A sequence of solar longitudes
The 24 solar terms mark successive 15° intervals of the Sun’s ecliptic longitude. HKO’s table places the vernal equinox at 0° and Spring Commences, Li Chun, at 315°. A term is an astronomical boundary, not a fixed annual civil date.
When comparing timestamps, distinguish the instant of the boundary from the local date printed on a calendar. Timezone conversion can place that same instant on different dates.
Hong Kong Observatory · Solar terms and their solar longitudes ↗
How the BaZi explorer uses the terms
Atlas’s declared BaZi method takes alternating solar terms as month boundaries. The seasonal receipt shows the current longitude and the start and end longitudes for the selected solar month. These are the inputs to this method’s month classification, not a direct reading of a Chinese lunar month.
Keep the current longitude, year boundary and month boundary together when checking a result. Near a boundary, first compare time conventions and ephemeris settings. A different chart label alone does not identify which calculation is wrong.
Seasonal names need geographic context
HKO relates the names to seasonal and agricultural conditions in historical central China. The labels therefore do not describe the weather everywhere on Earth. Their use in a chart is a calendar convention; an interpretive claim requires its own attributed teaching.
HKO also distinguishes the solar terms’ role in the traditional lunisolar calendar from the sequence of lunar months. The Atlas solar-month receipt should be read as its named BaZi convention rather than a replacement for that calendar.
Hong Kong Observatory · Solar terms and their solar longitudes ↗
Word origin · etymology
English calendrical translation.
Solar identifies the Sun-based divisions called jiéqì, 節氣. Term carries the sense of a marked division or period in the seasonal year.
How we know · epistemology
Astronomical seasonal marker
Each term is fixed by a tropical solar longitude, making its instant calculable. Its local calendar date depends on time conversion, while associated seasonal descriptions reflect the cultural and geographic setting of the calendar.
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These links connect subjects and terminology. They do not establish a shared historical origin.
Sources & provenance
Use the citations beside each section to distinguish a calculation convention, a historical teaching and an editorial example.