Astrology 101 – A Zodiac Explanation
An area of confusion amongst inexperienced astrologers and those totally ignorant of how astrology is practiced is the difference amongst tropical signs, sidereal signs and constellations.
Heres an overview:
Tropical Zodiac Is 12-fold division of the Ecliptic (the apparent path of the Sun around the Earth) which starts with the Vernal Equinox as 0 degrees Aries with each sign having 30 degrees - used in Western Tropical astrology.
Sidereal Zodiac Is 12-fold division of the Ecliptic based on an ayanamsa value as the projected from the Vernal Equinox for the 0 Aries point to supposedly correct for precession, each sign having 30 degrees. These are mostly used in Vedic astrology, also known as Jyotish. There are several ayanamsas currently in use by different schools of Vedic astrological thought, such as Lahiri ( the official Indian government ayanamsa), the Fagan-Bradley, the Rahman, and the Khrisnamurti. All of these are around 24 degrees forward of the Vernal Equinox. Thus, someone who has the Sun placed at 1 degree Aries in the Tropical Zodiac, the Vedic position would be 6 degrees Pisces.
Constellations The zodiacal constellations do not really have specific, completely agreed upon boundaries. They are not each 30 degrees in length. Most astrologers (except for some Western Siderealists) do not use the constellations to measure planetary movement. Due to precession, the constellations do not correspond with the Tropical Zodiac, nor do the constellations fit into Sidereal Signs due to the inexact and varied size of the constellations. Astrology debunkers frequently set up a Straw Man argument about this because they dont know how astrology is really practiced.
One must realize that no one of these ways of measuring planetary positions against the background of the Ecliptic is correct or incorrect - they are just different ways of measuring the same thing. They all describe the 360 degrees of the Ecliptic. One may use different tools or markers an objects length, the length itself remains the same. Just as 4 inches equals 10.16 centimeters equals 1 hand, its all the same length - just a different measuring system.