of thumb about the Gregorian dates of jieqi, namely: Two jieqi per month; Gregorian dates are off by one or two days at most; In the first half of the year, jieqi happens around the 6th and 21st day of each (Gregorian) month; In the second half of the year, jieqi happens around the 8th and 23rd day of each (Gregorian) month. Determination The modern definition using ecliptic longitudes, introduced by the Shixian calendar, is known as . Under this method, the determination of solar terms is similar to the astronomical determination of the special cases of equinox and solstice dates, with different ecliptic longitudes to solve for. One can start with an approximation and then perform a correction using the anomalies and mean motion of the sun. The JPL Horizons On-Line Ephemeris System may be used to query for exact times of solar terms. The older method is known as and simply divides the tropical year into 24 equal parts. Regional note In Japan, the term () originally referred to the eves of (, 315°, the beginning of Spring), (, 45°, the beginning of Summer), (, 135°, the beginning of Autumn), and (, 225°, the beginning of Winter), but currently mostly refers to the day before . The name of each solar term also refers to the period of time between that day and the next solar term, or 1/24th of a year. See also Chinese calendar Korean calendar Japanese calendar Vietnamese calendar References External links 24 Solar Terms calculator 24 Solar Terms – Hong Kong Observatory Twenty Four Solar Terms and Their Customs in China Chinese calendar with upcoming solar terms in current year 24 Sekki – NAOJ > ECO > Glossary > Twenty-four Solar Terms and meaning Date and time of Solar Terms The 24 Solar Terms Intangible Cultural Heritage of Humanity