The Mathematics of the Longitude - Department of Mathematics

Figure 2.4
2.3 Other Reference Markers on the Celestial Sphere
The earth orbits the sun in a plane called the ecliptic (Figure 2.5). From
our vantage point, however, it appears that the sun circle us once a year in
that same plane. Hence, the ecliptic may be alternately defined as "the
apparent path of the sun on the celestial sphere".
Figure 2.5 Earth orbits the sun in an ecliptic plane.
The ecliptic is tilted 23.5 degrees with respect to the celestial equator
because the earth's rotation axis is tilted by 23.5 degrees with respect to its
orbital plane. Be sure to keep distinct in your mind the difference between
the slow drift of the sun along the ecliptic during the year and the fast
motion of the rising and setting sun during a day.