Explaining why after the Lunar New Year of Giap Thin, there will be another 30th day of Tet in 8 years

According to the Perpetual Calendar, 2024 has December 30, which is December 30th of the lunar calendar. However, it will not be until 2033 that December 30th (Lunar New Year's Eve) will come around again, and from 2025-2032 December will only have 29 days.

Decorative accessories for Tet 2024 with the wish "Everything goes as you wish" on Hang Ma street. Illustration photo: Hoang Hieu/VNA

That means after 2024, it will be another 8 years before there is another 30th of Tet.

Explaining this phenomenon, expert Tran Tien Binh, author of the book Vietnamese Calendar of the 20th and 21st centuries, analyzed that the first day of the lunar month is the day when the Earth-Moon-Sun are in a straight line, the Moon turns its dark side towards the Earth. This day is also called the No Moon day (or Soc day); when calculating, the Soc point falls at any time of the day from 0:00 to 24:00, that day is the first day of the lunar month. The lunar month is the length of the distance between 2 Soc days, rounded to 29 days (short month) and 30 days (full month).

This is because the length of a lunar month varies from 29.27 days to 29.84 days; the average is 29.53 days.

Expert Tran Tien Binh gave a typical example: In 1968, Vietnam started using the calendar based on the 7th time zone, so Vietnam celebrated Tet 1 day before China. The reason is that December 31, 1967 corresponds to the 1st day of the 12th lunar month in both the Vietnamese and Chinese calendars, but the next Soc point occurs at 23:29 Vietnam time on January 29, 1968, so December in the Vietnamese calendar only has 29 days (short month), at this time according to Beijing time it is 0:29 on January 30 (full month). Therefore, the 1st day of Tet Mau Than 1968 in Vietnam is 1 day earlier than in China.

According to expert Tran Tien Binh, calculating the movement of celestial bodies is very complicated, especially for the Moon due to the influence of gravitational disturbances from the Sun, Earth, other planets and the irregular shape of the Earth's sphere as well as the Moon.

"Therefore, it is meaningless to count the full and short Decembers in each year, but it all depends on the exact calculation at each specific time. For example, the years 2014, 2015, 2017, 2018, 2019, 2020, 2021 have full Decembers (30 days), but in 2022 there will be a short December (29 days), and in 2023 and 2024 there will be full Decembers again. Then there will continue to be short Decembers until 2033 when there will be a full December again," expert Tran Tien Binh emphasized.

According to Baotintuc.vn

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