Back to basics
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The star groups forming the images of the Star Signs are not all equal in size. Some constellations are larger than others. For example, the group of stars that make up Aries is significantly smaller than the collection of stars named Pisces. That is why in the course of the year we don’t see the Sun pass through twelve Star Signs of exactly 30 degrees each, but through a series of constellations of varying sizes.
In addition, due to internal movements within these star constellations, their sizes are constantly changing. Over the course of the centuries, some groups are getting smaller while others are expanding.
These internal movements also imply that the border stars of the Star Signs are changing position. This leaves the demarcation between adjacent Star Signs more and more open for discussion.
So as the years are passing by, more and more uncertainties arise, especially regarding the placement of planets within the Signs of the Zodiac.
As far as we know, prior to the times of the ancient Greeks no complete horoscopes were set up. Whenever a star or star constellation was seen rising at the horizon, the Babylonians and Egyptians considered this as an omen, either good or bad. Any omen was taken to refer to a general, collective trend. The daily changes in planetary positions were not given much thought and were not taken into account. In the era of omen astrology, a precise method for locating the planets within the Zodiac was therefore not developed.
The ancient Greeks, however, showed an increasing interest in the individual. People started to become interested in the relationship between their individual existence, restricted in time and space, and the cosmic constellations surrounding them. Unlike omen astrology, Greek astrology did attach value to the daily dance of the planets. In order to be able to register planetary positions in a reliable way, they needed a verifiable frame of reference. Unfortunately, the Zodiac didn’t offer the required consistency for this, as explained above.
In order to provide a more reliable frame of reference, Euktemon (5th century BC) decided to divide the Sun’s orbit around the Earth into twelve equal segments. This artificial division he called the Ecliptic, also known as the tropical Zodiac. The names and core qualities of each of those twelve segments he derived from the Star Signs of the actual, sidereal Zodiac. He connected both imaginary belts by aligning the Spring or Vernal Equinox of the sidereal Zodiac (the moment in spring when day and night are of equal length) with the Sun’s position at the First Point of Aries on the Ecliptic.
From 431 BC onwards, he used this division for all his measurements. Later, in the 2nd century AD, Euktemon’s division was conclusively confirmed by the influential Greek astronomer and mathematician Ptolemaeus. Ever since Ptolemaeus, the tropical Zodiac has been used as a general frame of reference.
However, towards the end of his own life, Euktemon already noticed that at the beginning of spring, when day and night are equally long and the Sun passes the Spring Equinoctial Point in the Ecliptic, this point was no longer visible against the background of the First Point of Aries in the Sidereal Zodiac. It turned out that there was now a slight difference between the First Point of Aries in the tropical Zodiac as defined by Euktemon and the First Point of Aries in the sidereal Zodiac behind it. Later it was found that this deviation was caused by a slight time difference in the Sun’s journey along both orbits. The result is that the distance between the two First Points of Aries is steadily increasing over the years.
The Spring Equinox
The difference in the Sun’s orbiting time when passing through both zodiacal belts, amounting to approximately 20 minutes a year, results in a slow but steady regression of the tropical Spring Equinox compared to the Spring Equinox in the actual, Sidereal Zodiac. Now, more than twenty centuries later, our tropical Spring or Vernal Equinox has regressed through one whole Star Sign of the sidereal Zodiac. It is now located at the beginning of the Sign of Pisces, or possibly already at the end of Aquarius. We don’t know this for sure, because as explained earlier, in the Sidereal Zodiac the boundaries between the Star Signs have become uncertain. One thing is clear, however: the Star Sign positions in these two Zodiacs have grown quite far apart.
Another thing that is clear is that Euktemon’s division of the Sun’s orbit around the Earth has led to a measuring instrument that is not related to its underlying frame of reference in the way he had intended.
Nevertheless, Western astrology has always kept working with his division, without any reservations, for the simple reason that it produced results. Which is remarkable in itself!