How it works

Two Skies calculates your Western birth chart and your BaZi chart from the same birth moment, then compares them with fixed rules. An AI model writes only the paid reports.

The Western chart

Planet positions come from Astronomy Engine, an open-source astronomy library. We use the tropical zodiac and whole-sign houses. Your clock time is converted to universal time with the time-zone history for your birth place, including daylight saving and old local time.

The BaZi chart

Your four pillars come from lunar-javascript, using solar terms and true solar time: your clock time corrected for your longitude and the equation of time, because the classical texts count hours by the sun. Near an hour boundary this can change your hour pillar, and we tell you when it does. A birth after 23:00 by the sun counts toward the next day's pillar.

How the comparison works

For the West, we weight your Sun and Moon at 3 points each, your rising sign at 2, and Mercury, Venus and Mars at 1 each, then take the leading element. A tie goes to your Sun's element. For the East, we use your day master's element.

The two systems don't share a list of elements, so we map fire, earth and water straight across, and read air as wood. The Book of Changes places wind and wood in one trigram (巽). Metal has no Western counterpart. Then we apply the five-element cycle: same element, one feeding the other, or one checking the other. About one chart in five comes out with both systems agreeing. We got that figure from 4,000 simulated birth moments.

Compatibility and love

For two people, the East compares year animals, day masters, day branches, year sounds (納音) and the five elements, by the classical tables of combinations and clashes. The West takes the angles between the two charts' Sun, Moon, Venus, Mars and Saturn. For one person, the East reads the day branch, the partner star, the peach blossom (桃花) and the red star (紅鸞), and the West reads Venus, Mars, the Moon and the 7th house. We don't give a score, and nothing here says what will happen.

The tarot draw

Three cards are drawn at random in your browser, each upright or reversed. The three positions come from the ten-card method in A. E. Waite's The Pictorial Key to the Tarot, which he calls the most suitable for a definite question. We use his first two and his sixth. The card pictures are the 1909 deck drawn by Pamela Colman Smith, not any later recoloured edition.

The I Ching coin chart

Six tosses of three coins give six lines. Each line gets a branch, a relative, a spirit and a place as the Self or the Other line, by the rules in Zeng Shan Bu Yi (增刪卜易). Our code reproduces that book's printed table of all 64 hexagrams, apart from six misprints in the copy we use, which we checked against the same book's rule list. The month and day come from lunar-javascript.

The Zi Wei Dou Shu chart

The twelve palaces and the stars come from iztro, an open-source library. We checked the Life palace, Body palace, the fourteen major stars and the four transformations against the rules printed in Zi Wei Dou Shu Quan Shu (紫微斗數全書), over 400 births. Where the library and the book differ on the transformations, in years with the stem 壬, we follow the book. The hour comes from true solar time, as for BaZi.

What the AI does

Free results use text we wrote in advance, chosen by those rules. The paid reports are written by an AI model (Claude, from Anthropic) from the chart facts. It is told to rest every section on a named placement, and to stay away from predictions about health, death, pregnancy, law or money. It can still get things wrong.

How the quotations work

The AI can only name a passage from a list we give it. Our code then prints the original, the English, the book, the chapter and a link. We checked each passage character for character against the saved text of its book. If the AI writes out a quotation of its own that doesn't match, our code removes it. We don't quote passages about illness, death, pregnancy, lawsuits or getting rich, though the old books have plenty. A quotation shows what an old book says and proves nothing.

Sources

Chinese texts are from Chinese Wikisource, with our own English: Zhou Yi (周易), Zeng Shan Bu Yi (增刪卜易), Huo Zhu Lin (火珠林), Jing Shi Yi Zhuan (京氏易傳), Zi Wei Dou Shu Quan Shu (紫微斗數全書), Di Tian Sui (滴天髓), Yuan Hai Zi Ping (淵海子平), San Ming Tong Hui (三命通會) and Shen Feng Tong Kao (神峰通考). Old copies have misprints and we quote what the copy says, except that three misprints in the Di Tian Sui verses are corrected against the common printed version. Western passages are from Project Gutenberg: Ptolemy's Tetrabiblos in J. M. Ashmand's translation, and Sepharial's Astrology: How to Make and Read Your Own Horoscope. Tarot passages are from Waite's book on English Wikisource, and the card pictures from Wikimedia Commons. Birth data for example charts is from Astro-Databank, graded AA or A only. City and coordinate data is from GeoNames (CC BY 4.0).

What this is not

Neither astrology, BaZi, the I Ching, Zi Wei Dou Shu nor tarot has scientific support as a way of predicting anything. We treat them as old and interesting ways of describing a person or a moment, and as a prompt for thinking for yourself. Please don't use this site to decide anything important.