This takes as a point of reference the diurnal rotation of the Earth around its axis. Extending the North and South poles, you have the North and South Celestial poles. Extending the Equator, you have the Celestial Equator. The Equator is intercepted by Hour Circles, whereby location is indicated in hours and minutes of Right Ascension, measured Eastward from the Zero Circle which passes through Greenwich. Parallel to the Equator are Parallels of Declination, indicated by their angular distance plus, if North of the Equator; and minus if South.
With your celestial sphere marked off on this system, it can be seen that the Sun does not travel around this Celestial equator; but instead, its orbit is inclined to that of the Equator some 23.5 degrees. The points at which the Sun's apparent orbit intersects the Equator are the Equinoxes, and the points of greatest separation are the Solstices. (These names have to do with an entirely different but coincidental factor. v. Precession.)
