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The “24 solar terms” is a collective name of the system that comprises 12 “major solar terms” and 12 “minor
solar terms”. Their names are listed in the table attached. “Vernal equinox” is the rst “major solar term”,
followed by the rest of the minor and major solar terms alternating with each other, with the cycle ending at
“insects waken”.

History of Chinese Calendaristory of Chinese Calendar
H

A complete set of “24 solar terms” rst appeared in an ancient book “Huainan Zi” in early Han Dynasty in
which a chapter gave a concise description about astronomy and phenology. These 24 solar terms were soon
absorbed into “Tai Chu Li”, the rst well documented calendar in the history of China. At that time, the “24
solar terms” began at “winter solstice”, and evenly marked on the “ecliptic” with a constant time interval of
about 15 days.

Towards the end of the Ming Dynasty, traditional astronomy, mathematics and calendar were ameliorated
with the use of western science and technology. In the early Qing Dynasty, when the authoritative
organization for compiling the calendar was under the charge of the Jesuits, a major reform of the calendar
was conducted. The o cial calendar “Shi Xian Li” was published in 1645 and the “vernal equinox” was adopted
as the rst solar term. Positions of all the “24 solar terms” were xed at pre-de ned longitudes in an “ecliptic”
coordinate with a constant angular separation of 15 degrees, corresponding to a period of 14.71 to 15.74
[1]
days . Such a practice is still in use today.

The Chinese Agriculture Calendar is a combination of the lunar and solar calendar systems. There are
365.2422 days in one “sidereal year” while 12 lunar months add up to 354 days. To harmonize the lunar and
solar calendars, a leap lunar month needs to be added every 2 to 3 years. Since the early Han Dynasty, a lunar
month without major solar term has been adopted as a leap month. Such a practice remains generally valid
today in most situations.

Related Applications and Customselated Applications and Customs
R
While calendar systems of other places only consist of winter solstice (longest nighttime), summer solstice
(longest daytime[2]), vernal equinox and autumnal equinox (equal day and night), the Chinese calendar
featuring “24 solar terms” provide detailed guidelines and timetable for agricultural activities, e.g. cultivating
rice on “corn on ear”, barley on “cold dew” and bean on “frost”. The themes of “24 solar terms” are also
popularly quoted in Chinese poetry, such as “Bright and Clear (Ching Ming)” by Du Mu, “Around Winter
Solstice” by Du Fu, and “Severe Cold” by Lu You.

Nowadays, urban dwellers still retain some customs linked to the “24 solar terms”, such as family gathering on
“winter solstice is more important than the New Year”, and the culinary practices of having dumpling on
“winter solstice” and spring roll on “spring commences”. With more extensive cultural exchanges, the “24 solar
terms” have been made known to people in other parts of the world and deservedly added to the “UNESCO
World Intangible Cultural Heritage” list in 2016.

N
Noteote
[1]: Along the elliptical Earth’s orbit, di erent segments with the same angular distance correspond to
different time spans.
[2]: In the northern hemisphere, daytime is longest at summer solstice and shortest at winter solstice.

Longitude on ecliptic Major solar Minor solar Corresponding Corresponding dates on Category
coordinate terms terms lunar month Gregorian calendar

0 vernal 2nd month 20-22 Mar Astronomy or
equinox season