Sources & credits

The data and methods behind the charts and the sky. Updated July 2026.

The tradition

The four pillars, the ten heavenly stems and twelve earthly branches, the sexagenary cycle, the ten gods, the twelve stages and the solar terms are ancient, unowned knowledge, far older than any copyright term. Gilsung computes them from first principles with its own tables. Every line of interpretive writing in the app is original and was written for it; none is taken from a modern author.

Calendar and solar terms

Solar terms are computed from the Sun's apparent longitude, with the year beginning at lichun (Sun at 315 degrees) and months at the sectional terms. The solar-longitude quantity comes from the VSOP87 planetary theory (Bretagnon and Francou, Bureau des Longitudes) with standard algorithms from Jean Meeus, Astronomical Algorithms. These are published scientific methods; the implementation is entirely Gilsung's own.

The twenty-eight mansions

The 二十八宿 and their determinative stars are facts of an ancient system. Star coordinates and magnitudes come from the Hipparcos catalogue, the Yale Bright Star Catalogue and the HYG compilation. Factual astronomical measurements are not subject to copyright.

Constellation figures

Where the sky view draws Western constellation figures alongside the mansions, those stick figures are derived from the official IAU constellation figures by Sky & Telescope (Alan MacRobert, Roger Sinnott, Rick Fienberg), used under the Creative Commons Attribution (CC BY) licence.

The name and the marks

Gilsung is 吉星, the auspicious star: a real term in 命理 for the favourable stars in a chart, and the idiom 吉星高照. The wordmark is set in Didot with a gold-leaf texture. The seal is a cinnabar name-chop carrying 四柱, the four pillars, in traditional characters, native-confirmed and never simplified.

Typefaces

This site is set in Fraunces and Mulish, both offered under the SIL Open Font License and bundled here so your visit is never tracked by a font host. CJK and Thai text is rendered in your own device's system fonts.

Contact

Questions: hello@gilsung.app