ure lession).
Soooo, "what's the difference between these two zodiac systems?" you ask... Well, there's only one difference really, and that is where they begin. The Tropical Zodiac begins in the "sign" of Aries on March the 21st whilst the Sidereal systems currently start with the zodia of Aries about a month later (the actual dates can be found in form here, at a nifty sidereal astrology site). This one point makes for a HUGE difference - according to the Tropical zodiac system you may be a Sun-Sign of Sagittarius and under the Sidereal zodiac system, an Ophiuchus*! This is the effect that a simple disagreement over the zero point of Aries can cause.
Here is a graphic that illustrates the difference between the zodiac systems: Thanks to "Vedic Astrology Helpline" @ http://www.osfa.org.uk/pictures.htm (This graphic is not meant to be offensive to farmers, ranchers, or others who might use the term "cowboy" or "vaquero" to describe themself... I just liked this because I imagined the illustration being of me telling Prez Bush about sideral astrology.)
So now you are probably wondering how there can be TWO places in the sky called "Aries"... Well, the Sidereal zodiac system's Aries corresponds to where Aries is in the sky overhead. If you use a sky map or astronomical ephemeris, there will be agreement between where the planets are in the chart and where they are on an Sideral astrology chart. There is no disagreement between astrology, astronomy, and the stars overhead when using a sidereal zodiac system.
The Tropical zodiac system's sign of Aries corresponds to where Pisces is in the sky - and to where Pisces is in the Sidereal zodiac system. This is important, because (for example) the Sun is seen to be in the constellation Pisces when the Vernal Equinox occurs around March 21st each year. This is why Classical Astrologers and other people say that this is the Age of Pisces. The Sun is in Pisces at the beginning of Spring - which was the beginning of the year on some ancient calendars. The Tropical zodiac system can be seen to be from the Age of Aries since it expects the Sun to be in that constellation at the beginning of Spring... and this shows us that astrology is very, very, VERY old.
So... now that you see the difference between the two types of Zodiacal Systems, let's talk about another difference between Classical and Modern Astrology - the "zodia" or "signs" of astrology.
The next most important concept to understand when studying or using Hellenic Astrology is that of the zodia. Zodia are what are called "signs" in modern Astrological systems - the 30 degree divisions of the Tropical Zodiac which are named Aries, Taurus, Gemini, etc. I will give their full characteristics in another post, but for now it's enough to just know that "zodia" are the same as "signs".
Hellenic Astrology uses house=sign chart design. This is different from many of the house systems used in most modern Astrology. In Hellenic Astrology, the houses are called topoi or topos in the singular; this is Greek for "place" and has the same connotation as "house" does in modern Astrology... for example, the second topos is the topos of land, material goods, and talents. Because each topos = a single zodia, it becomes very easy to see the relationships between planets based upon the relationships between their polarity, modalities, and elements. It is the interactions between these qualities of the planets that provide the key to understanding and interpreting an aspect pattern within a chart (either personal or mundane).
The major difference between aspects as used in Hellenic Astrology and aspects used in Modern Astrology is that aspects are determined according to topoi and zodia as opposed to individual planets. For example, all planets within a single zodia and topoi are considered to be aspected to all of the planets in another zodia and topoi. The aspects that are discussed within Hellenic Astrology are often referred to as the "Platonic Aspects" as they were first outlined and described in Ptolemy's work Tetrabiblos.
The Ptolemaic aspec