University of California
Cse: What's Your Sign? The Science Behind the Zodiac
This paper presents the explanation behind the Zodiac signs. It discusses motions of celestial objects, the Plane of the Ecliptic, and the constellations of the Zodiac.
Other
Autumnal Equinox From the Electronic Sky
This site, written by an amateur astronomer with 30 years of study and interest, explains the equinox with photos and charts.