Zodiac System
The difference between tropical and sidereal zodiacs, and what ayanamsa means.
The Zodiac System setting determines the fundamental reference frame used to define the positions of the 12 zodiac signs.
Tropical
The tropical zodiac anchors the start of Aries to the spring equinox (vernal point). Because it is based on the cycle of seasons - the equinoxes and solstices - the sign boundaries gradually drift away from the actual constellations over time.
The vast majority of Western astrology uses the tropical system, and it is the default in HOSHIDOU. Nearly all English-language astrology books and online resources assume tropical positions.
Sidereal
The sidereal zodiac is anchored to the actual positions of the fixed stars. It is the system used in Vedic astrology (Jyotish).
Unlike the tropical zodiac, sign definitions are locked to the stars and are not affected by the precession of the equinoxes. The same birth data will produce different sign placements in tropical versus sidereal.
What Is Ayanamsa
Ayanamsa is the angular difference between the tropical and sidereal zodiacs. Because the spring equinox point shifts gradually due to the precession of the Earth's axis, the gap between the two systems changes over time. The current difference is approximately 24 degrees.
When you select the sidereal system, HOSHIDOU uses the ayanamsa value to convert tropical positions into sidereal positions.
How to Switch
Open Settings and select the Zodiac System option. Choose Tropical or Sidereal and the change takes effect immediately on all charts.