An explanation of some technical terms
The Zodiac
The apparent path of the Sun around the Earth (we all know the
Earth really goes round the Sun) is called the Ecliptic - because
eclipses take place along this line - and the planets (with the
exception of Pluto) are usually found within plus or minus 8°
of it. This band around the ecliptic is called the Zodiac.
So far so simple, but there are many zodiacs, how do we know where
each starts? Now we come to the ancient question "How long
is a piece of string?", or alternatively, "Where is the
beginning of a circle?" Where do we put the start point?
Western Astrology uses the Tropical Zodiac which is defined by
the interaction of the movement of the Sun and Earth. There are
no stars or constellation involved in this zodiac. It starts at
the vernal point, that is the crossing point of the Celestial Equator
and the Ecliptic when the Sun is travelling north. The Celestial
Equator is the Earth's equator projected into space. The Sun on
its journey "around the ecliptic" reaches these crossing
points at the spring and autumn equinoxes. The spring equinox is
also the first point of Aries and it is this point which is chosen
to be the starting point of the Tropical Zodiac. The signs are divisions
of 30 degrees from this point.
The Sidereal Zodiac bases itself upon the stars. The exact start
point is an area of discussion and so there are several calculations
which mark the start of the sidereal zodiac. The signs are divisions
of 30 degrees from the selected point even though the actual constellations
are not all the same length.
The other common zodiac is the Draconic Zodiac which uses the North
Node of the Moon as its starting point. Again the signs are divisions
of 30 degrees from this point.
These three zodiacs are very rarely in line with each other. When
they do line up, some would say they herald significant times. The
last time the sidereal and tropical zodiacs lined up was around
the time of the birth of Christ.
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