Updated: Dec 3, 2020
The difference between the well known system of Tropical Astrology, popularized as the main system of western astrology around the world through newspapers and websites, and Sidereal Astrology, based in astronomical observation is significant and often overlooked (Vedic Astrology also uses this Sidereal zodiac). Tropical Astrology makes use of the Tropical zodiac, devised over 2000 years ago as the same science as Astronomy in cultures like Babylon and Egypt. In this system the suns position at the the vernal equinox was always the first degree of the sign Aries (all signs being an equal 30 degrees), the start of Sun in Aries marking the beginning of the Spring season. Sidereal Astrology originates in modern astronomical observation of the celestial bodies, the constellations named after the ancient astrological signs now shifted 23 astrological degrees from the point of perfect alignment known as the fiducial point, which last occurred in AD 498. The cause of this offset is from the Precession of the Equinox, also known as a Great Year, where a 25,800 year cycle marks the movement of the vernal equinox through the signs in twelve 2160 year ages, following in the order of Aries to Pisces to Aquarius (reverse of the suns movement through the signs in a year). If one is to adjust the 30 degree boundaries around the new location of the constellations as done in the sidereal system, they will find the placement of their Sun sign and all other planets and houses in the chart have changed. In some cases individuals will have some planets falling in the shared space of the Sidereal and Tropical zodiacal signs. This can have major implications for ones reading of the chart as well as personal change from integration of the new perspective. It is possible both zodiacs have relevance, the Tropical representing the stars as they would be in their ideal placement, and the sidereal representing how they relate to the present day, or perhaps the opposite. Some arguments against the 12 sign Sidereal zodiac is that the boundaries of signs are inconsistent in size, and some of them only occupy a small portion of the ecliptic. Scorpio being on the ecliptic for under 10 degrees, and Virgo taking up over 40 degrees. One proposal to remedy this is the inclusion of a thirteenth sign, Ophiuchus, and the revision of sign boundaries to be consistent with their length on the ecliptic. This is the basis for 13 sign sidereal Astrology, a modern creation adapted to the changing stellar conditions. One problem with 13 signs is the loss of the even distribution of the four elements (Fire, Air, Water, and Earth), and the three qualities (Mutable, Fixed, and Cardinal), a key feature of knowing the nature of the signs and their alchemical relationship.