What is Western sidereal astrology ?

There are two camps of thought among western astrologers about the "starting point", 0 degrees Aries, in the zodiac. Sidereal astrology believes that the starting point is at a particular fixed position in the background of stars, while tropical astrology (which is adopted by the majority of Western astrologers) believes that the starting point is when the position of the Sun against the background of stars coincides with the Northern hemisphere vernal equinox (i.e. when the Sun position against the heavens crosses over from the southern hemisphere to the northern hemisphere) each year. In effect, in most Western astrology the link between the zodiac sign and the sky constellation from which it takes its name has been broken, whereas in Sidereal astrology it remains of paramount importance.

As the Earth spins on its axis, it "wobbles" like a top, causing the vernal equinox to move gradually backwards against the star background, (a phenomenon known as the Precession of the equinoxes) at a rate of about 30 degrees (one Zodiacal sign length) every 2,160 years. Thus the two zodiacs would be aligned only once every 26,000 years and were aligned about 2,000 years ago when the zodiac was originally established.

This phenomenon gives us the conceptual basis for the Age of Aquarius, whose "dawning" coincides with the movement of the vernal equinox across the cusp from Pisces to Aquarius in the star background.