specific placement of leap months in which month is related to the 24 solar terms, and leap months will be arranged in the lunar calendar when there is no solar term. The ancients divided the twenty-four solar terms into twelve solar terms and twelve qi, which were arranged alternately. The lunar calendar stipulates that every synodic month has a middle energy. If a month does not contain a middle energy, it is not a regular month and is counted as a leap month from the previous month. Yang Jing said that the upcoming Year of the the Year of the Loong in Jiachen is a normal year, with 354 days throughout the year, starting on February 10, 2024 and ending on January 28, 2025. The upcoming Year of the Snake in Yisi is a leap year, with a "leap June" of 384 days, starting on January 29, 2015 and ending on February 16, 2026. The Lunar New Year is approaching, auspicious snakes bring blessings, and the new year begins. May everyone have their wishes and hopes in the new year. (New Society)