The 24 Solar Terms


The 24 Solar Terms

        The 24 solar terms is a gross name of the system that comprises of 12 major solar terms and 12 minor solar terms interlaced with each other.  Starting from "vernal equinox", the 12 major solar terms are "vernal equinox", "corn rain", "corn forms", "summer solstice", "great heat", "end of heat", "autumnal equinox", "frost", "light snow", "winter solstice", "severe cold" and "spring showers".  Each major solar term falls on one of the 12 lunar months designated by the 12 earthly branches (Figure 1).  The minor solar term after "vernal equinox" is "bright and clear", and then in turn "summer commences", "corn on ear", "moderate heat", "autumn commences", "white dew", "cold dew", "winter commences", "heavy snow", "moderate cold", "spring commences" and "insects waken".

        From the Earth's perspective, the Sun moves through a year across the stars or celestial sphere along a path known as the ecliptic, which is measured in 360 degrees longitude.  The 24 solar terms divide the ecliptic into 24 equal segments, with 15 degrees of the Sun's longitude between the terms.  At "vernal equinox", the Sun's longitude is  0 degree; at "bright and clear", the Sun's longitude is 15 degrees; and so forth (Table 1).

         Table 1             The 24 solar terms and the Sun's longitudes

Major solar term

Vernal Equinox


Corn Rain


Corn Forms


Summer Solstice


Minor solar term


Bright and Clear


Summer Commences


Corn on Ear


Moderate Heat

Sun's longitude

0 deg.

15 deg.

30 deg.

45 deg.

60 deg.

75 deg.

90 deg.

105 deg.

Major solar term

Great Heat


End of Heat


Autumnal Equinox




Minor solar term


Autumn Commences


White Dew


Cold Dew


Winter Commences

Sun's longitude

120 deg.

135 deg.

150 deg.

165 deg.

180 deg.

195 deg.

210 deg.

225 deg.

Major solar term

Light Snow


Winter Solstice


Severe Cold


Spring Showers


Minor solar term


Heavy Snow


Moderate Cold


Spring Commences


Insects Waken

Sun's longitude

240 deg.

255 deg.

270 deg.

285 deg.

300 deg.

315 deg.

330 deg.

345 deg.

        At "vernal equinox" and "autumnal equinox", the periods of daylight and the night are equal in length.  The period of daylight is the longest at "summer solstice" and the shortest at "winter solstice" (northern hemisphere).  These were the earliest solar terms determined in ancient time.  Then it came the four solar terms "spring commences", "summer commences", "autumn commences" and "winter commences".  Other solar terms were named later according to the weather and agricultural activities prevalent at the respective times of the seasons.  The "24 solar terms" reflects to some extent the climate over central China in ancient time.

        Each lunar month in the Agricultural Calendar contains a major solar term.  A lunar month that does not include a major solar term is taken as the leap month of the preceding month.  In 19 tropical years there will be 228 major solar terms and 235 synodic months.  So 7 lunar months will not contain major solar terms and they are classified as leap months.

The 24 Solar Terms and the 12 Zodiac Constellations

        Similar to the 24 solar terms, the 12 zodiac constellations were determined in the ancient time by dividing the zodiac (a band around the ecliptic) into 12 equal sectors measuring from the "vernal equinox" (Figure 2).  Hence the start or end date of each zodiac sign in astrology always falls within about one day on a major solar term.

Remarks:        The determination of the 12 zodiac constellations according to the Sun's longitude was made more than 2000 years ago.  Due to precession of the Earth's rotation axis, the positions of the constellations as observed nowadays have already shifted to other longitudes.


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