Formula · Astronomy and calendar
Solar terms mark the sun every 15 degrees of ecliptic longitude. The start of spring sits at 315 degrees and can be computed from an ephemeris rather than estimated. We use it only to fix where the year pillar changes.
Ephemeris-grade astronomy, independently verifiable
Astronomy and calendar
This one is astronomy and calendar: verifiable against civil dates and solar-term tables.
Related: calendar and the day boundary · all formulas · tools
Where is this formula used?
It is the same entry listed on the method page, used in pages such as calendar and the day boundary; the link above shows it in context.
Did you invent this formula?
This one is astronomy and calendar: verifiable against civil dates and solar-term tables.