glossary
terms
- tropical zodiac
- A zodiac system anchored to the equinoxes and solstices. 0° Aries begins at the vernal equinox regardless of which constellation occupies that region of sky. Used in modern Western astrology.
- sidereal zodiac
- A zodiac system anchored to fixed stars and constellations. Positions are measured against the actual stellar background. Used in Vedic astrology and approximated in stardrift's ancient chart frame.
- ayanamsa
- Sanskrit for "part of ayana" — the angular offset between tropical and sidereal longitudes. stardrift uses a linear Lahiri-style value of approximately 23.85° at J2000.0, increasing ~50.29 arcseconds per year. Sidereal longitude = tropical longitude − ayanamsa.
- precession (of the equinoxes)
- A slow wobble of Earth's rotational axis caused by gravitational forces from the Sun and Moon. The equinoxes shift westward through the constellations over a ~26,000-year cycle, causing tropical and sidereal frames to drift apart.
- ascendant (rising sign)
- The zodiac sign rising on the eastern horizon at the moment and place of birth. Changes sign approximately every two hours. Highly sensitive to birth time accuracy.
- midheaven (MC)
- The point where the ecliptic crosses the local meridian above the horizon. Associated with career, public life, and direction in many astrological traditions.
- ecliptic
- The apparent path of the Sun across the sky over a year, projected onto the celestial sphere. Planetary longitudes in astrology are measured along this circle.
- ephemeris
- A table (or algorithm) giving celestial positions at specific times. stardrift uses VSOP87 planetary theory via Astronomy Engine.
- whole sign houses
- A house system where each of the twelve signs equals one house, starting from the Ascendant sign. stardrift uses whole sign houses for chart wheel layout.