Credits

Data and software credits.

SignWheel stands on published data and open software. Here is every piece of it, named.

Planetary positions

VSOP87. The planetary series used for the Sun (through the Earth's series) and Mercury to Neptune are from VSOP87, produced by the Bureau des Longitudes, Paris (Bretagnon and Francou). We use the series in a shortened form, keeping every term large enough to move a position by more than about half an arcsecond.

astronomia. The VSOP87 data files reach us through the astronomia JavaScript package (original work by Sonia Keys; maintained by commenthol and contributors), used under the MIT licence.

The Moon and Pluto. The Moon's position and Pluto's starting series use the compact algorithms published by Paul Schlyter in "How to compute planetary positions". Pluto's series carries a small correction fitted by us to NASA JPL reference values over the years 1920 to 2030.

Accuracy reference. Our numbers are checked against ephemerides produced by NASA's Jet Propulsion Laboratory (DE440, public domain data), read through the Skyfield library (MIT). The reference itself was cross-checked against the Swiss Ephemeris in our test harness. The Swiss Ephemeris is used only as a measuring reference in our own testing; none of its code or data is part of this site.

Time zones

Time zone rules come from the IANA Time Zone Database, as built into your browser. The database is in the public domain.

Birthplace data

Place data from GeoNames (www.geonames.org), used under the Creative Commons Attribution 4.0 licence (CC BY 4.0). The place picker searches about 172,000 populated places from the GeoNames cities file (every town and city over 1,000 people), with each place's coordinates and IANA time zone. A short starter list of about 230 major birthplaces, checked by hand for this project, is searched first; the GeoNames list is the full list behind it.

The rest

The chart mathematics for the rising sign, Midheaven and houses, the wheel drawing, the interpretation texts, and the design are our own work for SignWheel. Facts are not ours: planetary positions, dates, and place data are facts or third-party data used under the licences credited above.