This is due to the phenomenon known as "the precession of
the equinoxes." The equinoxes are the points in time and space at
which the earth, with its tilted axis, is positioned with respect
to the sun in such a way that the length of day and night are
equal. Most Western astrologers, with a few exceptions, base
their work on a zodiac with sign positions determined by the
equinoxes rather than the constellations. At the Vernal Equinox,
which occurs on about March 20th of each year, the Sun enters
into the sign of Aries in this zodiac. The signs are not defined
by the constellations. The zodiac positioned with respect to the
equinoxes is called the "tropical zodiac." (A zodiac based
loosely on the constellations [with the first sign beginning at
the edge of the constellation Aries, and with 12 equal signs of
30 degrees each], which is called the "sidereal zodiac," is used
primarily by Hindu astrologers.) Because of the precession of the
equinoxes, the equinoxes are moving backwards with respect to the
fixed constellations by about one degree every 72 years.
Approximately two thousand years ago, the beginning of the
tropical sign of Aries was aligned with the beginning of the
constellation Aries (perhaps around 217 A.D.).
<p>
Why do the tropical signs have the same names and symbols as the
constellations with which they were aligned 2000 years ago? Isn't
the sidereal zodiac the source of the meanings of the tropical
signs? And so shouldn't astrologers take the meaning of a
tropical sign from the constellation most closely aligned with it
now? This argument is based on the presupposition that the
meanings of the signs come from the natures of the symbols in the
heavens that we call constellations. But clearly this is not the
case. Some of the most dominant traits of Virgo are obsession
with detail and an analytical and critical nature. How could
these traits be derived from a picture of a virgin? How could the
Piscean qualities "spiritual," "selfless," "imaginative,"
"inspirational," "feminine," and "idealistic" be derived from a
picture of two fish? Few traits of each sign can easily be
related to the symbol assigned to the constellation of the same
name.
<p>
There is no necessity, given current knowledge, for the tropical
signs to have received their meaning from the constellations of
the sidereal zodiac; it is possible that the nature of the
tropical signs suggested a symbol to associate with a
constellation (since the symbols look very little like the
pattern of stars we associate with them). Perhaps the
constellations with which we are familiar came into being during
the period in which the tropical sign Aries was aligned with the
constellation Aries. When did the tropical zodiac and
constellations appear? The tropical zodiac may have been around a
long time. The Egyptians had a tropical (solar) calendar by the
early part of the third millennium B.C.; given the direct and
transparent relationship between the signs of the tropical zodiac
and the months of the solar year, they may well have had a
tropical zodiac as well. Tropical calendars in the form of
standing stones (e.g., Stonehenge) date from 1000-5000 B.C. in
Northwest Europe, so the tropical zodiac might have existed there
as well. Unfortunately, the preliterate people of these cultures
left no records behind. Some sort of zodiac, possibly sidereal,
with 12 equal signs, existed in India in 3000 B.C. A manuscript
(in Sanskrit) from that period shows that astrologers then used a
zodiac, an equal house system, and aspects counted sign to sign
(as in much modern-day Hindu astrology).
<p>
The origin of the modern constellations is somewhat obscure, so
it is very difficult to decide whether the constellations were
around to lend meaning to the tropical signs at the time that the
tropical zodiac was created. Noonan (1976; Journal of Geocosmic
Research, Vol. 2, No. 1, pp. 6-7) claims that the first zodiac of
the constellations appeared around 500 B.C. The constellations
are believed to have been assigned symbols by the Babylonians,
but there were originally 36 constellations, and only some of
them coincide with the modern sidereal signs. We know that some
of the symbols used for the modern signs are recent, because the
original symbols were all animals (the word "zodiac," derived
from the Greek zo^idiako's, means "circle of animals"). We can be
certain that the modern constellations of the zodiac existed by
about 30 B.C. because they appear very clearly on the ceiling of
the Temple of Hathor at Dendera in Upper Egypt. So was the
tropical zodiac in use by then?
<p>
It might have been. The precession of the equinoxes was certainly
common knowledge by then. Precession was discovered at the very
latest in 200 B.C., when Hipparchus wrote about it. But Sir
Norman Lockyer found that many very early temples in Egypt had
been moved at different periods in history so that they lined up
with a particular star as it precessed across the sky.
<p>
(See, for example, E.C. Krupp, "In Search of Ancient
Astronomies," New York: Doubleday, 1977.)
<p>