During the recent Chinese New Year celebrations, the media – including the Post – frequently used the term “Lunar New Year”.
This description is not strictly correct. The Chinese calendar is not a lunar calendar like the Islamic calendar, but a mixed solar/lunar calendar. The date of the Chinese New Year is linked to both the sun and the moon.
Of course, every month of the Chinese calendar begins at new moon, and the dates of the Chinese month track the phase of the moon. A lunar month is based on the phase cycle of the moon, which has either 29 or 30 days.
But a year in the Chinese calendar follows the period of the sun, which has approximately 365 and a quarter days. Twelve months therefore fall well short of a year. In order to match the solar and lunar cycles, intercalary months have to be added from time to time.
The Chinese calendar is also sometimes called an agricultural calendar because farmers rely on an accurate calendar to plough, seed and harvest at the right time. Agricultural activities depend on the seasons, which are controlled by the sun.
The solar aspect of the Chinese calendar consists of 24 seasonal markers. Among these are markers of the four seasons: the vernal equinox, summer solstice, autumnal equinox and winter solstice.
Since a year in the Chinese calendar can have 12 or 13 months, it is unclear when the new year should begin. The winter solstice is the most important festival for farmers. Starting from this date, they have to stock up food and try to survive the difficult coming months.
In the Chinese calendar, winter solstice (a date set by the position of the sun) always occurs during Month 11, and the new year is assigned to the second new moon after the winter solstice.
For example, the winter solstice for 2016 was on December 21, which corresponds to the 23rd day of the 11th lunar month. The next new moon was on December 29, and the one after that was on January 28, the first day of the Chinese New Year.
The farmers rely on the 24 seasonal markers to guide their work in the field. In the old calendar, devised during the Yuan dynasty by astronomer Guo Shoujing (郭守敬), the seasonal markers were separated by an equal number of days.
However, the sun does not move with uniform speed along its path (the ecliptic) throughout the year, and the seasonal marker corresponding to the summer solstice always fell behind the date of the true summer solstice. These errors were not beneficial to the farmers.
With the introduction of Western astronomical knowledge, efforts to reform the calendar began as far back as the late Ming dynasty.
In 1645, the Jesuit priest Johann Adam Schall von Bell designed a new calendar, in which the seasonal markers were based on the sun’s actual position on the ecliptic and were no longer separated by equal time intervals. These changes resulted in a much more accurate calendar for the farmers.
The court astronomer Yang Guang Xian (楊光先) opposed this new calendar and famously said: “I would rather China not have a good calendar than have Westerners in China.”
The Emperor Kangxi (康熙 ) finally adopted the new calendar in 1670, and it remains in use today.
We should note that other Asian countries such as Korea and Vietnam also celebrate the New Year at this time, so maybe the term “Chinese New Year” is a bit chauvinistic. However, since these other countries inherited their calendars from the Chinese, the term is not unreasonable.
Until someone can suggest a better name, I will continue to call it Chinese New Year – but certainly not Lunar New Year.
Sun Kwok is chair professor of space science at the University of Hong Kong and the president of the Astrobiology Commission of the International Astronomical Union. The history of calendar reforms is one of the many topics covered in his upcoming book Our Place in the Universe