Two equal-sign coordinate systems
Both the tropical and sidereal zodiacs used in astrology divide the ecliptic into twelve equal 30-degree signs. These mathematical signs are not the same thing as the modern astronomical constellations, whose visible boundaries are unequal.
The tropical zodiac defines 0 degrees Aries from the March equinox and therefore remains aligned with the seasonal equinox-solstice framework. A sidereal zodiac keeps a chosen offset relative to a stellar reference. That offset is called an ayanamsha, and different sidereal traditions choose different values.
Why an offset exists
Earth's rotational axis slowly precesses. As a result, the equinox reference moves relative to the background stars over a cycle of roughly 26,000 years.
Modern sidereal ayanamshas are roughly 24 degrees for current dates, but the exact value depends on the date and chosen method. Because each sign spans 30 degrees, subtracting the offset often—but not always—moves a tropical longitude into the preceding sidereal sign.
What Zohvia calculates
Zohvia calculates tropical celestial longitudes with the astronomy-engine software library. Its sidereal model geometrically follows the Positional Astronomy Centre's published fixed-initial-point description: a tropical longitude of 23°15′ at 1956-03-21 00:00 UTC, carried as a fixed inertial direction into the requested date. Thirteen one-arcsecond values printed in PAC's 2026–27 Rashtriya Panchang are within two arcseconds under Zohvia's disclosed 00:00 IST interpretation of each undated-hour row.
This is Zohvia's implementation, not PAC source code, PAC approval, a licensed Swiss Ephemeris calculation, or proof that one ayanamsha is universal. It can differ near a boundary from another program using another model or time interpretation.
An exact entered birth time remains required. Time affects the ascendant and houses, and the Moon can cross a sign, nakshatra, or pada boundary during a day. Zohvia does not infer or rectify an unknown time.
Position is not proof of interpretation
A coordinate system can be defined and a celestial longitude can be calculated. That does not scientifically validate personality claims, compatibility meanings, timing claims, or forecasts attached to an astrological sign.
Zohvia uses the sidereal reference because it is the selected framework for its traditional chart and matching calculations—not because the product has shown sidereal astrology to be more predictive or objectively true.
Where nakshatras fit
Zohvia divides the sidereal ecliptic into 27 equal nakshatra segments of 13 degrees 20 minutes and assigns the calculated Moon longitude to one of them and one of four padas. Nakshatra names have cultural and ritual uses, but their personality and future meanings remain traditional symbolism.