The ecliptic is the imaginary plane defined by Earth's orbit around the Sun. From Earth's perspective, it is the apparent yearly path the Sun traces across the celestial sphere against the background of stars, particularly through the constellations of the zodiac
. Key points about the ecliptic:
- It represents the orbital plane of Earth around the Sun and extends to include the orbits of the other planets, which lie close to this plane
- The Moon's orbit is also close to this plane, which is why eclipses occur only when the Moon crosses the ecliptic plane at certain points called nodes
- The ecliptic is inclined about 23.4° to the celestial equator due to Earth's axial tilt, an angle known as the obliquity of the ecliptic
- The points where the ecliptic intersects the celestial equator mark the equinoxes, and the Sun's position along the ecliptic is used in celestial coordinate systems
- The ecliptic passes through 13 constellations of the zodiac, and the Sun, Moon, and planets appear to move along this path in the sky
In summary, the ecliptic is both a fundamental reference plane in astronomy and the apparent path the Sun follows over the course of a year, closely associated with the zodiac constellations and the occurrence of eclipses
