Ecliptic
The ecliptic is the apparent annual path of the Sun across the celestial sphere, corresponding to the plane of Earth’s orbit around the Sun.
Earth's orbit: Earth’s yearly revolution around the Sun, which defines the plane of the ecliptic. The ecliptic traces the direction of Earth’s orbital plane against the distant stars.
Celestial equator: The projection of Earth's equator onto the celestial sphere. Its tilt relative to the ecliptic sets the Sun’s annual north–south motion.
Astronomical coordinate system: A framework for specifying the positions of objects on the celestial sphere. The ecliptic supplies the reference plane for one widely used coordinate system.
Lunar orbit: The path of the Moon as it orbits Earth. Its plane is inclined to the ecliptic, so the Moon does not remain exactly on the Sun’s apparent path.
Celestial sphere: An imaginary sphere centered on an observer, used to map the apparent positions of celestial objects. The ecliptic is a circle drawn across this apparent sky.
Ecliptic plane: The plane of Earth’s orbit around the Sun, extended indefinitely through space. This physical plane is the geometric basis of the ecliptic’s apparent path.
Solar eclipse: An event in which the Moon passes between Earth and the Sun and obscures the Sun. A solar eclipse occurs near an intersection of the Moon’s orbit with the ecliptic.
Planetary orbit: The path a planet follows around a star under gravitational influence. Other planets orbit in planes close to, but not identical with, Earth’s orbital plane.
Axial tilt: The angle between a rotating body's spin axis and a chosen orbital or reference axis. Earth’s tilt relative to its orbital plane produces the seasons, though it does not define the ecliptic.
Zodiac: A belt of the sky centered on the ecliptic, traditionally divided into twelve signs. The Sun, Moon, and planets appear within this belt as seen from Earth.