How MASTRO Computes the Sky.

Indian Vedic astrology operates on the Sidereal Zodiac (Nirayana), which accounts for the axial precession of the Earth (~50.29 arcseconds per year). The angular difference between the moving vernal equinox (Tropical) and the fixed star Spica (Chitra at 180°00′00″) is the Lahiri Ayanamsha:

At epoch J2000.0 (JD 2451545.0), Lahiri Ayanamsha was 23° 51′ 25.53″ (23.857092°). MASTRO integrates the IAU 2006 general precession polynomial and lunar nutation in longitude to guarantee arc-minute precision across all birth dates.

The Ascendant (Lagna) is the exact degree of the ecliptic rising over the eastern horizon at the observer’s geographical latitude (φ) and longitude (L). Derived from Local Sidereal Time (θ) and the true obliquity of the ecliptic (ε):

Because the ascendant shifts by roughly 1° every 4 minutes, birth minute accuracy is essential. Whole-sign houses (Rashi-Chakra) place the entire sign containing λ_asc as the 1st House.

The 120-year Vimshottari cycle is triggered by the Moon’s exact sidereal longitude within its birth Nakshatra (span: 13° 20′ = 800 arc-minutes). The remaining fraction determines the starting Mahadasha balance:

Sub-periods (Antardashas) and sub-sub-periods (Pratyantardashas) are evaluated proportionally down to the second using the Gregorian mean solar year of 365.2425 days.

Brihat Parashara Hora Shastra defines 8 classical dimensions evaluated from both partners’ Moon positions:

Unlike generic matchmakers that simply return 0 for Nadi or Bhakoot, MASTRO incorporates classical cancellation exceptions (same sign different nakshatras, same nakshatra different padas, and friendly planetary rulers).

Authentic Ba Zi does not use the Lunar New Year. The astrological Year Pillar commences strictly at Li Chun (立春, Start of Spring), when the Sun reaches ecliptic longitude 315°. The Month Pillar is determined by the 12 Solar Terms (Jie Qi), and the Hour Pillar is corrected by True Solar Time (TST) based on observer longitude.