A calculator based on the sidereal zodiac provides planetary positions as measured against the backdrop of fixed stars. Unlike tropical astrology, which uses the vernal equinox as its starting point, sidereal calculations align with the constellations themselves. For example, if the Sun is in the constellation of Aries according to sidereal measurements, it will appear within that constellation in the sky.
This approach emphasizes astronomical observation as the foundation of astrological interpretation. By accurately reflecting the celestial positions of planets relative to the stars, this method aims for greater precision in mapping planetary influences and cycles. Proponents suggest this historically rooted approach offers a more accurate understanding of astrological phenomena.