The ecliptic is the apparent path that the Sun follows through the sky over the course of a year as seen from Earth. This path is a reflection of Earth’s orbit around the Sun. More specifically, the ecliptic is the projection of Earth’s orbital plane onto the celestial sphere.
Why is the Ecliptic Important?
- Defines the Zodiac – The twelve zodiac constellations lie along the ecliptic, and historically, they played a key role in astrology and early astronomy.
- Determines the Seasons – The tilt of Earth’s axis (about 23.5° relative to the ecliptic) causes the Sun’s position along the ecliptic to vary, leading to the changing seasons.
- Moon and Planetary Motion – The Moon and planets also move close to the ecliptic because the Solar System’s planets orbit in roughly the same plane.
- Eclipses Occur Along It – Solar and lunar eclipses happen only when the Moon crosses the ecliptic at points called nodes, aligning with the Sun.
- Reference for Celestial Coordinates – The ecliptic is used as a fundamental reference in astronomy, with celestial longitude and latitude measured relative to it.