What Are the 24 Solar Terms? Origin and Meaning Explained

Last updated: 2026-06-25

Definition of the 24 Solar Terms

The 24 solar terms (二十四節氣, jieqi) are a way of dividing the year into 24 segments based on the changing position of the Sun. The line that projects Earth's orbital plane onto the sky is called the ecliptic, and the angle along it at which the Sun appears is the ecliptic longitude. Starting from the spring equinox, where the Sun's ecliptic longitude is 0 degrees, a new term begins every 15 degrees, and dividing 360 by 15 gives exactly 24 terms.

The 24 solar terms are often mistaken for being lunar, but they are determined by the position of the Sun rather than the movement of the Moon, so they are essentially closer to the solar calendar. That is why Ipchun falls around February 4 almost every year and the winter solstice around December 22, with consistent solar dates. In the era when the lunar calendar was used, the solar-based terms were employed alongside it to correct the drift between the seasons and lunar dates and to set the timing of farm work — that was the role of the 24 solar terms.

Origin of the 24 Solar Terms

The 24 solar terms were developed in the Yellow River basin of ancient China to meet the needs of an agricultural society. At first there were only four terms — the spring equinox, summer solstice, autumn equinox, and winter solstice (the two equinoxes and two solstices) — and adding the starts of the four seasons (Ipchun, Ipha, Ipchu, Ipdong) made eight. Later the gaps between them were subdivided further, and by the Han dynasty today's system of 24 terms was complete. They were transmitted to Korea before the Three Kingdoms period and became an important benchmark for farming and seasonal customs.

Traditionally a month contains two terms: the first is the sectional term (節氣) and the second is the mid-term (中氣). For example, the first lunar month contains Ipchun (sectional term) and Usu (mid-term). One method aligned the lunar calendar with the seasons by designating a month with no mid-term as a leap month (the rule of no-mid-term leap insertion, 無中置閏法).

The 24 Solar Terms by Season

The 24 solar terms are arranged six per season across spring, summer, autumn, and winter. The table below summarizes each term's ecliptic longitude, approximate solar date, and meaning. For the exact date in any given year, use the 24 solar terms calculator.

The Meaning of Key Solar Terms

Ipchun is the first term announcing the start of spring; traditionally, phrases such as "Ipchun daegil" (great fortune at the start of spring) were posted on gates or pillars to pray for a year of good luck. The spring equinox and autumn equinox are when day and night are equal in length, marking the turning points after which the day grows longer or shorter. The summer solstice is the longest day in the Northern Hemisphere, and the winter solstice is the longest night.

The winter solstice in particular was treated as important enough to be called the "little New Year." Because the days begin to lengthen again after the solstice, it was seen as the rebirth of the Sun, and the custom of cooking red bean porridge to ward off bad luck and welcome the new year has been handed down. At Gyeongchip, frogs awaken from hibernation, and Cheongmyeong and Gogu mark the start of the farming season in earnest. After Cheoseo, the heat eases — as the saying goes, "after Cheoseo, even the mosquitoes' mouths go crooked."

The 24 Solar Terms Today

In modern life people rarely track the terms directly, but they are still widely used as a gauge of weather and seasons. Sayings such as "the cold of Ipchun" and "Daehan froze to death visiting Sohan's house" are based on the terms. In farming, fishing, traditional medicine, and cooking, the terms serve as practical benchmarks, and seasonal customs such as winter-solstice red bean porridge and Ipchun couplets continue.

Because the 24 solar terms are based on the Sun, they reflect seasonal change more accurately than the lunar calendar. Since the term dates are set by astronomical calculation, the exact times follow the almanac of the Korea Astronomy and Space Science Institute (KASI). The 24 solar terms calculator on this site is a reference tool that shows each year's term dates using an astronomical approximation.

Summary

• The 24 solar terms divide the ecliptic into 24 equal 15-degree segments based on the Sun, making them essentially close to the solar calendar.
• They consist of six terms each for spring, summer, autumn, and winter, with Ipchun, the summer solstice, the autumn equinox, and the winter solstice being the most notable.
• The spring and autumn equinoxes have equal day and night; the summer solstice has the longest day and the winter solstice the longest night.
• You can check the exact term dates for any year with the 24 solar terms calculator.

Last updated: 2026-06-25