How we compute
The ephemeris: NASA JPL DE440
Planet positions come from DE440, the planetary ephemeris published by NASA’s Jet Propulsion Laboratory and used for spacecraft navigation. Our engine reads the DE440 data directly rather than relying on approximate formulas.
From raw positions to what you would have seen
For each body, the engine works out the apparent position seen from Earth at your birth moment:
- converts your birth time to the timescale the ephemeris uses;
- corrects for light-time, because light from a planet left it minutes to hours earlier;
- applies stellar aberration, the small shift caused by Earth’s own motion;
- applies the Sun’s gravitational bending of light;
- precesses the result to the date and reports longitude along the ecliptic of that date.
We check these positions against JPL’s Horizons service, the reference NASA publishes for exactly this purpose.
Western and Vedic zodiacs
Western (tropical) astrology measures signs from the spring equinox. Vedic (sidereal) astrology measures them from the fixed stars. The equinox drifts against the stars by about one degree every 72 years, so the two zodiacs are now about 24° apart, and your Vedic signs usually sit one sign behind your Western ones. We use the Lahiri ayanamsa, the standard measure of that gap in Vedic astrology.
Birth time and place
Every place you search has a time zone from the IANA time zone database, so daylight saving and historical clock changes are applied to your birth time. If we cannot find a time zone for a place, we do not guess. The Rising sign (ascendant) changes about every two hours, so it needs a birth time; without one, we show only the results that do not depend on it.
Planetary periods
Vedic timing uses the Vimshottari dasha system: a 120-year cycle of planetary periods whose starting point is set by the Moon’s position among the 27 nakshatras (lunar mansions) at birth.
The Chinese calendar
A Chinese zodiac year starts at Lunar New Year, not on 1 January. We use a fixed table of Lunar New Year dates for 1901 to 2100, built from the Hong Kong Observatory’s official Gregorian–Lunar Calendar Conversion Tables (one table per year, published by the Hong Kong government). Animals and elements follow the traditional cycle of 10 heavenly stems and 12 earthly branches. Your birth date is used as you enter it, with no time zone conversion.
Engine version
- Engine version: 0.19.0
- Ephemeris kernel: de440
- Ayanamsa model: lahiri_swe_zero_epoch_iau1976_v1
- Validation tolerance: 0.00036 arcseconds
- Validation baseline: JPL Horizons
What these results are, and are not
The astronomy is precise. The readings that come from it are traditions of interpretation, offered for reflection. They are not predictions you should rely on for medical, legal, financial or relationship decisions.