What is the primary reason the Sun's path varies so dramatically between summer and winter?

Answer

The axial tilt of the Earth, approximately 23.5 degrees

The Earth's axial tilt of approximately 23.5 degrees dictates the Sun's declination, causing the path in the sky to shift significantly north in summer and south in winter in the Northern Hemisphere.

What is the primary reason the Sun's path varies so dramatically between summer and winter?
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