Natal Chart Calculator

How It Works

A natal chart (or birth chart) maps the positions of the Sun, Moon, and planets along the ecliptic — the apparent path of the Sun across the sky — at the exact moment of birth. The ecliptic is divided into twelve 30° segments called the zodiac signs. Each planet's position in a sign is interpreted in terms of that sign's element (Fire, Earth, Air, or Water) and modality (Cardinal, Fixed, or Mutable).

Sun sign is determined by the Sun's ecliptic longitude — calculated from Meeus's solar position formula using the mean longitude, mean anomaly, and equation of the center. It changes roughly once a month as Earth orbits the Sun.

Moon sign requires your birth time because the Moon moves ~13° per day — crossing a sign roughly every 2.5 days. Lunar longitude is computed from 30 perturbation terms (Meeus Chapter 47), including the key gravitational influences of the Sun (evection, variation, annual equation), giving accuracy to ~0.1°.

Rising sign (Ascendant) is the zodiac sign rising over the eastern horizon at birth. It requires both birth time and location because it depends on Local Sidereal Time — Earth's rotational angle relative to the stars. The Ascendant shifts by roughly 1° every 4 minutes, cycling through all 12 signs in ~24 hours. Whole Sign houses are used here: the Rising sign occupies the entire 1st house, and each subsequent sign is the next house.

Planet positions are computed from mean orbital elements (semi-major axis, eccentricity, mean longitude, and perihelion longitude) via Kepler's equation. The geocentric ecliptic longitude is derived by subtracting Earth's heliocentric position from the planet's heliocentric position. Accuracy is approximately ±1° for inner planets and ±0.5° for outer planets over dates within a few centuries of J2000.0 (January 1, 2000).

Astrology is for entertainment and self-reflection only. Planetary positions are astronomical facts; their astrological interpretations are a cultural tradition, not empirical science.