24 Solar Terms Date Lookup Calculator

What Is a Solar Term?

A solar term is an astronomical point in the Sun's annual apparent motion. The traditional Chinese calendar divides the Sun's path along the ecliptic into 24 successive positions, separated by 15° of solar longitude.

The terms therefore correspond to astronomical positions rather than fixed Gregorian calendar dates. The calendar date and clock time at which a solar term begins can vary slightly from year to year.

The Twenty-Four Solar Terms developed from observations of seasonal and astronomical changes in China and remain part of a traditional system of timekeeping and seasonal knowledge. UNESCO inscribed the Twenty-Four Solar Terms on the Representative List of the Intangible Cultural Heritage of Humanity in 2016. UNESCO — The Twenty-Four Solar Terms.

How the Solar Terms Are Calculated

The calculator treats each solar term as an astronomical event, rather than as a fixed calendar date.

1. Solar longitude. The position of the Sun is expressed as its apparent longitude along the ecliptic. Solar longitude provides a continuous astronomical measure of the Earth's position in its seasonal orbit.
2. The 24 solar-term boundaries. The Twenty-Four Solar Terms divide the annual solar cycle into 24 successive boundaries, separated by 15° of solar longitude. For example, Spring Equinox is 0°, Grain Rain 30°, Summer Solstice 90°, Autumn Equinox 180°, and Winter Solstice 270°.
3. Finding the exact moment. For each term, the calculation determines the moment when the Sun reaches its designated solar longitude, producing an astronomical instant rather than simply assigning the term to a conventional calendar day.
4. Converting the result to calendar time. The astronomical instant is expressed as a date and time using Beijing Time (UTC+8), the reference convention used by this calculator.
5. Verification. The 1950–2100 solar-term table is calculated from a VSOP87-derived solar-position model and checked against published astronomical reference times, including equinox and solstice instants.

Why Do Solar Term Dates Change Every Year?

The 24 Solar Terms do not fall on exactly the same Gregorian date every year. This is because each term is defined by the astronomical position of the Sun, not by a fixed number on the Gregorian calendar.

The Earth's orbital motion is not perfectly uniform, so the relationship between an astronomical event and a calendar date changes slightly from year to year. A solar term may therefore begin on different calendar dates or at different times in different years. For this reason, a solar-term calculator is more precise than using a fixed annual date such as “February 4” for Start of Spring or “March 21” for the Spring Equinox.

For a deeper explanation of how the 15-degree divisions determine the timing of the solar terms, see how solar terms work.

Why Time Zones Matter

A solar term begins at one astronomical instant, but that instant can correspond to different local calendar dates. If a solar term begins late at night in Beijing, it may still be the previous calendar date in London or North America. This is why two calendars can show different dates for the same solar term without either calculation being incorrect.

This calculator expresses solar-term times using Beijing Time (UTC+8). The astronomical event itself does not change; only its local calendar representation changes with the time zone.

The 24 Solar Terms at a Glance

Solar longitude uses the astronomical convention of 0° at the Spring Equinox. Each term links to its full page. Dates are intentionally omitted: a term's date is the result of a calculation, not a fixed value.

Solar Terms and the Zodiac

Solar terms and Western zodiac signs are different systems. Both can be described using positions along the ecliptic, but the Twenty-Four Solar Terms are part of a traditional calendrical system, while Western zodiac signs belong to a different astronomical and astrological framework. Solar terms are astronomical calendar markers, not astrological signs.

Sources & Methodology

UNESCO

The Twenty-Four Solar Terms — inscribed on the Representative List of the Intangible Cultural Heritage of Humanity (2016).

Computational model

VSOP87-derived solar longitude (Shou Xing celestial algorithm).

Astronomical references

Published equinox and solstice instants used for verification.

Calendar convention

Beijing Time (UTC+8).

Frequently Asked Questions

What are the 24 Solar Terms?

They are 24 astronomical markers that divide the Sun's apparent path along the ecliptic into successive 15° segments. Each marks the moment the Sun reaches a given solar longitude, tracking the seasonal cycle of the traditional Chinese calendar.

Are the Solar Terms fixed dates?

No. Each term is defined by the Sun's astronomical position, not by a fixed number on the Gregorian calendar, so its date and clock time shift slightly from year to year. A calculator is more precise than assuming a fixed date such as "February 4" for Start of Spring.

What time zone does this calculator use?

Results are expressed in Beijing Time (UTC+8), the reference convention of the traditional calendar. The stored astronomical instants are UTC; eight hours are added to give the Beijing calendar date.

Why can two websites show different Solar Term dates?

A solar term begins at a single astronomical instant, but that instant can fall on different local calendar dates depending on the time zone. Both results can be correct — only the local representation differs.

How accurate is the calculator?

Solar-term instants are computed from a VSOP87-derived solar-position model and checked against published equinox and solstice reference times to within one minute.

What years does the calculator cover?

Every solar term from 1950 through 2100, at minute-level precision.

Are Solar Terms the same as zodiac signs?

No. Solar terms are astronomical calendar markers, not astrological signs. The zodiac cross-reference reflects the shared ecliptic coordinate system only; the two belong to different frameworks.