The 24 Solar Terms 用英语讲中国16|二十四节气

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. 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.

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.

24节气

二十四节气是一个统称，其中包括十二个中气和十二个节气，中气和节气相间地排列。

从春分起十二个中气分别是春分、谷雨、小满、夏至、大暑、处暑、秋分、霜降、小雪、冬至、大寒和雨水，分属于12个以地支排列的月份。春分后的节气是清明，其后的节气依次是立夏、芒种、小暑、立秋、白露、寒露、立冬、大雪、小寒、立春和惊蛰。

从地球上观测，太阳一年里在恒星间或天球划过的轨道称为黄道，以360度黄经来量度。二十四节气正好把黄道分成24等份，即每个节气相差黄经15度。春分时黄经为0度，清明时黄经为15度，依此类推。

春分和秋分昼夜平分，夏至昼最长（北半球，下同），冬至昼最短，春分、秋分、夏至和冬至是古人最初确立的节气。其后加入的是立春、立夏、立秋和立冬。至于其他的节气，便以该段季节常见的天气现象或农业活动而命名，这些节气从某种程度上反映了古代中原地区的气候。

农历规定每一个月必定要有一个中气，没有中气的月份，便成为前一个月的闰月。原来19个“回归年”共有228个中气和235个“朔望月”，即有7个月没有中气，这些没有中气的月便正好成为闰月。