The traditional Chinese calendar is lunisolar in nature. Each month starts on a new moon while the middle of the month is always the full moon. The months alternate between 29 and 30 days to account for the fact that the moon takes 29.5 days to rotate around the earth. While this systems makes it very easy to count months, it would not have been useful for agricultural purposes since the lunar year of 354 days would constantly be out of synchronization with the actual position of the earth relative to the sun and therefore would have been a poor predictor of weather conditions.
A parallel system was therefore overlayed on top of the lunar system. This parallel system, called a 節氣/节气 jiéqi or solar term, divides each year into 24 positions of the sun along the ecliptic, i.e. the apparent path path of the sun among the constellations in the course of a year. The solar terms are spaced 15° degrees apart. The even-numbered terms are considered major solar terms while the odd-numbered ones are considered minor. The summer and winter solstice and the spring and autumnal equinox are four of these major solar terms. The other solar terms are evenly spaced between these points and have names that readily indicate the expected weather conditions. For example, solar term #10 (Summer Solstice, around Jun 21) is followed by #11 (Slight Heat, around July 6), #12 (Great Heat, around July 22), etc. Although the descriptive names were designed for central China, anyone living in the northern hemisphere today can still already relate to significance of the solar terms and their names. Apart from the solar terms that mark solstices and equinoxes, most of the remaining solar terms describe weather conditions (e.g. Rain Water, Cold Dew) and prevalent natural phenomena for that time of the year (e.g. Insects Waken, Grain in Ear). The overall effect is that the year is clearly divided into 24 mini-seasons which would serve as a useful farmers' almanac. In fact, the traditional Chinese calendar is called 農曆/农历 or the Agricultural Calendar.
The first solar term is 立春 or Spring Begins, which begins around February 4. Interestingly, the first solar term can start even before the start of the lunar year. Two of the solar terms dictate some very important holidays. The Qingming holiday (Tomb Sweeping Day) happens at the beginning of the fifth solar term (also called 清明 or Pure Brightness). The Dongzhi Festival, on the other hand is always at the beginning of the twenty second solar term (冬至 or Winter Solstice).
One additional very important function of the solar terms is that it governs the timing for adding leap months that need to be added about every three years in order to get the calendar back in sync with the position of the sun.
| # | Name | Sun Angle | Gregorian Date | Lunar Date | ||
|---|---|---|---|---|---|---|
| 23 | 小寒 | Slight Cold | 285° | Jan 5, 2026 | 2025年 冬月 十七 | |
| 24 | 大寒 | Great Cold | 300° | Jan 20, 2026 | 2025年 腊月 初二 | |
| 1 | 立春 | Spring Begins | 315° | Feb 4, 2026 | 2025年 腊月 十七 | |
| 2 | 雨水 | Rain Water | 330° | Feb 18, 2026 | 2026年 正月 初二 | |
| 3 | 驚蟄 | Insects Waken | 345° | Mar 5, 2026 | 2026年 正月 十七 | |
| 4 | 春分 | Spring Equinox | 0° | Mar 20, 2026 | 2026年 二月 初二 | |
| 5 | 清明 | Pure Brightness | 15° | Apr 5, 2026 | 2026年 二月 十八 | |
| 6 | 穀雨 | Grain Rain | 30° | Apr 20, 2026 | 2026年 三月 初四 | |
| 7 | 立夏 | Summer Begins | 45° | May 5, 2026 | 2026年 三月 十九 | |
| 8 | 小滿 | Grain Full | 60° | May 21, 2026 | 2026年 四月 初五 | |
| 9 | 芒種 | Grain in Ear | 75° | Jun 5, 2026 | 2026年 四月 二十 | |
| 10 | 夏至 | Summer Solstice | 90° | Jun 21, 2026 | 2026年 五月 初七 | |
| 11 | 小暑 | Slight Heat | 105° | Jul 7, 2026 | 2026年 五月 廿三 | |
| 12 | 大暑 | Great Heat | 120° | Jul 23, 2026 | 2026年 六月 初十 | |
| 13 | 立秋 | Autumn Begins | 135° | Aug 7, 2026 | 2026年 六月 廿五 | |
| 14 | 處暑 | Heat Ends | 150° | Aug 23, 2026 | 2026年 七月 十一 | |
| 15 | 白露 | White Dew | 165° | Sep 7, 2026 | 2026年 七月 廿六 | |
| 16 | 秋分 | Autumnal Equinox | 180° | Sep 23, 2026 | 2026年 八月 十三 | |
| 17 | 寒露 | Cold Dew | 195° | Oct 8, 2026 | 2026年 八月 廿八 | |
| 18 | 霜降 | Frost Descends | 210° | Oct 23, 2026 | 2026年 九月 十四 | |
| 19 | 立冬 | Winter Begins | 225° | Nov 7, 2026 | 2026年 九月 廿九 | |
| 20 | 小雪 | Slight Snow | 240° | Nov 22, 2026 | 2026年 十月 十四 | |
| 21 | 大雪 | Great Snow | 255° | Dec 7, 2026 | 2026年 十月 廿九 | |
| 22 | 冬至 | Winter Solstice | 270° | Dec 22, 2026 | 2026年 冬月 十四 | |
| 23 | 小寒 | Slight Cold | 285° | Jan 5, 2027 | 2026年 冬月 廿八 | |
| 24 | 大寒 | Great Cold | 300° | Jan 20, 2027 | 2026年 腊月 十三 | |