DRAFT

Method & Sources

The rules behind Lunabao’s charts and tarot draws.

Birth time and place

Everything starts from the clock time at the birthplace. We find the place’s historical time zone and daylight-saving rules in the IANA time zone database, using the date you give, not today’s rules and not the time zone of your device or of our server. If a clock time was repeated or skipped when daylight saving changed, we ask which one you mean.

Local standard time, with any daylight-saving offset removed, is the default for choosing the Zi Wei hour. We also calculate true solar time, which is the standard time plus a correction for how far the birthplace is from the centre of its time zone, plus the equation of time. When the two clocks fall in different two-hour periods, we flag a birth time near a boundary and offer the choice. The default stays local standard time.

City search uses a built-in list of about 26,000 places, so smaller towns abroad may be missing. Pick the nearest listed city; within one time zone, each degree of longitude moves true solar time by 4 minutes. For some European zones, time zone history before 1970 follows a merged zone, so very old births there can be off by local differences.

If the birth time is unknown we keep it unknown. We do not guess a time. Charts show only what that day allows, and the page says what is missing.

Sources

IANA Time Zone Database (public domain)
GeoNames place data (CC BY 4.0)

Zi Wei Dou Shu

Zi Wei charts use iztro’s default calculation settings, with US English output and the Chinese lunar calendar. The lunar year starts on the first day of the first lunar month. This is one school of Zi Wei among several, and we do not claim it is the only correct one.

We convert the clock time at the birthplace to local standard time by removing any daylight-saving offset. We use that time to find the shichen, a two-hour period used in Zi Wei. We also calculate true solar time. If the two clocks fall in different shichen, we flag the boundary and offer a choice. Local standard time is the default.

Two calendar edge cases follow iztro’s defaults. In a leap lunar month, days 1–15 count as that month and days 16 onward count as the next month. A birth from 23:00 to 23:59, the late Zi period, counts as the early Zi period of the next day. We apply that to the whole date, so at the end of a lunar month or year the chart moves into the new month or year. Other Zi Wei sites choose differently on both points, so a chart on another site may differ for births in the second half of a leap month or in the late Zi hour.

When birth time is unknown, the Zi Wei palace chart is unavailable. We show the information that can be determined from the year and offer a way to add the birth time.

Sources

iztro (MIT)
Hong Kong Observatory lunar calendar tables (used to check lunar dates)

Western astrology

We use Astronomy Engine and the tropical zodiac. Planet positions are the apparent positions seen from the Earth. We calculate Placidus houses by default. At latitudes more than 66° north or south of the equator, we switch to Whole Sign houses and show that change in the chart.

The North Node is the true node, calculated from the Moon’s actual orbit at that moment. Many astrology sites default to the mean node, a smoothed average, and the two can differ by 1–2°. If your node sign or degree looks different on another site, this is the first thing to check.

We show the five major aspects: conjunction, sextile, square, trine and opposition. Orbs are 8°, 5°, 7°, 7° and 8°, and 2° wider when the Sun or the Moon is involved. The nodes have no aspects.

Without a birth time, the Rising sign and houses are unavailable. If the Moon could have been in either of two signs that day, we show both possibilities. Without a birth city, the time zone is unknown too, so we check every moment that date could mean anywhere on Earth and show both signs for any body that changes sign in that window.

Sources

Astronomy Engine (MIT)

Chinese zodiac

For the zodiac identity card, the animal year changes at Chinese New Year, also called Spring Festival. Birthdays before that date are still in the preceding zodiac year. Births within a day of the date are flagged, because the date is a date in China and can be read either way elsewhere.

The element beside the animal (for example Fire Horse) comes from the same Chinese year. Our table of Chinese New Year dates covers 1900–2100.

Sources

Hong Kong Observatory lunar calendar tables (used to check the dates)

Tarot

Our 78-card deck uses a secure random source and an unbiased shuffle. A card appears at most once in a deal. Each drawn card has a 50% chance of appearing upright and a 50% chance of appearing reversed. A saved draw is reused when you return to it, so the daily card stays the same all day on that device.

The deck uses public-domain scans of the original 1909 artwork by Pamela Colman Smith. Our English card meanings start from Waite’s 1910 book and are written for Lunabao as modern, plain-English readings for reflection. Where his old wording is grim, we soften it or take a lighter reading, so these are not his words or a claim about what any card must mean.

Sources

Pamela Colman Smith’s original 1909 tarot artwork (scans on Wikimedia Commons)
Waite, The Pictorial Key to the Tarot (1910)

What we checked

We checked that the software follows the rules above, and we report what was and was not covered. Chinese New Year dates matched the Hong Kong Observatory tables for all 200 years from 1901 to 2100. Planet positions for 10 test cases matched NASA/JPL Horizons within 17.4 arcseconds at most. For Rising sign, Midheaven and house cusps, three full charts matched one public website that displays results to one arcminute, within 0.41 arcminutes for cusps and 0.61 arcminutes for planets.

For Zi Wei we compared 30 made-up birth details with two public Chinese charting websites, china95.net and k366.com, plus the Hong Kong Observatory lunar calendar and a small rule-based calculation of our own. The main fields (life palace, body palace, five-element class, major stars in the twelve palaces and the birth-year transformations) agreed across all three in 25 of 30 cases. The other 5 are differences in school, in how a leap month and the late Zi hour are handled, not errors on either side. Lunar dates matched the Observatory in 30 of 30. The comparison was done by AI, not by a human Zi Wei practitioner.

Limits: house positions were compared against only one public website, which does not publish its method, so it is not fully independent of ours. We did not compare against the other professional astrology programs. Boundary cases, places missing from the city list, and births before 1970 in some European zones are where you are most likely to see differences from other sites.

Software that calculates correctly does not mean astrology or tarot can predict anything. Lunabao is entertainment and self-reflection, and the Disclaimer applies to everything here.

Sources

Hong Kong Observatory lunar calendar tables
NASA/JPL Horizons
china95.net Zi Wei chart calculator
k366.com Zi Wei chart calculator
astro-charts.com natal chart

How interpretations are written and labelled

The chart facts are calculated by software. The explanations beside them come from a library of prepared texts. Nothing is written by AI while you use the site, and the free pages call no AI service.

The texts were drafted with AI assistance. Each passes automatic checks (length, sources present, and a list of banned fear, medical, financial, legal and guarantee wording) and an independent review against a checklist. The site owner then reads a translated sample of each batch, not every line. A batch goes live only after it is marked approved. No professional astrologer or Zi Wei practitioner has reviewed these texts yet. An agreement between AI tools is not treated as proof of a fact, and a source counts only if we actually found and read the passage.

Every text carries one of four labels. Documented history means a fact with a source we can point to. Traditional attribution or legend means something a classical text or tradition says, not something we claim is true. Symbolic interpretation is a reading of a symbol. Modern entertainment is our own writing for fun. A tradition-based claim without a findable source is labelled symbolic or modern entertainment instead.

East and West are matched by theme (Self, Love, Career, Money, Family, Friends, Growth). When both sides show the same quality we say so; when they do not, we say they are two different angles, and we do not force a match.

Sources and credits

These are the sources our interpretation texts cite, as recorded when we read them on 2026-11-05. Only short phrases and paraphrase are used. Everything else in the library is our own writing and is labelled that way.

Open-source software and data: iztro (MIT), Astronomy Engine (MIT), the IANA Time Zone Database (public domain), and GeoNames place data © GeoNames (geonames.org), CC BY 4.0. Tarot images are 1909 public-domain scans.

Sources

Zi Wei Dou Shu Quan Shu (紫微斗數全書), Book 1 and Book 2, Chinese Wikisource transcription (public domain)
Lunheng (論衡), chapter 14 Wushi, by Wang Chong, Chinese Wikisource transcription (public domain)
Waite, The Pictorial Key to the Tarot (1910), reference for our own card meanings
iztro, MIT licence
Astronomy Engine, MIT licence
IANA Time Zone Database, public domain
Pamela Colman Smith’s 1909 tarot artwork, public domain