Caption: The Sun's path on the sky on a day of an equinox for a location in the Northern Hemisphere.
The celestial sphere ITSELF is the tilted sphere in the image.
Features:
To understand this, note that on the horizon plane (i.e., on the ground), the due east-due west line is perpendicular to the due north-due south line (i.e., the projection onto the horizon plane of the celestial axis). Thus the due east-due west line is perpendicular to the celestial axis and thus intersects the celestial equator.