Ecliptic longitude

The ecliptic is the apparent annual path of the Sun — Earth’s orbital plane projected on the sky. Natal work primarily uses ecliptic coordinates (coordinate-systems, ecliptic-and-equator).

Longitude and latitude

Ecliptic longitude (λ) — 0°–360° along the ecliptic from the tropical vernal equinox (0° Aries) in Western charts.
Ecliptic latitude (β) — distance north/south of the ecliptic. The Sun stays near β ≈ 0°; the Moon can reach roughly ±5°.

“Planet at 15° Leo” means tropical λ ≈ 135°: sign = floor(λ / 30), degree in sign = λ mod 30.

Relation to equator

Right ascension and declination describe the equator frame; λ and β describe the ecliptic. Conversion uses obliquity ε (obliquity).

Geographic lat/long ≠ ecliptic λ

Terrestrial latitude/longitude fix the observer on Earth. Chart angles arise where the local horizon and meridian meet the ecliptic (chart-angles, chart-points).

Tropical vs sidereal λ

The same VSOP tropical λ can be displayed sidereally by subtracting ayanamsa in calculate_sidereal (sidereal-vs-tropical).