What physical phenomenon is responsible for the discrepancy between the tropical and sidereal zodiacs?

Answer

The precession of the equinoxes, a slow wobble in the Earth's rotation axis.

The discrepancy noted between the tropical zodiac, which is tied directly to the equinoxes (the intersection points of the ecliptic and celestial equator), and the sidereal zodiac, which attempts to align with the fixed patterns of the distant stars, is caused by the precession of the equinoxes. This phenomenon describes a very slow, long-term nodding or wobbling motion of the Earth's rotation axis. Because the equinoxes are defined by this moving axis/orbital plane intersection, they slowly drift westward relative to the background stars over millennia. Consequently, the point marking the start of spring (the vernal equinox) no longer aligns with the same constellation it did when the initial calendrical and astrological systems were first established, leading to the growing offset between the two zodiac systems.

What physical phenomenon is responsible for the discrepancy between the tropical and sidereal zodiacs?

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