What phenomenon causes the zero points for celestial longitude (the equinoxes) to shift westward along the ecliptic over long periods?
Answer
Precession
Precession is the slow, ongoing wobble of the Earth's axis, which causes the entire celestial coordinate system, including the position of the equinoxes, to drift slowly westward relative to the fixed background stars over centuries.
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The Ecliptic: Crash Course Kids #37.2 - YouTube
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