24 Solar TermsThe seasonal architecture of the Chinese calendar
The 24 Solar Terms divide the Sun’s annual path into 15-degree intervals. Together they describe a precise seasonal cycle used in agriculture, traditional culture, BaZi month and year boundaries, and timing systems.
The astronomical framework
24 × 15°A complete 360° cycle.
Each term begins when the Sun reaches its defined ecliptic longitude.
What are the 24 Solar Terms?
A seasonal clock built from the Sun.
The terms divide the apparent annual solar path into twenty-four equal angular segments. Each boundary has an exact astronomical moment, though the local civil date and time can vary by year and timezone.
They originated as a detailed seasonal language for agriculture and remain central to Chinese calendrical work, traditional observance, and BaZi calculation.
Lunar months begin with the new moon. BaZi solar months begin at the twelve sectional terms. These are related calendar layers—not the same boundary.
The operating pattern
Two terms share each Earthly Branch month.
Sectional terms · 節
The first term in each pair begins a new BaZi solar month and Earthly Branch assignment.
Major terms · 中氣
The second term develops the seasonal condition within that same branch month.
Angular interval
Every transition advances the defined solar longitude by fifteen degrees.
Time interval
Terms occur roughly fifteen days apart, with exact timing set astronomically.
315° → 30°
Spring · emergence and expansion
立春 · Beginning of Spring
The solar year and Yin month begin; spring movement first emerges.
雨水 · Rain Water
Moisture increases and the seasonal thaw becomes more visible.
驚蟄 · Awakening of Insects
The Mao month begins; dormant life responds to warming conditions.
春分 · Spring Equinox
Day and night approach balance as spring reaches its midpoint.
清明 · Pure Brightness
The Chen month begins; clarity, growth, and Qingming observance converge.
穀雨 · Grain Rain
Rain supports crops as spring moves toward summer.
45° → 120°
Summer · growth and culmination
立夏 · Beginning of Summer
The Si month begins and summer Qi becomes established.
小滿 · Grain Full
Crops begin filling, though full maturity has not arrived.
芒種 · Grain in Ear
The Wu month begins; sowing and grain work intensify.
夏至 · Summer Solstice
Daylight reaches its annual maximum before gradually declining.
小暑 · Minor Heat
The Wei month begins as heat becomes pronounced.
大暑 · Major Heat
The seasonal heat reaches its strongest phase.
135° → 210°
Autumn · harvest and contraction
立秋 · Beginning of Autumn
The Shen month begins; autumn emerges within lingering heat.
處暑 · End of Heat
Intense summer heat begins to withdraw.
白露 · White Dew
The You month begins; cooler nights make dew more visible.
秋分 · Autumn Equinox
Day and night approach balance at autumn’s midpoint.
寒露 · Cold Dew
The Xu month begins and coolness becomes more penetrating.
霜降 · Frost Descent
Frost signals the deepening transition toward winter.
225° → 300°
Winter · storage and renewal
立冬 · Beginning of Winter
The Hai month begins; winter storage and contraction take hold.
小雪 · Minor Snow
Colder conditions arrive, with early snow in relevant climates.
大雪 · Major Snow
The Zi month begins as winter intensifies.
冬至 · Winter Solstice
Night reaches its annual maximum and returning Yang is symbolically marked.
小寒 · Minor Cold
The Chou month begins amid deep winter cold.
大寒 · Major Cold
The coldest phase closes the cycle before Li Chun.
Why the terms matter in BaZi
They keep the pillars in season.
BaZi year and month boundaries follow the solar-term system, preventing the chart from drifting with variable lunar-month dates.
Why solar terms matter
One system, several uses.
Year and month boundaries
Solar terms anchor the seasonal pillars and protect charts near transition dates from calendar drift.
Seasonal observation
The names preserve practical attention to temperature, rainfall, dew, frost, growth, harvest, and storage.
Seasonal Qi context
Timing and compass practices may relate directional work to the changing seasonal field.
Ritual and observance
Terms such as Qingming and the solstices carry cultural meanings beyond technical calculation.
Exact-term workflow
Check the moment, not only the date.
- Identify the term and target year.
- Use a reliable astronomical term listing.
- Convert the transition into the local timezone.
- Compare the event or birth time to the exact boundary.
- Record the source, timezone, and assigned branch month.
Common mistakes
Keep the calendar layers distinct.
- Assuming lunar months begin at solar terms.
- Treating approximate dates as exact transition times.
- Ignoring timezone for a boundary birth.
- Using all 24 terms as separate BaZi months.
- Applying historic climate names literally in every region.
Explore further
Connect season, calendar, and chart.
Seasonal precision
Twenty-four terms. Twelve BaZi months. One continuous solar year.
Use the full sequence to understand seasonal change—and the twelve sectional boundaries to calculate the solar months correctly.