Ephemeris and astronomical source
We implement the core algorithms from Jean Meeus, Astronomical Algorithms, 2nd edition. This includes solar theory (chapter 25), lunar periodic terms (chapter 47), obliquity, sidereal time and planetary mean elements. The results are cross-checked against Swiss Ephemeris values to ensure consistency.
House and zodiac system
Calculations use the tropical zodiac, aligned with the seasons and the vernal equinox. House cusps are not required for Sun, Moon or rising sign calculations; if a full chart is generated, Placidus is the default house system.
Time zones, daylight saving and historical time
We use the IANA time zone database through the Intl API. Birth date and time are converted from local civil time to Universal Time before the ephemeris is evaluated. Historical daylight saving and war-time changes are handled by the browser or server Intl implementation.
Rising sign and birth time uncertainty
The Ascendant changes roughly every two hours as the Earth rotates. Without an exact birth time the rising sign cannot be determined reliably. We always show a clear warning when the birth time is missing or approximate.
Privacy and data handling
Free calculator inputs are used only to produce the result and are not stored on our servers. No birth data is retained after the response is sent. See our full Privacy Policy for more details.
Sources
- Meeus, Jean. Astronomical Algorithms, 2nd edition. Willmann-Bell, 1998.
- Swiss Ephemeris, Astrodienst. https://www.astro.com/swisseph/