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Taoist Calendar
Taoist practice keeps time by the Chinese calendar. Ten heavenly stems and twelve earthly branches pair off into a cycle of sixty that names every year, month, day and double hour; twenty-four solar terms mark the Sun's road in steps of fifteen degrees; and the lunar months run from new moon to new moon. The calendar reads all three for your place and moment, draws the year as a wheel, and keeps a note of the day if you wish.
A study instrument. It computes the lunar calendar and the solar terms by the rules of the Chinese standard, GB/T 33661-2017, and the Four Pillars by traditional rules, which the instrument names; it does not tell fortunes or choose days, and where the traditions keep different conventions it names them and lets you choose.
Setting the calendar to your time and place
The tradition
The Chinese calendar names time with two cycles laid together. The ten heavenly stems (tiāngān 天干) and the twelve earthly branches (dìzhī 地支) pair off into a cycle of sixty, already used to count days on the Shang oracle bones; the count of days has run without a break since at least the eighth century BC. The same cycle came to name the years from the first century AD, and the months and double hours by rule; from the Tang and Song the four together, the year, month, day and hour of a birth, became the Four Pillars (sìzhù 四柱), the eight characters (bāzì 八字) of the ziping art of fate.
The Sun's year is divided into twenty-four terms (èrshísì jiéqì 二十四節氣), listed complete in the Huainanzi of 139 BC, and the months run from new moon to new moon. Until the seventeenth century the terms were equal slices of the year (píngqì 平氣); the Shixian calendar of 1645, made with the Jesuit astronomers at the Qing court, set each term where the Sun's apparent longitude reaches a multiple of fifteen degrees (dìngqì 定氣), and kept the old rule that a month holding no principal term is the leap month. Since 1929 the calendar has been reckoned for the meridian of 120° east, and since 2017 its rules have stood as a national standard, GB/T 33661-2017.
Reading the instrument
- The Four Pillars read the instant for the year and month, and your place's clock for the day and hour. The year turns at the Start of Spring (立春, the Sun at 315°), the month at each of the twelve sectional terms (節), the day at midnight or, if you choose, at 23:00, and the hour every two hours from 23:00. Month stems follow the five-tigers rule, hour stems the five-rats rule.
- The lunar date is the Chinese calendar's date for your place's calendar day, reckoned, as the standard requires, in China Standard Time (UTC+8) wherever you are: a month begins on the day of the new moon in Beijing, the month holding the winter solstice is the eleventh, and when thirteen months run from one eleventh month to the next, the first of them with no principal term is the leap month. The festival year and its animal turn at the lunar new year, the pillars' year at 立春; the instrument shows both.
- The wheel sets the year south at the crown, midsummer above and midwinter below, running clockwise: the twenty-four terms and their seventy-two pentads on the rim, the twelve months of the pillars within, and the lunar months nearest now at the centre. Touch a term, a month or a pillar to open it.
- Terms and new moons come from the Sun's and Moon's apparent longitudes to within about a minute, or two late in the century, as far as the Earth's rotation can be forecast. Against the Hong Kong Observatory's tables for 1901 to 2100, every month and term date agrees from 1929; before 1929 the instrument keeps as published the three months the calendars of the time began a day earlier. A new moon within one to three minutes of Beijing midnight (wider for later years) is marked as too close to settle; a term that close to midnight on your clock carries a note that calendars may print it on either day.
- Solar time, if chosen, is the Sun's own time at your longitude, the equation of time included; it moves the day and hour pillars and nothing else. The pentads are placed at every five degrees of the Sun, a third of each term; almanacs that count five days from the term may differ by a day. The hour opens in the Organ Clock, and the phase of any stem or branch in the Five Phases Wheel.
Where it descends from
- GB/T 33661-2017, 農曆的編算和頒行
- The national standard for calculating and promulgating the Chinese calendar: Beijing time, the new-moon day, the eleventh month at the winter solstice and the leap-month rule this calendar follows.
- Huainanzi 淮南子, chapter 3, Tianwen
- The earliest complete list of the twenty-four terms, with the stems and branches set to the phases and directions.
- Xiyang xinfa lishu 西洋新法曆書
- The treatise of the new Western method that Adam Schall von Bell presented in 1645, behind the Shixian calendar and its true-Sun terms.
- Yueling qishi'er hou jijie 月令七十二候集解
- Wu Cheng's Yuan commentary on the seventy-two pentads of the Monthly Ordinances, whose wording the calendar follows.
- Sanming tonghui 三命通會
- Wan Minying's Ming compendium of the Four Pillars, with the rules for the month and hour stems.
- Astronomical Algorithms
- Jean Meeus's handbook (2nd ed. 1998): the Sun, the Moon and sidereal time behind every term, new moon and solar hour; ΔT follows Espenak and Meeus's polynomials (NASA, 2006).
- The Mathematics of the Chinese Calendar
- Helmer Aslaksen's clear account of the modern rules, the leap month and the difficulty of 2033.
- Gregorian–Lunar Calendar Conversion Tables
- The Hong Kong Observatory's tables for 1901 to 2100, against which every month and term of this calendar was checked.
What this does not claim
A study calendar. It computes the calendar and the Four Pillars by the conventions named on it, and reads nothing from them: it does not tell fortunes or choose days, and claims no effect of stems, branches or phases on health, character or events. Conventions differ, and the instrument names its choices; some schools turn the day at 23:00 or reckon the hours by solar time, and both are offered here as choices; some reverse the months in the southern hemisphere, which this calendar does not. Korean and Vietnamese lunar calendars, reckoned at UTC+9 and UTC+7, sometimes begin a month a day apart from the Chinese, and in 1985 Vietnam kept its new year a month before China. The pentads describe the seasons of the Yellow River plain, and some of their signs are old beliefs about transformation.
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