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Stars and Signs   [part two]
the Constellations vs the Sidereal and the Tropical Zodiac

In this, the second part of this article, Kevin Burk explains the difference between the Tropical and Sidereal Zodiacs, taking a sidelong glance at the Age of Aquarius and some myths and misconceptions. He argues that the Greeks never used the actual constellations to measure the positions of the planets, however, because the constellations did not divide the ecliptic into equal segments, which outlined the various qualities of different parts of the year.

Although the Tropical Zodiac is used by the vast majority of Western Astrologers, it is not the only Zodiac system. The Sidereal Zodiac (Sidereal = Star) does take the precession of the equinoxes into account, and rather than beginning its cycle at the point of the Spring Equinox each year, it begins when the Sun aligns with a Fixed Star in the Constellation of Aries. The Sidereal Zodiac is also known as the Fixed Zodiac.

While astrology was developing in the West, it was also developing in the East. Hindu astrology, called Vedic astrology or Jyotish astrology has always used the Sidereal Zodiac. Jyotish astrology has an entirely different set of techniques and interpretations for the signs and planets. The fundamentals may be the same as in Western Astrology, but the similarity ends there.

In the 1930's, Cyril Fagan began to advocate using the Sidereal Zodiac in Western Astrology, rather than using the Tropical Zodiac. Although definitely in the minority, there are many astrologers who practice Western Sidereal Astrology, using basically the same interpretations for the signs and the planets, but an entirely different measurement system. Currently, the difference between the Tropical Zodiac and the Sidereal Zodiac is about 23°. What this means is that the Spring Equinox, which occurs at 0° of Aries (Tropical) actually occurs at about 7° of the Sidereal Sign of Pisces. Because no one can agree as to the exact location of the start of the Constellation of Aries, and therefore to the point where the Sidereal Zodiac would begin, the Sidereal Zodiac is calculated backwards from the Vernal Point, using one of many different ayanamsas.

Tropical Astrology and Western Sidereal Astrology have fundamentally different approaches to the symbolism and interpretation of the Signs. Tropical Astrology believes that the qualities associated with the signs are linked to the seasons, rather than to the fixed stars, and therefore the precession of the equinoxes and the growing difference between the Tropical Signs and the relative positions of their namesake constellations is of no consequence. Sidereal Astrologers (both Western and Eastern) believe that the qualities of the signs are not related to the seasons, but rather to the specific portions of the ecliptic as measured against the fixed stars.

With respect to the question of the accuracy of ancient charts and interpretations, we only need to remember what Zodiac system was used at the time, and keep things in context. The Western Astrological tradition, which includes the Greeks, the Europeans, the English (in the Middle Ages), and the Americans in more recent years is based on the Tropical Zodiac. Therefore, all charts and interpretations from these times and places would be as accurate and valid today as they were then. Furthermore, the date, time and location information can be used to calculate a "modern" version of the ancient charts with no adjustments (except for the necessary conversions to translate the more ancient dates into the modern calendar).

Any charts from the Eastern tradition, however, as well as any Western Sidereal charts (post 1930's) would require adjustments based on the precession of the equinoxes. The difference between the Tropical zodiac and the Sidereal Zodiac changes each year, and the degree of precession would have to be taken into account for the date of the chart. This would be rather nightmarish to try and calculate by hand; fortunately, most computer astrology programs that offer a Sidereal Zodiac option take this into account and can produce accurate Sidereal charts for any time or place.

Go to Top A Digression into the Age of Aquarius

The precession of the equinoxes has to do with more than just the two different zodiac systems. As the equinoxes precess, they relate to the Great Ages of Man. These Ages mark different periods where significant evolutionary changes occurred. The Ages are defined by the Sidereal Sign that is the current location of the Vernal Point. Currently, the Spring Equinox (0° of Aries in the Tropical Zodiac) occurs at about 7° of the Sidereal Sign of Pisces, and we are currently very much in the Age of Pisces, where we will stay for another 150-300 years or so until the Spring Equinox precesses into the Sidereal Sign of Aquarius, which will mark the beginning of the Age of Aquarius. (Even agreeing on this definition of the "Ages" there is much dispute as to the actual year that the "Age of Aquarius" will begin. The reasons and reasoning for this aren't terribly important to this discussion. Suffice it to say that it's not terribly likely that any of us will still be here to witness it.)

Each Great Age is associated with a major evolutionary and cultural advancement of the species.

  • In the Age of Gemini, language was developed.
  • In the Age of Taurus, agriculture was discovered, and for the first time, towns, villages, and cities were formed because humans no longer needed to hunt and gather for their food and so were not required to be so nomadic.
  • The Age of Aries ushered in wars and warfare, violence and conquest.
  • The Age of Pisces has been dominated largely by religion, Christianity in particular, with its peculiar mixture of persecution and spiritual salvation.

The general thoughts about the Age of Aquarius are that it will mark a period of enlightenment and freedom. But once again, even the most generous estimates put this off for another 100 years at least.

Go to Top Myths, Misconceptions and Misinformation

The fact that the Signs of the Zodiac share the same names as 12 of the constellations, and were, in fact, named after the constellations, has resulted in the popular misconception that the signs are the same thing as the constellations. This fallacy has given rise to all sorts of pseudo-scientific attacks on the validity of astrology, all of which come from individuals who do not understand astrology in the first place. Some have even come from a small faction of Western Sidereal astrologers who attempt to discredit Tropical astrology. I'll list some of the most popular examples below, and then, since they all can be explained or refuted by the same information, tackle them all at once.

  • "The 13th Sign of the Zodiac." This one pops up in the media from time to time. Sometimes it takes the angle that a new sign of the zodiac has been "discovered." Other times, it's used as an argument by sceptics attempting to discredit astrology. What it refers to is the Constellation of Ophiuchus, which also intersects the ecliptic, and which actually occupies more space along the ecliptic than the Constellation of Scorpio.

  • "The Sidereal Zodiac is the only 'real' zodiac because it uses the constellations and not imaginary divisions of the ecliptic."

  • "How can you say that 'Jupiter is in Libra' when I can look up in the sky and see it clearly in Virgo?"

  • "The Zodiac has all of the dates wrong because of the Precession of the Equinoxes." Part of this is addressed above when the difference between the Tropical and the Sidereal Zodiacs is covered. The rest will be addressed below.

The data in the following table was published by Dr. Lee T. Shapiro, Director Morehead Planetarium, CB #3480 Morehead Building, University of North Carolina, Chapel Hill, NC 27599-3480. The dates and days refer to the time that the Sun appears to spend in each of the constellations. I took the days (based on a 365 day year) and converted them to the corresponding arcs that each constellation occupies along the ecliptic. I also included the approximate dates that the Sun enters each of the Signs, both in the Tropical Zodiac and also in the Sidereal Zodiac.


Sun Enters/Leaves

# of Days

# of Degrees

Tropical Dates

Sidereal Dates


Apr 19–May 13



Mar 21–Apr 20

Apr 14–May 14


May 14–Jun 19



Apr 21–May 21

May 15–Jun 14


Jun 20–Jul 20



May 22–Jun 21

Jun 15–Jul 15


Jul 21–Aug 9



Jun 22–Jul 22

Jul 16–Aug 16


Aug 10–Sep 15



Jul 23–Aug 22

Aug 17–Sep 16


Sep 16–Oct 30



Aug 23–Sep 23

Sep 17–Oct 16


Oct 31–Nov 22



Sep 24–Oct 23

Oct 17–Nov 15


Nov 23–Nov 29



Oct 24–Nov 22

Nov 16–Dec 15


Nov 30–Dec 17






Dec 18–Jan 18



Nov 23–Dec 21

Dec 16–Jan 13


Jan 19–Feb 15



Dec 22–Jan 20

Jan 14–Feb 12


Feb 16–Mar 11



Jan 21–Feb 19

Feb 13–Mar 12


Mar 12–Apr 18



Feb 20–Mar 20

Mar 13–Apr 13

The table should illustrate clearly the difference between the signs and the constellations. The signs, you will remember, are units of measurement, each consisting of 30 degrees of arc. The constellations may take up an average of about 30 degrees of arc each, but they certainly aren't very useful as units of measurement.

This is also the answer to the "13th Sign" myth. While there are most certainly 13 constellations that cross the ecliptic, the signs are not the same thing as the constellations. Why the Ancients chose to name the 8th Sign after Scorpio (which barely takes up 7° of arc) rather than Ophiuchus (which covers a more respectable 17.75°) will probably remain a mystery.

It should also be obvious from looking at this table that the Sidereal Zodiac does not rely on the constellations any more than the Tropical Zodiac does. While there is certainly a greater correlation between the Sidereal Signs and the constellations along the ecliptic, again, the constellations do not divide the ecliptic into equal segments and therefore they are not used as the basis for the Sidereal Zodiac. In fact, there even appears to be a discrepancy between when Dr. Shapiro notes that the Sun enters the Constellation of Aries and when the Sidereal Sign of Aries is thought to begin (for the year 1997).

The discrepancy between where astrologers place a planet in the night sky, and where astronomers place that same planet is also related to the difference between the Constellations, the Tropical Zodiac and the Sidereal Zodiac. Based on the dates in the table, on October 24, the Sun would be found in the Constellation of Virgo, the Tropical Sign of Scorpio, and the Sidereal Sign of Libra.

And finally, the argument that astrology can't work because the precession of the equinoxes make it invalid, or at least wildly inaccurate (which is essentially what the "scientist" was referring to who prompted Debbie's question), simply brings up the difference between the Tropical and the Sidereal Zodiacs. Along the ecliptic, again, the constellations do not divide the ecliptic into equal segments and therefore they are not used as the basis for the Sidereal Zodiac. In fact, there even appears to be a discrepancy between when Dr. Shapiro notes that the Sun Enters the Constellation of Aries and when the Sidereal Sign of Aries is thought to begin (for the year 1997).

Once again, although the Tropical and the Sidereal Zodiacs are very different, they each represent an entirely valid system of astrology.

This concludes the article by Kevin Burk.

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Stars and Signs: part 1 | part 2 | Hellenistic Astrology | An Amazing Encounter | Nexus of Probability

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This page was last modified on Saturday, 4 June 2016