The ecliptic is the Sun’s apparent yearly path across the celestial sphere as viewed from Earth. Geometrically, it reflects the plane of Earth’s orbit projected onto the sky. Ecliptic longitude measures position along that reference circle.
The Moon and planets appear near the ecliptic because the major bodies of the Solar System orbit in roughly similar planes, though not exactly on one line. Astronomical software can compute their ecliptic coordinates for a stated time, viewpoint, and coordinate frame.
Astrological zodiac systems map signs along the ecliptic. The coordinate is a calculated quantity; choosing a tropical or sidereal zodiac and assigning symbolic meaning are additional conventions. The ecliptic should not be confused with the celestial equator, which is Earth’s equator projected into the sky.
See astrology and astronomy for how Astrologican separates coordinate facts from reflective interpretation.
Sources and further reading
For the astronomical definition and coordinate terminology, see the official USNO glossary and the project’s methodology. Astrological sign meanings are outside that factual source boundary.