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The 24 Solar Terms

The 24 solar terms are a farming calendar made in ancient China. Farmers watched the sun and the noon shadow of a stick. They cut the year into 24 parts of about 15 days, each with a name that tells what the weather and the fields are doing. Four of them start the seasons, two are solstices and two are equinoxes. The calendar follows the sun, so the dates stay almost the same every year.

🎬 Step-by-step story

  1. Long ago, farmers did not have clocks or phones. They put a stick in the ground and watched its shadow at noon.
  2. In winter the sun stays low. The shadow is long. This is the winter solstice, the day with the longest night.
  3. In summer the sun climbs high. The shadow is short. This is the summer solstice, the day with the longest daytime.
  4. Twice a year the shadow is in the middle. Day and night are equal. These are the spring and autumn equinoxes.
  5. The sun moves a little every day. Farmers cut one year into 24 steps of about 15 days. Each step has a name, like Rain Water or Frost Falls.
  6. Your turn. Drag the slider through all 24 terms. Watch the shadow, the season colour and the crop.

Tip: drag the 3D scene to turn it. Use two fingers to zoom.

🤔 Common doubts, cleared

Why is the shadow long in winter?

The sun is low in the sky in winter, so objects throw long shadows. Step 2 shows it.

Is a solstice a whole season?

No. A solstice is one day, the day of the highest or lowest sun. Step 3 shows summer solstice.

Why 24 and not 12 parts?

Farmers needed finer steps. About 15 days is short enough to say when to sow or harvest. See step 5.

Do the terms match the weather in my town?

Not always. They were made for north China. The sun part (shadow, day length) is true everywhere; the weather part changes by place. Step 6 lets you try.

What is the difference between equinox and solstice?

Equinox: equal day and night, the shadow is middling (step 4). Solstice: longest or shortest day and shadow (steps 2 and 3).

Origin of the 24 solar terms

The 24 solar terms were worked out in the Yellow River valley in ancient China, more than 2,000 years ago. Farmers there had cold winters and hot, rainy summers. They needed to know when to plant and harvest.

How the sun gives the dates

Because the terms follow the sun and not the moon, they fall on nearly the same date every year (for example, the winter solstice is about 21 or 22 December). The old Chinese calendar followed the moon, so it needed the solar terms to keep the seasons right. In 2016 this knowledge was added to the UNESCO list of intangible cultural heritage.

The 8 key terms and the four seasons

Eight terms are the main posts of the year:

Each season holds six terms: two for the start and middle, and others for changes such as rain, heat or frost.

Links to farming and climate

The names are like short weather notes for the farmer.

Names that talk about weather

Names that talk about farm work

The terms were made for north China. In south China or other countries the weather does not match each name exactly, so farmers there add local sayings.

Try it: your own shadow clock

  1. In the 3D, press the dots and see the shadow length change for winter, summer and the equinox.
  2. Predict first: at Minor Heat, will the shadow be longer or shorter than at Lichun? Then drag the slider to check.
  3. At home: stand a stick on flat ground at noon on a sunny day. Mark the shadow tip with a stone. Do it again after two weeks. Is the shadow longer or shorter? (In India, north of the Tropic of Cancer, it grows shorter from winter to summer.)

Key formulas and definitions

Worked examples

1. How many days does one solar term last, roughly?

A year has about 365 days. 365 ÷ 24 is about 15. So each term lasts about 15 days.

2. A stick has a very long noon shadow. Which season is it in north China?

A long shadow means the sun is low. That is winter, and the longest shadow is at the Winter Solstice (about 21 or 22 December).

3. A farmer hears "Grain in Ear". What jobs does he think of?

It is early June. Winter wheat is ripe to harvest, and rice and other summer crops must be planted. It is very busy, so people say the farmers have no free time.

Common mistakes

Practice quiz

1. How many solar terms are in a year?
2. At the winter solstice the noon shadow is:
3. What does each solar term follow?
4. Which term means day and night are equal?
5. Who mainly used the solar terms first?

Practice: answer these yourself

Type or choose your answer, then press Check. Use a hint if you are stuck; the full solution appears after you answer.

Frequently asked questions

What are the 24 solar terms in simple words?

They are 24 named parts of the year, each about 15 days, based on where the sun is. They tell farmers about weather and farm work.

Why are the dates almost the same every year?

Because they follow the sun, and the sun's yearly path repeats. The moon-based calendar moves, but the solar terms stay steady.

Are solar terms still used today?

Yes. Farmers, cooks and families still use them for farming advice, food customs and festivals such as Qingming.

Where this is taught

China八年级（初二）Ch.6 Geographic differences

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