二十四节气交节时刻

Subscribe: add the twenty-four solar terms (2027–2036) to your calendar (.ics, 60 KB)

Solar terms: the twenty-four instants, to the second (China Standard Time)

A solar term (节气) begins at the instant the Sun’s apparent geocentric ecliptic longitude reaches
a multiple of 15°. The convention follows GB/T 33661-2017, Calculation and promulgation of the
Chinese calendar. All instants below are China Standard Time (UTC+8).

2026

Method and cross-check

Each instant is solved for the moment the Sun’s apparent geocentric ecliptic longitude reaches that
term’s longitude, using the NASA JPL DE421 ephemeris, whose coverage runs from 1899-07-28 to
2053-10-08. Precession and nutation are applied, light-time is accounted for, and the result is
converted from TT to UTC with a ΔT model before being expressed in China Standard Time. The defining
convention — the Sun’s apparent geocentric longitude reaching an exact multiple of 15° — is the one
set out in GB/T 33661-2017, Calculation and promulgation of the Chinese calendar.

The numbers were then compared term by term against the 24 official values in the Purple Mountain
Observatory’s Calendar data for 2026. The largest disagreement is 30 seconds and the mean is 11.4
seconds. Because the official values are published only to the minute, all 24 agree to the published
precision.

Two points are worth stating plainly, because they are the ones people ask about. First, these are
instants of the Sun’s apparent geocentric longitude, so they carry no dependence on any observing
site: the same table is valid for every place on Earth, and only the local clock reading differs.
Second, a term’s longitude value is fixed by definition, so any disagreement between two
implementations comes from the ephemeris, the time-scale handling or the ΔT model, not from the
definition itself — which is exactly what makes a term-by-term comparison useful.

Coverage, and how to get the data

The full 1900–2052 set, year by year and term by term, to the second, is published here:
Chinese Calendar Public Dataset (CC BY 4.0, DOI
10.5281/zenodo.22788686, source on GitHub). The computation engine, time scales and cross-check
conventions are described under Data and Methods.

Term names are given in Chinese with pinyin and an English gloss, the convention used throughout
this site’s English pages.

Scope

Modern back-calculation, not prediction. Astronomical reference only — no astrology,
prognostication or fortune-telling.