Why Does It Take 8 Years for the Lunar Calendar to Catch Up and Have a 30th Day of the Month Again in 2033?

26 January, 2025

Why won’t there be a 30th day of the Lunar New Year from 2025 to 2032?

The Lunar New Year follows the lunar calendar, which is based on variable factors that are difficult to determine, unlike the solar calendar. The length of each lunar month depends on actual observations rather than predetermined rules. Therefore, the lunar calendar depends on factors that are not standardized and challenging to predict, but they are also essential for ensuring the accuracy of the lunar calendar. Lunar months are calculated according to the changing phases of the moon, from the new moon to the crescent, quarter, gibbous, and full moon, and then back again.

Eight consecutive years without a 30th day of the Lunar New Year

A lunar month starts from the new moon, when the moon is on the same side as the sun, known as the “dark moon” or “conjunction.” The day this occurs is considered the first day of the lunar month. The length of time between two consecutive dark moons varies from month to month. This variation is caused by the elliptical shape of the Earth’s orbit around the sun and the moon’s orbit around the Earth, which results in uneven speeds as they travel across the sky, affecting the monthly interval between their alignments (known as syzygy).

As a result, the average length of a lunar month is 29 days, 12 hours, 44 minutes, with deviations of up to 7 hours. This can lead to variations in the length of a lunar month, resulting in either 29 or 30 days. According to these calculations, the next time the 30th day of the Lunar New Year will occur is on January 31, 2033.

Why can’t the lunar calendar be calculated as precisely as the solar calendar?

The lunar month depends on the length of the lunar cycle and the dark moon, which change every month due to various factors. Therefore, it is impossible to establish a fixed rule, and each month must be calculated accurately based on observations. The upcoming eight consecutive years without a 30th day of the Lunar New Year is a coincidence and does not represent a pattern in the calendar system. Moreover, the lunar calendar has been used in Vietnam for a long time, and this phenomenon is not unusual. For example, from the year of the Monkey (2016) to the year of the Rat (2020), there were five consecutive years with a 30th day of the Lunar New Year in the last month.

The year 2025, the Year of the Snake, will not have a 30th day of the Lunar New Year but will have two “Beginning of Spring” festivals

The year 2025, the Year of the Snake, will have an intercalary sixth month, resulting in two “Beginning of Spring” festivals, one at the beginning of the year and another towards the end. This is also a coincidence.

In folk spirituality, it is believed that a year with two “Beginning of Spring” festivals brings good luck, prosperity, and renewed blessings.

The Year of the Snake 2025 will have two “Beginning of Spring” festivals

However, the absence of a 30th day of the Lunar New Year in the Year of the Snake 2025, known as a “missing month,” raises the question of whether it will affect the year’s luck.

*Reference for divination