The geometry of annual apparent motion
Earth’s solar orbit produces the Sun’s annual change of direction against the stellar background. Projecting the orbital plane onto the celestial sphere defines the ecliptic great circle.
This is viewing geometry, not a physical ring on which the Sun revolves around Earth. Geocentric apparent directions are compatible with a heliocentric orbital explanation.
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The ecliptic and equator
The ecliptic and celestial equator intersect at about 23.4 degrees. Their crossings define the equinox directions where the Sun passes from one side of the equator to the other.
Solar position relates to seasons, but the hemispheres have opposite seasons. Northern spring terminology does not mean every observing location enters spring at the same geometric event.
A reference for Solar System directions
Major planetary orbits lie near Earth’s orbital plane, placing familiar planets near the ecliptic. Their inclinations, and the Moon’s, still differ; they do not all remain on one exact line.
Horizons distinguishes heliocentric from observer-centered ecliptic coordinates and specifies reference planes. Comparisons require their centers and date conventions, rather than interchanging ecliptic, equator and local horizon.