Vedic vs Western Astrology: Technical Calculation Differences

Zodiac Systems: Sidereal vs Tropical

The fundamental difference is the reference frame. Tropical zodiac (Western) measures from the vernal equinox point, which precesses ~50.3 arc-seconds per year. Sidereal zodiac (Vedic) measures from fixed stars. The difference between them is called ayanamsa — currently about 24.17 degrees (Lahiri ayanamsa, the Indian government standard).

This means a planet at 15 degrees Aries in tropical is at approximately 21 degrees Pisces in sidereal. For about 75% of people, their Vedic sun sign differs from their Western sun sign. This is why sun-sign horoscopes feel inaccurate to many Indians who read Western-based predictions.

House Systems

Western astrology primarily uses Placidus houses (unequal house sizes based on time to cross the meridian). Vedic astrology uses Whole Sign houses (each house = one complete sign, equal 30 degrees). KP astrology uses Placidus cusps with sub-lord analysis. These different house systems can place the same planet in different houses.

Aspect Rules

Western aspects are angular: conjunction (0 degrees), sextile (60), square (90), trine (120), opposition (180) — with orbs of 6-10 degrees. Vedic aspects (Drishti) are house-based: all planets aspect 7th house. Mars additionally aspects 4th and 8th. Jupiter aspects 5th and 9th. Saturn aspects 3rd and 10th. No orbs — either aspect exists or it does not.

Vedika API supports all three systems (Vedic, Western, KP) with complete isolation — zero cross-contamination of terms or calculations between systems.