Two clocks in one calendar
Most traditional festivals in China are tied to a calendar that keeps track of two things at once: the phases of the moon and the position of the sun. Calendars that do this are called lunisolar. The months follow the moon, so each one begins on the day of the new moon and the full moon falls near the middle. The year, however, is meant to stay in step with the seasons, which are governed by the sun.
This is why the dates of the Spring Festival, the Mid-Autumn Festival and others shift on a Gregorian calendar, even though they are fixed in the traditional one. The Gregorian calendar used for civil and business life in most of the world today is a purely solar calendar. The traditional calendar is often still called the lunar calendar in everyday speech, or the farming calendar, though neither name captures the solar half of it.
How the months work
A lunar month, from one new moon to the next, lasts a little under thirty days (about twenty-nine and a half). Traditional months therefore have either twenty-nine or thirty days. Twelve of them add up to roughly 354 days, which is about eleven days shorter than a solar year of roughly 365 days.
Months are usually named by number: the first month, the second month and so on. The first day of a month is the new moon, and the fifteenth day is close to the full moon. That is why so many festivals fall on the fifteenth: the Lantern Festival on the fifteenth of the first month and the Mid-Autumn Festival on the fifteenth of the eighth month both celebrate a bright full moon.
Keeping the year in step with the seasons
If twelve lunar months were simply repeated, the calendar would drift about eleven days earlier against the seasons each year. After a few years, a spring festival would land in winter. To prevent this, the traditional calendar inserts an extra month from time to time, called a leap month. Over a long stretch, this happens roughly seven times every nineteen years, so a leap year of thirteen months appears about every two to three years.
The rule for deciding where to put the leap month depends on the sun. The calendar uses a set of solar divisions, described in more detail in the article on the solar terms, and a month that does not contain one of the principal ones is the candidate for being repeated. The leap month takes the same number as the month before it, so a year might have two consecutive months both numbered, for example, the fourth.
Because of leap months, the traditional New Year can fall anywhere from roughly late January to about the middle of February in the Gregorian calendar. Other festivals shift within a similar window of a few weeks.
Solar terms and the farming year
The solar half of the system is a division of the year into twenty-four periods of roughly fifteen days each, based on the sun’s apparent path. These mark the start of spring, summer, fall and winter, the equinoxes and solstices, and many in-between points with names about rain, insects, dew and frost. Because they follow the sun, they fall on nearly the same Gregorian dates every year, usually within a day or so.
For farmers, this was the practical part of the calendar. The lunar dates told you the phase of the moon, but the solar terms told you what the weather and fields were likely to be doing. Two of the year’s best-known occasions are actually solar terms rather than lunar dates: Qingming in early spring and the Winter Solstice in midwinter. Their dates do not wander the way lunar festivals do.
Where the major festivals fall
The traditional festivals can be arranged in order around the year.
- First month, first day: the New Year, covered in depth in the piece on the Chinese New Year.
- First month, fifteenth day: the Lantern Festival, which closes the New Year season.
- Early April (a solar term): Qingming, the spring day for remembering ancestors.
- Fifth month, fifth day: the Dragon Boat Festival.
- Seventh month, seventh day: Qixi, based on a love legend.
- Eighth month, fifteenth day: the Mid-Autumn Festival.
- Ninth month, ninth day: the Double Ninth Festival.
- Around December 21 or 22 (a solar term): the Winter Solstice.
- Twelfth month, eighth day: Laba, which begins the final countdown to the New Year.
Notice how the dates often repeat the same number: the fifth day of the fifth month, the seventh of the seventh, the ninth of the ninth. In traditional thinking, odd numbers were associated with the yang side of yin and yang, so a doubled odd number was considered especially charged with meaning.
Years, cycles and the zodiac
The calendar also counts years in cycles. Two sets of symbols, ten Heavenly Stems and twelve Earthly Branches, are combined in turn to produce a cycle of sixty years. Each of the twelve branches is paired with an animal, which gives the Chinese zodiac. Someone said to be born in a year of a certain animal is really identifying their position in a twelve-year sub-cycle. The animal year changes at the traditional New Year, not on January 1, which is why people born in January or early February sometimes belong to the previous animal.
A calendar with a long history
Calendar-making in China goes back to very early times, and observing the sky was a serious state duty. Rulers were expected to issue a correct calendar, and an accurate one was part of the proof that a dynasty governed well, a theme connected to the Mandate of Heaven. Over the centuries, astronomers refined the methods for predicting new moons and solar terms, and different dynasties adopted reformed calendars. A reform during the Han dynasty is commonly remembered as an important step in fixing the basic arrangement that later calendars built on, though the details of each reform are a topic for specialists.
Living with two calendars
Today, ordinary life in China and in Chinese communities abroad runs on the Gregorian calendar for work, school and official dates. The traditional calendar remains in use for festivals, family occasions and, for many people, choosing auspicious days for weddings or openings. Practices differ from household to household and from place to place, and some people follow the old calendar closely while others barely notice it outside the major holidays.
Understanding the lunisolar structure makes the whole festival cycle easier to follow: the moon sets the rhythm of the months, the sun anchors the seasons, and the festivals sit where the two meet.