Sidereal Astrology

The Tropical and Sidereal Zodiaks
& The Cycle of Earth's Precessional Cross

by Nick Anthony Fiorenza


This article explores Earth's ~25,000-year precessional cycle; the ever changing relationship between the tropical and sidereal zodiacs; the astrological ages, the intercession of the Earth's Precessional Cross; measurement of the precessional rate, and the "Galactic Equatorial Ayanamsa"—reckoning of the sidereal zodiak based on the spherical geometry of Earth's precessional Cross.

Precessional Cross Movies
Earth's Precessional Cycle and the Creation
of Earth's Precessional Cross

Earth's Precession

Earth's polar axis precesses very slowly over a period of about 23,000 to 26,000 years. The term precession simply refers to a change in the direction of the axis of a rotating object. As this occurs, the pole of the Earth inscribes an arc in the heavens called the precessional arc. Earth's pole aligns with different pole stars throughout its precessional period. Polaris is Earth's current north-pole star. Earth's ~25,000-year precessional cycle is also referred to as "Earth's Great Year."

Precession of the Equinoxes

Earth's Precession

Because Earth's axis is tilted 23° 27' with respect the plane created by Earth's orbit around the Sun (the ecliptic plane), Earth's equatorial plane (green) is also tilted at this same angle with respect to the ecliptic plane (blue). These two intersecting planes (Earth's equatorial plane and the ecliptic plane) create an intersecting line in the ecliptic called the vernal axis. Looking from Earth, we see one point along this axis lying in one direction in the ecliptic, and the other lying in the opposite direction. One point is the location in the ecliptic where we see the sun on the March equinox. This location is the vernal point (VP). The other point is the location where the sun resides on the September equinox. This is the anti-vernal point.

As Earth's pole precesses, so to does Earth's equatorial plane and subsequently the vernal axis (moving in a counter-clockwise motion). Thus, the vernal axis (the vernal equinox points) move around the ecliptic at a rate of precession, which is currently measured to be about 1° in 72 years, making one complete cycle in about 23,000-26,000 years. The precessional movement of the vernal points is called the "Precession of the Equinoxes."

The Cause of Precession

Although this article is not about the "cause" of Earth's precession, it is appropriate to mention that Earth's precession is not fully understood and there is more than one hypothesis as to its cause. The simplest reason for Earth's precession, although an assumption, is the reason that is most commonly known. This model explains that the Earth's pole wobbles over a very long period of time, much like a rapidly spinning top's axis wobbles at a much slow rate than its spin. Another model is the "Binary Star Model" hypothesized by astrophysics researcher Walter Cruttenden; et. al. Although the reason for our Sun to move in a curved path may not be fully understood, and there may be unknown causes for it, he and his team hypothesize that the solar path's curvature is caused by a binary star model, where our sun and another sun orbit each other. Astronomer Glen W. Deen proposes a Ternary Star System (our sun with two other suns). Independent of the cause, the precession of Earth's pole and that of the vernal axis with respect to the stars still occurs.


Walter Cruttenden's binary star hypothesis:

Glen W. Deen's ternary star system hypothesis: "The Time of Perihelion Passage and the Longitude of the Perihelion of Nemesis" Full article PDF

This article is not intended to favor or debate the cause of Earth's precession; it is about the precessional cycle itself; the relationship between the tropical and sidereal zodiaks; and the role of Earth's precession cycle in the evolution of human consciousness.

Precession of the Tropical Zodiak & the Astrological Ages

The vernal point is also the fiducial (reference point) for the tropical zodiak, defining 0° tropical Aries. Because the vernal point moves in the ecliptic, the entire set of signs comprising the tropical zodiak also moves with respect to the stars (and the sidereal zodiak), which remain fixed in their location in the heavens.

Sidereal-Tropical Drift

The location of the vernal point in the sidereal zodiak defines the current zodiakal age. The sidereal zodiak is a set of signs, much like the tropical signs, except they do not move in the ecliptic. The sidereal signs are aligned with their corresponding constellations. The tropical zodiak aligned with the fixed sidereal zodiak around 200 CE. but has since drifted 25°; i.e. this was when zero degrees tropical Aries aligned with 0° sidereal Aries. The vernal point currently resides at about 5° sidereal Pisces as it slowly moves toward the sidereal sign of Aquarius—thus we are completing the age of Pisces. We will formally enter the age of Aquarius when the vernal point precesses to 0° Aquarius—in about 360 years (5° x 72 yrs) from now (2000 C.E.). The vernal point is also called the Birthplace, or the Office of the Christos (point of the sun/son/soul)—governing the timing of the re-birth of soul consciousness into the world.

The vernal point's arrival to 5° sidereal Pisces at this time in Earth's precessional cycle (circa 2000 CE.) creates a primary event that supersedes the importance of changing zodiakal ages: this event is the formation of a perfect cross in the cycle of Earth's Precession of the equinoxes. The formation of this precessional cross is explained below.


The center (blue) ring in the above illustration is the sidereal zodiak. The signs of the sidereal zodiak align with their corresponding constellations and their stars. The sidereal zodiak does not move. It is referenced to the fixed stars in the heavens, or to the fixed and primary galactic equatorial axis in the ecliptic (the horizontal line). This axis is created by the intersection of the ecliptic plane and the galactic plane, which are tilted with respect to each other by 60°. The two nodes of this axis in the ecliptic are the “Galactic Equatorial Node” (GEN) at 5° sidereal Sagittarius, and the anti-GEN at 5° sidereal Gemini. They are also called the “Gate of God” and the “Gate of Man.”

The outer (violet) ring reveals the thirteen ecliptical constellations (not signs). This ring shows where the boundaries of the actual constellations cross the ecliptic. The constellation Virgo encompasses the largest length of the ecliptic (about 44°). The constellation Scorpio dips south of the ecliptic plane with only the Scorpion’s head lying upon the ecliptic—encompassing only about 6° of the ecliptic. Ophiuchus, the serpent holder, stands upon the Scorpion and crosses the ecliptic—thus creating the thirteenth ecliptical constellation (not sign).

The inner (green ring) is the tropical zodiak (at 2000 CE.) The tropical zodiak moves around the ecliptic with respect to the fixed stars—with respect to the sidereal zodiak and to the constellations. It moves because 0° tropical Aries is referenced to the moving Vernal Point. The Vernal Point moves around the ecliptic at a rate of about 1° every 72 years (once around the ecliptic in Earth's ~25,000-year precessional cycle) due to Earth's precession. The tropical zodiak and its signs are not reference to the stars or actual constellations, the tropical signs are referenced to Earth's seasons (the Vernal Point is where the Sun resides in the ecliptic on the spring equinox, as experienced in the northern hemisphere). The signs of the tropical zodiak are currently miss-aligned with the true sidereal signs (and the energies of the actual stars and constellations) by ~25°, and they are drifting further and further apart due to Earth's precession.

Aldebaran, Eye of the Bull, and Antares, Heart of the Scorpion, mark the center of their respective sidereal signs: 15° sidereal Taurus and 15° sidereal Scorpio. The Babylonians referenced the sidereal zodiak by these stars. Aldebaran, Antares, Regulus (Heart of the Lion), and Fomalhaut are called the Four Royal Architects, giving structure and order to the Heavens. Regulus is Chief or King of the Four Royals. It is the only one of the four lying exactly on the ecliptic plane. Residing at 5° sidereal Leo, Regulus is also the only one aspecting the Galactic Equatorial axis. Regulus, or “the Rex” means the Law Giver—a clue to its astrological influence as the Heart of the Lion.

The Galactic Axis of Earth's Precessional Cross

Just as Earth is tilted with repspect to its orbit around the sun, so too is our solar system tilled with repspect to the the plane of our galaxy. The ecliptic plane is tilted about 60° to our galaxy's equatorial plane. This creates another intersecting line, one which remains stationary (relative to Earth's precessional period). This axis is called the galactic equatorial axis and it is the fixed axis of Earth's Precessional Cross. The primary reference point of this axis is the galactic equatorial node (GEN), which resides at 5° sidereal Sagittarius. This node is called the "Gate of God." Its opposite point, the anti-GEN, resides at 5° sidereal Gemini and it is called the "Gate of Man."

Celestial Plane - Ecliptic Plane
Ecliptic Plane - Galactic Plane
Celstial Plane - Ecliptic Plane - Galactic Plane

Earth's Precessional Cross

The changing relationship between these two axes ( the moving vernal axis and the fixed galactic axis) creates the "Cycle of Earth's Precessional Cross." As the vernal point (VP) moves around the ecliptic, it changes its geometric relationship to the fixed galactic equatorial node (GEN). The vernal point currently resides at the 3/4 point (270°) in its cycle, making the vernal axis exactly perpendicular to the galactic axis, thus creating a perfect cross in the ecliptic—the Erect Precessional Cross. This exact precessional cross occurred in July of 1998. I generally round this date to 2000 CE. to simplify discussion. See Timing of Earth's Precessional Cross for more details.

Earth's Precessional Cross over time

Intercession of Earth's Precessional Cross

I suggest the Cycle of Earth's Precessional Cross is the timepiece that drives the "Evolutionary Cycle of the Soul" collective on Earth—revealing the unfoldment of human consciousness. We are just emerging from the last 12,000 years of temporal darkness, which began at the last (90°) erect cross (about 10,000 to 12,000 years ago), the time of separation from unified awareness—the time of the "Biblical Flood." The erect precessional cross occurring now (~2,000 CE.) marks the time in our Great World Cycle where a re-unification in consciousness begins.

The erect cross occurring now creates a primary transition in the Cycle of Earth's Precessional Cross, in the "Evolutionary Cycle of the Soul." This event is far more significant than the changing of an astrological age; i.e., the four primary divisions of a circle referenced to the galactic equatorial axis supercede the 12-fold division of tropical zodiak reference to the 12-fold divisions of the sidereal zodiak.

See the "Earth's Precessional Cross" section of this web site to learn more about the Cycle Earth's Precessional Cross and the evolution of human consciousness.

The Sidereal and Tropical Relationship

Just as the tropical signs are referenced to the moving axis of Earth's Precessional Cross, the fixed sidereal signs are referenced to the fixed, galactic axis of Earth's Precessional Cross. Because of the precession of the equinoxes, the tropical signs continue to drift from the sidereal signs and further from the true star positions that characterize the signs to start with. Although the twelve divisions of both zodiakal systems are created by natural harmonics occurring in the ecliptic, they are harmonics referenced to different realms of consciousness. The RELATIONSHIP of the moving tropical zodiak with respect to the fixed sidereal zodiak reveals the nature of the relationship of incarnate personality consciousness with respect to the true soul level awareness—that is, where we are in the evolutionary unfoldment of human consciousness, in the Evolutionary Cycle of the Soul.

Why Two Zodiaks

First, we must realize that the wisdom of the true astrology of the ancients, as with other esoteric (Gnostic) wisdom, was transferred (taken) from Babylon, Caldia, and Egypt, and then it was eventually bastardized into a confused menagerie. This seems to have started with the dominating influence of Alexander the Great, king of Macedonia (336 to 323 BCE), who catalyzed an amalgamation of Egyptian, Babylonian, and Greco-Roman thought into a new cultural expression in the 4th century BCE; and later by Ptolemy.

Subduing Egypt during his conquerings and explorations, Alexander proclaimed himself Pharaoh in 332 BCE while placating native priests at Memphis. He founded Alexandria, which was to become a primary intellectual center, and which was primarily Greek and Jewish. Here, miss-understood Egyptian mysteries and Greek philosophies merged into the "Mysteries of Serapis." This was the cultural emergence of esoteric teachings prominent throughout Alexandria's golden age. (Mysteries simply means esoteric teachings about life, not unfathomable or secret.) Also a center for Jewish learning, the Great Temple of Serapis is believed to be where the Old Testament was translated from Hebrew into Greek. Alexander's dominating influence in coastal Egypt and his further conquest of Babylon along with much of Asia Minor laid the foundations for the various religious factions of the Greco-Roman world. (Alexander attempted to create a master race through a genetic fusion of Macedonian men with Persian women—just one example of this megalomaniac's brutal conquests.)

Beginning with the death of Alexander in 323 BCE and continuing through around 31 BCE, the Hellenistic Period gave birth to a diversity of esoteric philosophies and occult practices, all derived from the Egyptian and Babylonian mysteries. The cultural peak of this period, from 280 BCE to 160 BCE, produced Euclid, Hipparchus, Eratosthenes, Dionysius and many other creative thinkers, who all expounded upon the cultural influence of Ancient Egypt. However, although this period carried forth some of the ancient esoteric teachings in a new intellectual language, it also produced a highly intellectualized amalgamate of confused ideas. The Hellenists bastardized Egypt's already cryptic and esoteric language into near total confusion because the majority of the Hellenistic culture did not have the perceptual awareness to comprehend matters of the soul, nor had they the capacity to intellectually comprehend Egypt's mythical picture language. Instead of grasping the language (astronomical mythical images as well as Egyptian hieroglyphics) from a soul perspective and realizing the transcendent wisdom of the evolutionary journey of the soul, the Greco-Romans attempted to translate this picture language from the perspective of the limited personality. This reduced Ancient Egypt's esoteric wisdom into a non-sensible confusion of men worshipping a pantheon of gods and stars. The dispersion of this confusion from Alexandria into Eastern Europe through the centuries ahead led to confused occult practices and perverted systems of belief that ran rampant throughout Eastern Europe at the time. The Roman Empire, Christianity and Byzantium, and their various sects—all derivations of the esoteric wisdom of Ancient Egypt—were the eventual result of this confused cultural fusion that originated in and migrated from Alexandria.

Prior to the early few centuries of the first millennia, planetary measurement was always referenced to the fixed stars (sidereal) as was the astrology of the ancients (Babylonia, etc). Astronomy and astrology were always one and the same until the Greco-Roman church-state astronomers began to record planetary ephemerides referenced to the moving vernal point rather than to the fixed stars, but ignoring that the vernal point moved with precession, and while maintaining that all other heavenly bodies rotated around the Earth—a statement certainly affirming true egoic consciousness. (This was due in particular to Claudius Ptolemaeus (c. 90 - c. 168 CE) who was employed by the Greco-Roman controlling faction. Ptolemaeus was a mathematician, not a true astronomer. Some assert he never even looked into the heavens as an astronomer would look (Allen).) To say anything other than Earth was the center was heresy, so only those willing to sell out to the manipulative ploys of the church-state, and perpetuate the asserted geocentric dogma of western Christendom, stayed on the pay-role and kept their heads (actually, heretics were burned at the stake!). Here was planted the bastardization of true soul level astronomical astrology, and here began the Hellenistic, Ptolemaic, tropical astrology during an age of suppression, and which is still in vogue today. This is not to say either way that Ptolemy was ill-intended or was deliberately trying to mislead—a topic of controversy amongst historians. However, it was merely the nature of the times and the natural course of evolution, a time of trying to re-emerge from the lost wisdom of the ancients amalgamated with manipulative powers attempting to control empires, land and people. People from the future may say the same for us now.

This manipulation and bastardization of the true astrological artscience into tropical astrology also affirmed that people had a finite life at the end of which they would either be saved or punished depending if they followed the dictums of the controlling political-religious factions, thus squelching any desire for individuals to spiritually aspire and awaken to the greater truth that they were durative, continually evolving souls; parts of, not separate from a greater unified intelligence. The true and greater art-sciences including astronomical astrology, Pythagorean sacred geometry, harmonic math, and other such art-sciences, were forced underground until the later time of Nicolaus Copernicus in the 1500’s who finally triumphed in eradicating the perpetuated dogma that Earth was the center around which all other heavenly bodies rotated—the egoic head-trip of the Greco-Roman church-state. From here, others would follow: Tycho Brahe (1546-1601), Johann Bayer, and later yet, Johann Kepler (December 27, 1571 - November 15, 1630), who, in the early 1600’s, brought forth the truth of the occulted astronomical and mathematical wisdom based in harmonic resonance that had been long lost. Kepler's most famous book is "Harmonia Mundi" (Harmony of the Worlds). Kepler was a mathematician, astronomer AND astrologer (responsible for revealing the affect of many astrological aspects / harmonics). Kepler is sometimes referred to as "the first theoretical astrophysicist."

It is interesting to note that many of the religions of the world, as well as the perpetuation of "tropical astrology" are based on the confused mentalities common to the early first millennia. It is also interesting to consider that the perpetual use of tropical astrology today is an energetic that perpetuates a chasm in time that continues to widen at the rate of Earth's precession, one keeping the masses drifting in time-confusion rather than living in the present and truth that the true sidereal zodiak reveals.

It is now common practice in academic and scientific publications and by secular publishers to use the neutral terms BCE (Before Common Era) and CE (Common Era) to replace B.C. (before Christ) and A.D. (after the death).

Houses of the Sun - The Tropical Zodiak

As revealed in the recent and comprehensive work, "History of the Zodiac," an in-depth exploration of the origins of the Babylonian Zodiac and its location in the ecliptic, originally a Ph.D. thesis, by Dr. Robert Powell (Sophia Academic Press, San Rafael, California 2007), the division of the ecliptic into tropical astrological signs was originally a derivation of Euctemon's tropical Calendar of Seasons (432 B.C.); "...dividing the solar year into twelve equal months commencing with the vernal equinox, in which each solar (tropical) month is named after one the twelve signs..." (Powell). The tropical calendrical system (referenced from the vernal point) was merely used as an astronomical coordinate system for measuring time in the solar year, at or just after the time of Hipparchus. Astrological qualities were later attributed to the twelve calendar months (tropical signs) through the influence of Ptolemy, and the true (sidereal) zodiak, thus faded into obscurity. Unfortunately the term "signs" had replaced "months." The tropical calendar (tropical zodiac) was based upon the sun's declination above and below the earth's equator, not upon the sun's true ecliptical location amongst the stars. From an astrological perspective, I suggest the tropical signs should be called "Houses of the Sun," more aptly describing their true historical origin, as eloquently revealed in Robert Powell's work "History of the Zodiac"—recomended reading for all astrologers and astronomers.

The Galactic Equatorial Ayanamsa: Reckoning of the Sidereal Zodiak

Calculating the exact location of the sidereal cusps in the ecliptic is a topic of debate amongst scholars due to star and planetary placements being measured from the moving vernal point. The exact distance in arc degrees between 0° tropical Aries (the vernal point) and 0° sidereal Aries must therefor be calculated. This distance is called the "ayanamsa" (the Hindi spelling of the Sanskrit ayanâmsha, which means ”part of a path”). There are many ayanamsas (or ayanâmshas) in vogue today, all varying slightly from one another. Most ayanamsas are reckoned to the stars. This poses a problem because today we recognize that stars are not really "fixed,: but do actually move and in many different directions. A stars movement is called its "Proper Motion." See "The Proper Motion of the Stars of Ursa Major" for an example.

One of the most common ayanamsas is the Fagan-Bradley Ayanamsa. It is reckoned to the star Spica in sidereal Virgo. The Fagan-Bradley Ayanamsa is 24° 44' 12" @ 2000 CE. This means that on Jan 1, 2000, 00:00:00: GMT, the tropical zodiak has drifted backward from the fixed sidereal zodiak by 24° 44' 12" based upon the Fagan-Bradley Ayanamsa. This places the vernal point (0° tropical Aries) at 5° 15' 48" in sidereal Pisces. Other arguments adjust the sidereal signs such that Aldebaran's ecliptical longitude is exactly in the center of sidereal Taurus; or that of Antares in the center of sidereal Scorpio (those being two of the four royal architects (meaning: revealing structure in the heavens). the Babylonian Zodiac is reference to Aldebaran at 15° 00'.

The recent work of Robert Powell (2007) presents historical evidence that the Babylonian Zodiac was referenced to the Aldebaran / Antares axis.

Because Aldebaran and Antares are both south of the ecliptic, it is thought by some people that it makes more sense to use a star on the ecliptic plane (0° ecliptical latitude), such as Spica or Regulus. Regulus is considered the King or Chief of the four Royal Stars. Regulus is from Rex, meaning law giver; i.e., defining order in the heavens). Regulus, however, was not always close to Earth's ecliptic plane nor at the same ecliptic longitude due to Regulus' Proper Motion.

The Galactic Equatorial Ayanamsa eliminates the issue of the Proper Motion of stars. The Galactic Equatorial Ayanamsa is referenced to the Galactic Equatorial axis of Earth's Precessional Cross. This approach is based on the spherical geometry of the astrophysical spheres involved (specifically our solar system's current location and orientation (tilt) in our galaxy / the galactic equatorial axis / Gate of God), rather than on star locations as seen from Earth. The galactic equatorial axis is far more "fixed" than the stars as seen from Earth, which move over longer periods of time.

Now, before you loyal Fagan-Bradley astrologers (or any others) scoff, please understand I am placing astrological and astronomical precedence in the geometric relationship between the vernal axis and the galactic axis over the relationship of tropical and sidereal signs. The signs are merely harmonic divisions nesting within this far more embracing astrophysical geometry. The tropical signs are based upon the moving vernal axis of this underlying geometry and the sidereal signs are based upon fixed galactic axis—thus independent of constellations, which is imagery that has evolved and changed over time, and independent of stellar placement, which also changes over long-periods.

Consider that the fixed galactic equatorial axis relates more to our durative soul-level awareness, whereas the moving vernal axis reveals the current incarnational punctual moment (our daily tropical experience), precipitating from the durative soul stream (sidereal / soul experience).

Realizing the relevance of Earth's Precessional Cross geometry (the movement and geometric orientation of our Earth and Sun in our galaxy) places the signs (and our awareness) in the far greater context of our evolutionary sojourn as a stellar race of sentient souls.

Thus, the Galactic Equatorial Ayanamsa is defined by the Galactic Equatorial Node (GEN) as being the prime fiducial of the sidereal zodiak; setting the GEN (Gate of God) to exactly 5° 00' 00" sidereal Sagittarius. The Galactic Equatorial Ayanamsa is 25° 00' 00" for epoch 2000 CE. Thus, 0° Tropical Aries resides at 5° 00' sidereal Pisces @ 2000 CE; i.e., the tropical zodiak has drifted from the fixed sidereal zodiak by 25° 00' 00" based upon the Galactic Equatorial Ayanamsa.

The placement of the sidereal signs reckoned to the Galactic Equatorial Node (Galactic Equatorial Ayanamsa) is quite close to the both the Fagan-Bradley reckoning (Spica) and the Babylonian reckoning (Aldebaran). Differences this small can become an academic argument only. However, various stars may lie on different sides of the sign cusps depending on which reckoning is used. Detailed exploration of the appropriate placement of cuspal stars is something I have explored using the Galactic reckoning, although beyond the scope of this writing. Another area where the exactness of sidereal sign cusps become of significance is when using sub-divisions of the signs (dwads, etc) where each sub-division is ruled by a specific sign. Using this astrological technique, the placement of a planet in a chart may cause it to cross a sub-cusp depending on the reckoning used. This is another interesting way to experientially explore the reckoning of the sidereal zodiak, and which ayanamsa make more sense to you.

I am not arguing the validity of any ayanamsa, nor do I have any interest in debating that there is a correct ayanamsa. I am simply providing an alternative. In addition, I tend to look at stellar qualities which change throughout each sign rather than having interest in sign-based delineations of the heavens, and thus primarily use the sidereal zodiak as a measurement system for ecliptical longitudes amongst the stars.

Something else one might consider is that it may be of interest to use a different ayanamsa for different reasons as the chosen fiducial (a specific star or whatever is used as reference) provides a unique underlying context. You can get a feel for this if you research the originator's reasoning for any specific ayanamsa.

An ayanamsa (any ayanamsa) is a dynamic figure because the vernal point (0° tropical Aries) constantly moves due to Earth's precession. Therefor, an ayanamsa must be referenced to a specific time in the precessional cycle—generally this is 1950 or 2000 CE. When converting a tropical chart to a sidereal chart, this precessional drift must be taken into account, especially if making a chart in the far distant past or future. Software programs generally take into account Earth's precessional drift and nutational variances when calculating a sidereal chart, but the sidereal astrologer must choose the ayanamsa of his or her choice. Star longitudes must be adjusted to the chosen ayanamsa if adding individual stars to an astrological chart. This is important due to the tight orb of stellar influence.

An Introdution to Astronomical Astrology & The Star Catalog

"An Introduction to Astronomical Astrology" is an entirely new edition of what was formerly "The Star Catalog," with an extensive update to the section delineating the stars and constellations as they express throughout the zodiak and in an astrological chart. This excursion through the heavens will give you an excellent foothold to star-level astrological interpretation. The star catalog section is also updated, now with over 750 stars and deep space objects.

Note: When I first published this work many years ago, I simply called my ayanamsa the Galactic Ayanamsa. Since then, there as been a proposal to use Galactic Center as an ayanamsa reference, with the originator choosing the same name, apparently unaware of my work. Thus to avoid any confusion with it, I have clarified the name of this ayanamsa to be the Galactic Equatorial Ayanamsa.

Astronomers use the Right Ascension (R.A.) and Declination (Dec.) to define star locations, which are coordinates referenced from the moving vernal point, with Right Ascension being the longitude along the Celestial Equator and with Declination being the distance above or below the Celestial Equator, not from the ecliptic. Thus an epoch of measurement must always be defined along with the R.A. and Dec. of a star due to the moving vernal point—like measuring the distance between two points while moving the ruler itself. Converting Right Ascension / Declination to a tropical ecliptical longitude thus yields a longitude referenced to the same epoch as the original astronomical coordinates—this must also be kept in mind. Further converting from R.A. and Dec. to sidereal ecliptical longitudes eliminates the changing epoch dates due to the use of an ayanamsa in the calculation—although resultant sidereal longitudes are unique to the chosen ayanamsa used.

The following chart is a comparison of several of the more common ayanamsas.


@ 2000 CE *

@ 1950 CE *

Delta **






22° 24' 25"

21° 42' 41"

-02° 35' 35"

01° 25' 52" Libra

17° 23'

07° 35' 35"

04° 24'


23° 45' 43"

23° 03' 59"

-01° 14' 17"

00° 04' 34" Libra

16° 01'

06° 14' 17"

03° 02'


23° 51' 11"

23° 09' 27"

-01° 08' 49"

29° 59' 06"

15° 56'

06° 08' 49"

02° 57'


24° 30' 01"

23° 48' 17"

-00° 29' 59"

29° 20' 16"

15° 16'

05° 30' 00"

02° 18'


24° 44' 12"

24° 02' 28"

-00 15' 48"

29° 06' 05"

15° 03'

05° 15' 48"

02° 04'


24° 47' 12"

24° 05' 28"

-00 12' 48"

29° 03' 05"

15° 00'

05° 12' 48"

02° 01'


25° 00' 00"

24° 18' 16"

00° 00' 00"

28° 50' 17"

14 ° 47'

05° 00' 00"

01° 48'


27° 48' 20"

27° 06' 36"

+02° 48' 20"

26° 01' 57"

11° 59'

02° 11' 40"

29° 00' Sco

Larry Ely

28° 00' 13"

27° 18' 29"

+03° 00' 13"

25° 50' 04"

11° 47'

01° 59' 47"

28° 48' Sco

Converting Tropical Longitudes to Sidereal Longitudes

* The Ayanamsa @ 2000 CE can be used to convert tropical longitudes to sidereal longitudes. For example if your Sun resides at 0° 00' 00" Aries (exactly on the vernal point) subtract 24° 44' 12" to get your sun's sidereal location using the Fagan-Bradley ayanamsa. Or subtract 25° 00' 00" to get your sun's sidereal location using the Galactic Equatorial Ayanamsa.

A quick and simple shortcut to this is to add 5° and drop back a sign; i.e., if your tropical Ascendant is 9° 00' sidereal Pisces (add 5°, minus one sign). Your sidereal ASC is 14° 00' sidereal Aquarius. This is only true for charts cast around 2000 CE only. Remember, an ayanamsa changes over time at the rate of precession, so this shortcut does not work for dates in the distant past or distant future. The chart above lists ayanamsas for two epochs: 1950 and 2000 CE.

Converting Longitudes using one Ayanamsa to another Ayanamsa

** The Delta figure can be used to convert sidereal longitudes calculated with one ayanamsa to those of another ayanamsa. The DELTA figure can be rounded off from “seconds of arc” to “minutes of arc” for most purposes: For example, if you have a computer program that calculates your ASC at 15° 03' sidereal Taurus (aligning with Aldebaran) using the Fagan-Bradley ayanamsa, you can subtract the delta figure of 00° 16' (- 00° 15' 48") to get the ASC at 14° 47' using the Galactic ayanamsa. Or, to convert a longitude to match Fagan-Bradley, add 00° 16'. Note that the Galactic, Babylonian and Fagan-Bradley ayanamsas vary by just a fraction of a degree, and Takra’s by just 1/2°.

To Convert Raman to Galactic subtract 02° 36' from the longitudes in your chart.
To Convert Krishnamurti to Galactic subtract 01° 14' from the longitudes in your chart.
To Convert Lahiri to Galactic subtract 01° 09' from the longitudes in your chart.
To Convert Takra to Galactic subtract 00° 30' from the longitudes in your chart.
To Convert Fagan-Bradley to Galactic subtract 00 16' from the longitudes in your chart.
To Convert Babylonian to Galactic subtract 00 13' from the longitudes in your chart.
To Convert DeLuce to Galactic add 02° 48' to the longitudes in your chart.
To Convert Larry Ely to Galactic add 03° 00' to the longitudes in your chart.

Precessional Time is NOT a Constant

To further compound the problem of zodiakal reckoning, we must recognize that the rate of Earth's precession is NOT a constant. It is accurate to say the last erect precessional cross had occurred exactly 180° degrees ago in the precessional cycle, but we can only estimate that to have been 9,000 to 13,000 years ago. The rate of precession may vary over long periods of time, or even oscillate around some harmonic ideal. There are many continuously changing astronomical factors that affect the rate of precession, not to mention the cause of the precessional of the equinoxes is not even clear. (Just as we can not pinpoint a date in the distant past is why I suggest man-made calendars made in antiquity fall short of being able to predict future evolutionary changes to a specific date.)

"The Great World Cycle," or "Earth's Great Year," as Earth's precessional cycle is sometimes called, is estimated to be between 22,000 and 26,000 solar years—most often rounded to 25,000 or 26,000 years. The 25,920 figure, sometimes seen, is a natural harmonic ideal. Another number of significance is 22,680, quite close to the 23,000 figure. These are all academic figures however: Earth's current rate of precession is calculated to be ~25,867 years, and it is slightly increasing. This is a precessional rate of 1° every ~71.85 years, or 0° 00' 50.26" per year.

Walter Cruttenden, in his binary star model, suggests our binary sun's average orbital period is 24,000 years, with it slowing to 22,000 years or less at the binary orbit's apoapsis and increasing to 26,000 years at its periapsis. This model appropriately recognizes an ever changing precessional rate.

Some Technical References on Precession & Earth Orientation:

ECLIPTIC - Celestial Mechanics and Dynamical Astronomy (2006) (PDF)

IERS (International Earth Rotation & Reference System Service)

Earth Orientation Centre

JPL Technical Report Server

Related Material

The Heptanomis

Earth's ~25000-year polar precessional circle inscribed in the heavens, also called the polar arc, is naturally divided into seven evolutionary epochs called the Heptanomis—also referred to as the seven heavens, mansions, and the seven days of creation.

View the Heavens: Under the Stars

Getting to know the heavens: This link is to a star chart the heavens that shows the individual stars, constellations, and the sidereal signs. Visually learn how the stars and constellations interrelate and blend to create each sidereal sign. This is a wonderful tool for the novice or seasoned astrologer, for the astronomer, for the casual sky watcher, or simply for those who wish to know more of the Greater Heavens under which we live. The Sky Chart is also a wonderful reference for the material presented in each month's Lunar Planner. You can also see the celestial equator and the galactic equator, the contellations they pass through and their nodes.

Personalized Star Charts

Sample Star Chart

This made to order star chart of the sidereal heavens shows where the planets and asteroids were at the time of YOUR birth.

Visually learn which stars conjoin your natal planets; and see where they reside in the constellations and sidereal signs.

Learn about your Horizon Plane, Meridian, and Prime Vertical, how these great circles create your Personal (Natal Cross), and how that cross nests upon Earth's Precessional Cross—all creating your personal sacred geometry.

This is your personal astronomy from which an astrology chart is derived. The great circles in this chart create your Ascendant, Descendant, Mid-heaven, Anti-Mid-heaven, Zenith, Nadir, East Point, and Vertex. Your Personalized Star Chart reveals exactly where these great circles and points lie in the heavens, and which stars and constellations they align with. This chart will provide insight into your greater self for years to come—and it prints as a beautiful high-resolution poster.

Personalized Star Charts