The ecliptic is the orbital plane of the Earth around the Sun or, it is the circular path on the celestial sphere that the Sun appears to follow over the course of a year. It is called this because eclipses only occur when the Moon crosses this circle. Because Earth's rotational axis is not perpendicular to its orbital plane, Earth's equatorial plane is inclined to the ecliptic by 23.4°, which is the ‘obliquity of the ecliptic’.
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