How Zodiux computes your chart

Real astronomy, one source

Every position on this site — your birth chart, the live sky strip, the Mercury retrograde tracker — comes from Astronomy Engine, an open-source implementation of the VSOP87 and NOVAS algorithms. The same library is bundled into the page you are reading and into the build that generates these pages, so the sky quoted on a sign page and the sky in the calculator cannot disagree.

We report geocentric apparent ecliptic longitude: where a body appears along the zodiac from the centre of the Earth, corrected for light-travel time and aberration.

Which build. The library ships no version string, so rather than quote a number we cannot verify, here are the exact bytes this site runs. Hash the files yourself and compare:

Upstream is MIT-licensed, copyright Don Cross 2019–2023. If these fingerprints change, the ephemeris changed, and that is the thing worth watching — not a version number nobody can check.

Tropical, twelve equal signs

Zodiux uses the tropical zodiac: twelve equal 30° divisions measured from 0° Aries, the point of the March equinox. This is the convention Western astrology has used for two thousand years. It is not the sidereal zodiac used in Vedic astrology, which is currently offset by roughly 24° — if you have a Vedic chart, expect different signs.

Your rising sign is the zodiac degree climbing over the eastern horizon at your birth moment, derived from local sidereal time at your birth longitude. The free chart gives you sun, moon, rising and every planet by sign. It does not draw house cusps, so it takes no position on Placidus versus Whole Sign versus Koch — a choice that changes results and that we would rather make explicit than silently.

Where the error actually lives

Your birth city carries its own time zone in a bundled dataset of about 36,000 cities. Your wall-clock birth time is converted to UTC through that zone before any astronomy runs, using your browser's own historical time-zone database.

That database is where practical error concentrates. Births before 1970, and places that shifted their standard offset or ran irregular daylight saving, are the realistic sources of a one-hour mistake — not the planetary maths. An hour moves the Moon under half a degree, but it moves the rising sign by roughly half a sign.

No birth time? We assume local noon and say so on the result. Sun and the outer planets stay reliable. The rising sign is omitted rather than guessed.

What we round, and why it doesn't matter

Positions are accurate to well under a degree for any modern birth date — orders of magnitude finer than the 30° sign boundaries the readings are built on. One simplification is worth naming: the obliquity of the ecliptic is held at a fixed 23.4367°, its approximate value for 2026, in the rising-sign calculation. Obliquity drifts by about 0.013° per century, so this is worth a fraction of an arcminute today. It is visible only if you were born within seconds of a sign boundary — and if you were, no calculator on the internet can settle it without a birth certificate time to the minute.

How the writing is made

Interpretations are written by the Zodiux editorial team against a fixed brief: describe the traditional meaning of a placement, in plain language, without flattery and without prediction. We do not generate readings that claim to know your future, your medical situation, or your relationships. Sign and compatibility pages are reviewed when the underlying astronomy changes and on a rolling schedule otherwise; the date on each page reflects its own last substantive edit, not a site-wide batch stamp.

Everything here is for reflection and entertainment. It is not advice — not medical, legal, financial or psychological. Compatibility scores describe traditional element and modality relationships between two signs. They are not a prediction about two people.

Your birth data stays on your device

The free birth chart and compatibility tools run entirely in your browser. Your birth date, time and city are never sent to us, and since August 2026 they are not written into the page URL either — a link only carries them if you press Copy link to this chart yourself.

A paid report is the one exception, and a deliberate one: the report is rendered on the server, so those details are transmitted and kept for up to 30 days. The Reports page states this before payment, and the privacy policy covers the rest.