Sources
In short
- The calendar is astronomy and arithmetic, checked against official tables.
- The meanings come from two classical Chinese books, read in the eighteenth-century imperial library edition, and from two classics of Western astrology.
- Every rule in the app names the passage it comes from: the book, the section and the leaf. Every card is written in our own words from those passages.
Two kinds of source
When Sixty Skies says which sky and animal a day carries, it is doing arithmetic: the sixty-day cycle has run without a break for more than two thousand years, and the months follow the sun. That part can be checked, and we check it.
When it says what a day or a chart is like, it is drawing on a symbolic tradition. There is no scientific evidence for these meanings, and we do not claim any. What we can offer is faithfulness: the meanings come from the texts the tradition itself treats as standard, not from invention, and we show where. The app uses them to describe the climate of a day, never to predict events.
The calendar
- The sun’s position decides where the months of the solar year begin. In a birth chart the year turns at the beginning of spring, around 4 February, not at the lunar new year. Positions come from Astronomy Engine, an open-source library that our tests compare with NASA JPL’s Horizons system.
- The day cycle and the months are tested against the Gregorian–Lunar calendar conversion tables of the Hong Kong Observatory, which cover 1901 to 2100.
- The almanac date follows the Chinese national standard for the calendar, GB/T 33661-2017, which counts the day in China Standard Time.
The classical Chinese texts
We read both books in the Siku quanshu, the “Complete Library of the Four Treasuries” that the Qianlong emperor had copied in the 1770s and 1780s, in the Wenyuange copy, through the open transcription of the Kanseki Repository. Both are in the public domain. The translations in the app are our own.
Sanming tonghui
Wan Minying’s Sanming tonghui, roughly “a comprehensive survey of the three fates”, was written in the late sixteenth century, under the Ming dynasty. In twelve books (juan), it gathers what earlier writers had said about reading a birth chart and became one of the standard references of the tradition. A scan of an old printing is open at the Australian National University.
Qinding xieji bianfang shu
The Qinding xieji bianfang shu, “the imperially commissioned book on harmonizing the times and distinguishing the directions”, was compiled by a commission led by Prince Yunlu and completed in 1741. It settled the rules of the official almanac, the book that told each day what it suits: the twelve day qualities, the day spirits, and the lists of what to take up and what to leave.
| In the app | Source | Where |
|---|---|---|
| The five elements, and how they feed and check each other | Sanming tonghui | book 1 |
| How today’s sky meets the element of today’s animal | Sanming tonghui | book 1 |
| Your element, and the ten skies | Sanming tonghui | books 2 and 4 |
| The twelve animals, their seasons and the skies inside them | Sanming tonghui | book 2 |
| The ten roles, and the birth-month current | Sanming tonghui | books 2 and 5 |
| Natural pairs, teams, opposites and strains between animals | Sanming tonghui | books 2 and 3 |
| The twelve day qualities, and what each day suits | Xieji bianfang shu | books 4 and 10 |
| The almanac’s day spirits | Xieji bianfang shu | books 4 and 5 |
The Western sky
- Ptolemy, Tetrabiblos, second century AD: the qualities of the planets and the aspects between them, in J. M. Ashmand’s 1822 English translation of the Greek paraphrase attributed to Proclus, open at Project Gutenberg.
- William Lilly, Christian Astrology, London, 1647: Book I, on the aspects and on each planet when well and when ill placed, read from the page images of the Wellcome Collection’s copy, open at the Internet Archive.
- The planets are placed in the tropical zodiac, the one Western astrology commonly uses, with the same Astronomy Engine positions as the calendar.
How we use them
- Every rule names its passage. In the app’s code, each rule carries the passage it rests on, quoted in the original with its book, section and leaf, and is checked by at least one test.
- Our own words. The cards are written in English for Sixty Skies. Each one keeps three things apart: what the source says, how we read it today, and what the app suggests.
- Where sources differ, we say so. When classical writers disagree, the app keeps the choice as a named option instead of deciding silently. For example, the Sanming tonghui counts four “breaks” between animals and leaves out two pairs because they also combine, so the app uses those four.
- Within the tradition’s limits. The classical books also speak of fortune, illness and wealth. Sixty Skies leaves those out: it describes what a day supports and what it strains, and the decisions stay yours.