# 24 Solar Terms Calculator (二十四节气)

> Lists the 24 solar terms (节气 jieqi) of a Gregorian year with their exact instants: the moments the Sun's apparent longitude reaches multiples of 15°, computed astronomically and shown in a chosen UTC offset (China Standard Time by default).

- Calculator id: `solar-terms` · Category: Chinese Calendar (`lunar`) · Tool name: `list_solar_terms`
- Canonical page: https://tttkmbb.com/lunar/solar-terms · This document: https://tttkmbb.com/lunar/solar-terms.md · JSON definition: https://tttkmbb.com/lunar/solar-terms.json

## Purpose

Lists the 24 solar terms (节气 jieqi) of a Gregorian year with their exact instants: the moments the Sun's apparent longitude reaches multiples of 15°, computed astronomically and shown in a chosen UTC offset (China Standard Time by default).

**Use when:** You need the date or time of 立春, 清明, 夏至, 冬至 or any other solar term in a given year, or the full 24-term table.

**Do not use when:** You only need the term that a specific date falls in (use lunar-calendar-converter), or you need sunrise/sunset times (use sunrise-sunset).

## Input

| Parameter | Type | Unit | Required | Description |
| --- | --- | --- | --- | --- |
| `year` | integer |  | required | Gregorian calendar year (1900–2100). (min 1900, max 2100) |
| `utc_offset_hours` | number | h | optional, default 8 | Fixed UTC offset in hours for the local date-times (8 = China Standard Time; 9 = Japan/Korea; 5.5 = India). (min -12, max 14) |

## Output

| Field | Type | Unit | Description |
| --- | --- | --- | --- |
| `terms` | list |  | 24 rows in calendar order (小寒 first): name_cn, pinyin, english, solar_longitude (°), datetime_local, datetime_utc, date, type (major 中气 / minor 节). |
| `lichun_date` | string |  | Local date and time (HH:MM) of 立春, the start of the solar-term year. |
| `spring_equinox` | string |  | Local date and time of 春分 (Sun at 0°). |
| `summer_solstice` | string |  | Local date and time of 夏至 (90°). |
| `autumn_equinox` | string |  | Local date and time of 秋分 (180°). |
| `winter_solstice` | string |  | Local date and time of 冬至 (270°). |
| `year_ganzhi` | string |  | Sexagenary name of the year with pinyin and element/animal. |
| `suishou_note` | string |  | When the sexagenary year begins under solar-term reckoning (立春) versus the lunar calendar (Chinese New Year). |
| `utc_offset` | string |  | Offset applied to datetime_local and date. |

## Formula

`term instant: apparent geocentric solar longitude λ(JDE) = k·15° for k = 0 (春分) … 23 (惊蛰), solved by Newton iteration; UT = TT − ΔT; local time = UT + utc_offset_hours`

Solar longitude from the VSOP87 series subset in Meeus (the series also used by the NREL SPA) with nutation and aberration, ΔT from the Espenak–Meeus polynomials; accuracy about ±1 minute (larger far from the present because ΔT is extrapolated), matching the Hong Kong Observatory times to the minute for the checked years. Times are rounded to the minute. Traditional calendar/cultural reference calculation; not a prediction, medical, legal or financial advice.

## Data Sources

- Solar term (Wikipedia) — https://en.wikipedia.org/wiki/Solar_term (reference, retrieved 2026-09-24)
- Hong Kong Observatory – Gregorian-Lunar Calendar Conversion Table — https://www.hko.gov.hk/en/gts/time/conversion.htm (government, retrieved 2026-09-24)
- Meeus J. (1998) Astronomical Algorithms, 2nd ed., Willmann-Bell (solar longitude, nutation, ΔT, new moons) — https://en.wikipedia.org/wiki/Jean_Meeus (textbook, retrieved 2026-09-24)

Data freshness: `static`. Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output.

## API

- `GET https://tttkmbb.com/api/v1/calculate/solar-terms?year=…`
- `POST https://tttkmbb.com/api/v1/calculate/solar-terms` with JSON body `{"inputs": {…}}`
- Response: unified envelope (`success`, `request`, `result.values`, `result.units`, `sources`, `freshness`, `timestamp`, `next_actions`, `links`); see https://tttkmbb.com/docs/response-format.md
- Schema: https://tttkmbb.com/api/v1/calculators/solar-terms · OpenAPI operationId `list_solar_terms` in https://tttkmbb.com/openapi.json
- Authentication: none. Rate limit: fair use, see https://tttkmbb.com/docs/rate-limits.md.

## MCP

- Server: `https://tttkmbb.com/mcp` (Streamable HTTP, JSON-RPC 2.0, no auth)
- Tool:  `run_calculator` with `{"calculator_id": "solar-terms", "inputs": {…}}`

## Example

- 2024 (China Standard Time): inputs `{"year":2024,"utc_offset_hours":8}` → `{"lichun_date":"2024-02-04 16:27","winter_solstice":"2024-12-21 17:20","summer_solstice":"2024-06-21 04:51","spring_equinox":"2024-03-20 11:06"}`
- 2026 立春: inputs `{"year":2026,"utc_offset_hours":8}` → `{"lichun_date":"2026-02-04 04:02"}`

```
GET https://tttkmbb.com/api/v1/calculate/solar-terms?year=2024&utc_offset_hours=8
```

## Limitations

You only need the term that a specific date falls in (use lunar-calendar-converter), or you need sunrise/sunset times (use sunrise-sunset). Solar longitude from the VSOP87 series subset in Meeus (the series also used by the NREL SPA) with nutation and aberration, ΔT from the Espenak–Meeus polynomials; accuracy about ±1 minute (larger far from the present because ΔT is extrapolated), matching the Hong Kong Observatory times to the minute for the checked years. Times are rounded to the minute. Traditional calendar/cultural reference calculation; not a prediction, medical, legal or financial advice. All values are computed from the formula above; no measurement or live data is involved.

## FAQ

**Why do some sources give a different date for a term?**

The date depends on the time zone: a term at 00:30 Beijing time falls on the previous day in UTC. Published Chinese almanacs use UTC+8, which is the default here.

**What is the difference between 节 and 中气?**

The 24 terms alternate: the 12 minor terms (节, odd multiples of 15°: 立春, 惊蛰 …) start the sexagenary months; the 12 major terms (中气, even multiples: 雨水, 春分 …) fix the lunar month numbers and decide which month becomes a leap month.

## Related

- [Lunar Calendar Converter (农历)](https://tttkmbb.com/lunar/lunar-calendar-converter.md) — Which solar-term period a date falls in.
- [Chinese Festival Dates Calculator](https://tttkmbb.com/lunar/chinese-festivals.md) — Festival dates, 三伏 and 数九 periods derived from the solstices.
- [Sunrise and Sunset Calculator](https://tttkmbb.com/time/sunrise-sunset.md) — Sunrise and sunset for the same date and a location.