Astrology and Horoscopes

Constellation Ophiuchus

Ophiuchus – a 13th Zodiac Sign? No!

Signs and Constellations: The Origin of the Illusory ‘Thirteenth Sign’ Debate


Astrology and astronomy, once twin sciences, have followed divergent paths since the Age of Enlightenment. Astronomy moved towards a positivist view of the cosmos through the work of Brahe, Kepler, Newton and others. Astrology, although probably practiced by Brahe and Kepler, was lost from the mainstream of western learning from this time. In modern times, astrology has wound a tortuous path through mysticism, esotericism, psychology and, during the 1980s and 1990s, a recovery of its own theoretical and practical past to arrive at a crossroads in the first years of the twenty-first century.

Since its isolation from mainstream intellectual thought, astrology has become a laughing stock for many scientists who maintain a rigidly materialist view of the world. Astrology does not easily allow scientific or statistical experimental methods to explore its knowledge. Only one statistician/astrologer, Michael Gauquelin, working in France between the 1950s and 1980s, has had any success at establishing astrological correlations. His work – most famously known for the ‘Mars Effect’ – supported some of the central principles of astrological thinking, but failed to support many of the techniques employed by practicing astrologers.

Two fundamental criticisms have been levelled at astrologers in recent years. The first is that they do not understand the notion of precession of the equinoxes. The second is that they have failed to take account of the true nature of the zodiac. This last criticism has become known as the ‘thirteenth sign’ argument on the basis that the zodiac actually contains thirteen rather than twelve signs.

Those that mount the argument claim to have established that astrology cannot possibly be true because the ecliptic has thirteen constellations around its 360 degrees. Since astrological method only recognises twelve signs (Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius and Pisces) it is fatally flawed. The intruder sign, Ophiuchus, a constellation occupying a portion of the ecliptic between Scorpio and Sagittarius, is the mysterious ‘thirteenth sign’ that astrologers appear to omit.

An Important Note

All the ideas in this article refer to a western astrological perspective. This astrological method uses a fixed or tropical zodiac – one that is derived from the seasonal variation in the Earth’s path around the Sun in relation to the plane of its own rotational axis. The Indian Vedic tradition uses a sidereal or corrected zodiac and is conceptually independent of the western system. Both forms of astrology use the same planets and Sun and Moon. (In general, within the Vedic tradition, only the visible planets are used.)

This author has very little experience of the sidereal method and is unable to comment on the theoretical or practical validity of a sidereal zodiac. However, the tropical method has a conceptual rigour and simplicity which the author finds compelling. All references to seasons or seasonality assume a northern hemisphere perspective. However, the phenomenon of the Equinoxes – the Sun’s apparent crossing of the Celestial Equator – is hemisphere independent. All terms are defined below.

Signs and Constellations

At the root of the the ‘thirteenth sign‘ debate is a confusion that exists in the minds of astronomers and many astrologers. It is the assumption that zodiacal constellations, recognised by astronomers, are identical with the zodiacal signs, recognised by astrologers. Very few prominent astrologers, except perhaps Dane Rudhyar, have been absolutely clear that zodiacal signs – Aries to Pisces – are not the same as zodiacal constellations (which include Ophiuchus).

The confusion between signs and constellations also touches on the other criticism that has been used to attack astrology. This second criticism is based on the assumption that astrologers do not understand the phenomenon of precession of the equinoxes – the backward motion of the Vernal Equinox through the zodiac over a period of about 26000 years. Although the ‘thirteenth sign’ debate and the precession objection are not obviously linked, they are, in fact, part of the same confusion that has undermined the credibility of astrology since the Age of Enlightenment.

Jacqueline Mitton, an astronomer, sums up the problem succinctly: “The band of constellations through which the ecliptic passes defines the traditional zodiac, though the effects of precession and the precise definition of the constellation boundaries mean that the ecliptic now passess through an additional constellation, Ophiuchus.” (Mitton, 1993, p. 129)

Ophiuchus is a constellation of stars visible in the northern hemisphere between the constellations of Scorpio and Sagittarius. Depending on where one considers the boundaries of the constellations to lie, it may be considered to intersect those two constellations. In such a case, the Sun, the Moon and the planets, during the course of their apparent passage through the constellations, will pass through Ophiuchus after leaving Scorpio and before entering Sagittarius.

However, there is no such thing as a zodiacal sign called Ophiuchus. There is no way that your sun or star sign could be Ophiuchus. Let me explain further.

Ancient and medieval astrologers considered that there were 48 constellations. Of these, 12 were considered ‘zodiacal’ constellations, the other 36 were considered ‘extra zodiacal’ constellations. The 12 zodiacal constellations are those through which the Sun appears to pass during the course of a year, and their names (Aries through to Pisces) are familiar to anyone interested in his or her sun or star sign.

Ophiuchus is one of the 36 extra zodiacal constellations – not one of those through which the Sun is considered as appearing to pass.

The ancient world delineated three zodiacs.

  • First, the Constellational Zodiac. This comprises the 12 constellations familiar to us as zodiacal, these 12 being of unequal length.
  • Then there are the Sidereal Zodiac and the Tropical Zodiac, each comprising 12 signs of equal length.
  • The Sidereal Zodiac is a regularization of the Constellational Zodiac to make 12 signs of equal length out of 12 constellations of unequal length. Note that even in so-called ‘sidereal’ astrology, the sign in which the Sun is considered to be may not be the same as the constellation through which it is passing, due to the unequal size of the constellations.

The difference between sign and constellation is more pronounced where the Tropical Zodiac is used (as is normal in western astrology). Whereas the Sidereal Zodiac is a division of space, the Tropical Zodiac is a division of time, and is related to the seasons. Where the Tropical Zodiac is used, the Sun is considered to enter the sign Aries at the northern Vernal (or Spring) Equinox (around March 21/22) no matter what constellation it is apparently passing through at the time.

At around the year 0 (the beginning of the Christian Era) the Sidereal Zodiac and the Tropical Zodiac coincided. Whichever zodiac one used, the Sun entered the sign Aries at the same time. However, due to a phenomenon known as the Precession of the Equinoxes, the Sun at the northern Vernal Equinox has since then been drifting back through the Sidereal sign Pisces. When the Age of Aquarius arrives (there is no consensus as to the date) the Sun will be in the Sidereal sign Aquarius at the northern Vernal Equinox. But from the point of view of astrologers who use the Tropical Zodiac, the Sun will still enter the sign Aries at this Equinox.


Mitton defines a constellation as “one of 88 designated areas in the sky or the pattern of stars within it.” (Mitton, 1993, p. 88) The boundaries of the constellations have been subject to change over the course of astronomical learning. The origins of the constellations are lost in time, but it may be that the original astrologer/astronomers recognised only the constellations on the main belt of the ecliptic. The boundaries of the constellations were most recently defined in 1930 using lines of right ascension and declination. Constellations vary in area – some occupy extraordinarily large areas of the sky; others are relatively small. The constellations that cross the ecliptic (or zodiac) occupy unequal portions of the ecliptic. In other words, the zodiacal constellations do not divide the ecliptic equally, unlike the zodiacal signs.

Precession of the equinoxes is the result of precession – “the uniform motion of the rotation axis of a freely rotating body when it is subject to turning forces (torque) due to external gravitational influences.” (Mitton, 1993, p. 306) In essence, the gravitational effect of the Sun and the Moon on the Earth causes the Earth’s rotational pole to move around the pole of the ecliptic over a period of 25800 years. This has the effect of causing the Vernal Equinox, or First Point of Aries, to move backwards through the zodiacal constellations. The Vernal Equinox currently lies in the early degrees of the constellation called Pisces.

The Vernal Equinox is one of a pair of equinoxes. An equinox is defined as “either of the two points at which the celestial equator intersects the ecliptic, and also the times when the Sun passes through either of these points.” (Mitton, 1993, p. 141) The other equinox is the Autumnal Equinox. At the Vernal Equinox the Sun is passing from south of the celestial equator to north of the celestial equator. At the Autumnal Equinox, the Sun is passing from north to south. The passage of the Sun through these points, and the Solstices, defines the four seasons of the year. This point will be very important when we consider Rudhyar’s arguments. It should be noted that the above definitions of the Vernal and Autumnal Equinoxes represents a northern hemisphere perspective.

A zodiacal sign is one of twelve equal divisions of the ecliptic derived from the Vernal Equinox or the First Point of Aries. A zodiacal sign occupies thirty degrees of celestial longitude. Thus the first thirty degrees of the ecliptic from the Vernal Equinox make the sign ‘Aries’; the following thirty degrees of the ecliptic are the sign ‘Taurus’; the third thirty degrees are the sign ‘Gemini’; and so on. Mitton acknowledges this in her definition of the zodiac: “In traditional astrological use, the zodiac is divided into twelve equal 30 degree portions, each of which is allocated to a ‘sign’, but these do not correspond exactly to the astronomical constellations, which are of varying sizes.” (Mitton, 1993, p. 416)

The ecliptic is “the mean plane of the Earth’s orbit around the Sun.” (Mitton, 1993, p. 129) The Earth passes around the Sun once a year. Astrologer’s often talk as if the Sun moves around the Earth in an annual cycle, and that the Earth is the stationary point. However, this point of view simply reflects the observational reality described by Mitton: “From the point of view of an observer on Earth, the relative orbital motion of the Earth and Sun makes it look as if the Sun were travelling around the Earth once a year.” (Mitton, 1993, p.129) Astrologers do not believe that the Sun moves around the Earth.

The celestial equator is the plane of the Earth’s rotation projected onto the celestial sphere. It marks the boundary between the northern and southern hemispheres of the celestial sphere.

You may check these definitions against the diagram below.

Figure 1: Showing the Relationship Between Equator and Ecliptic and the Twelve Astrological Signs

Figure 1: Showing the Relationship Between Equator and Ecliptic and the Twelve Astrological Signs

In this diagram, the twelve zodiacal signs are shown on the ecliptic. The first sign, Aries (Ar) commences at the First Point of Aries or the Vernal Equinox, and occupies thirty degrees of the ecliptic. It is followed by the second sign, Taurus (Ta); this sign occupies the second thirty degrees of the ecliptic. The third sign is Gemini (Ge). The Summer Solstice marks the Sun’s highest northerly declination (about 23 1/2 degrees north of the celestial equator). In astrological terms this marks the beginning of the fourth sign Cancer (Ca). The opposite point, the Winter Solstice, marks the Sun’s most southerly declination (about 23 1/2 degrees south of the celestial equator). This point marks the beginning of the tenth sign Capricorn. The seasonal references imply a northern hemisphere perspective on this annual cycle of the Sun.

The Thirteenth Zodiac Sign – Ophiuchus: The Astronomer’s View

The redoubtable Patrick Moore says of the thirteenth sign: “Ophiuchus intrudes into the Zodiac between Scorpius and Sagittarius – to the fury of astrologers, who devoutly wish that the Serpent-bearer did not exist!” (Moore, 2001, p. 212) Moore is presumably referring to the fact that astrologers work with twelve zodiac signs: Ophiuchus, being the thirteenth constellation to cut the ecliptic, destroys this principle at a stroke, or so it appears.

However, Mitton has made it clear that the signs and constellations are not the same thing. Dane Rudhyar, one of the principle astrologers of last century, was also very clear about this distinction. Any argument aimed at undermining astrology based on the failure to incorporate Ophiuchus into the astrologer’s zodiacal lexicon must take account of this difference. It is simply not enough to point out that the constellation Ophiuchus cuts the ecliptic and creates a ‘thirteenth sign’. Zodiacal signs and zodiacal constellations are not equivalent.

Rudhyar’s Insight

Dane Rudhyar is one of the few prominent astrologers to make the distinction between signs and constellations absolutely clear in his work. Many of his writings include references to this distinction. At times, the difference between signs and constellations is at the heart of Rudhyar’s symbolism and technique. For example in the The Pulse of Life writes at some length of his understanding of the difference between zodiacal signs and zodiacal constellations.

“The Zodiac which is used in our astrology has very little, if anything at all, to do with distant stars as entities in themselves. It is an ancient record of the cyclic series of transformations actually experienced by man throughout the year; a record written in symbolic language using the stars as a merely convenient, graphic way of building up symbolic images appealing to the imagination of a humanity child-like enought to be more impressed by pictures than by abstract and generalised processes of thought. The essential thing about the Zodiac is not the hieroglyphs drawn upon celestial maps; it is not the symbolical stories built up around Greek mythological themes – significant as these may be. It is the human experience of change.” (Rudhyar, 1970, p. 21-22.)

And again, in The Practice of Astrology, Rudhyar spells out in extremely clear terms, the distinction between signs and constellations as he sees it (and takes astrologers and sceptics to task for not having understood the difference):

“…the majority of devotees (and of the critics) of astrology have not yet understood that the signs of the zodiac have nothing to do whatsoever with actual stars and constellations, but are simply twelve phases of the cyclic relationship between the earth and the sun.” (Rudhyar, 1968, p. 38)

What Rudhyar is saying is that at the heart of Western astrological practice and understanding is the fundamental distinction between zodiacal signs and zodiacal constellations. The Western astrologer is using a division of the ecliptic that is based on twelve equal portions of thirty degrees each; the first portion begins at the northern Vernal Equinox or the First Point of Aries.

Elsewhere Rudhyar laments that the unfortunate fact that the signs and constellations share the same names. This, of course, tends to reinforce the misleading viewpoint that they are identical. Perhaps astrologers would do well to rename the signs with alternative titles to force the distinction into wider consciousness.

The Thirteenth Zodiac Sign – Ophiuchus: The Astrological View

The astrological chart below is provided to make the distinction between signs and constellations clear in a visual way. Note that the inner coloured band represents twelve zodiacal signs each of thirty degrees of zodiacal longitude. The outer coloured band is a graphical representation of the constellations showing the proportion of the ecliptic that they actually occupy.

Figure 2: Showing the Relationship Between Zodiacal Signs (Inner Band) and Zodiacal Constellations (Outer Band) On the Ecliptic

Figure 2: Showing the Relationship Between Zodiacal Signs (Inner Band) and Zodiacal Constellations (Outer Band) On the Ecliptic

This diagram shows the relative sizes and positions of the signs and constellations on the Ecliptic. It is based on an astrological representation of the heavens for the moment of the Lunar Eclipse in November 2003 set for Exeter, England. The inner band shows the twelve zodiacal signs of equal longitude. The outer band shows the actual sizes of the constellations on the Ecliptic. Note Ophiuchus between Scorpio and Sagittarius – the white portion of the outer band.

Note the beginning of the sign Aries (shown by the symbol that looks like a fountain on the righthand side of the chart) in the early degrees of the constellation Pisces (shown by the symbol that looks like chain links). This reflects the movement of the Vernal Equinox through the constellations due to the phenomenon of precession. Note the placement of the planet Jupiter in the sign of Virgo (on the lefthand side of the chart) but in the constellation Leo (shown by the curly lion’s mane symbol).

If you look up into the sky at this time in Exeter (assuming clear skies) you will see the Moon just west of due south in the constellation of Aries. (The Moon will be glowing red due to the eclipse shadow); bright Saturn will be just east of south in the sky in the constellation of Gemini; and Jupiter will be rising over the eastern horizon in the constellation of Leo. (It may be quite difficult to see until it rises higher in the sky.) However, note that an astrologer would describe the Moon in the seasonal zodiacal sign of Taurus, Saturn in seasonal Cancer and Jupiter in seasonal Virgo. These astrological positions are based on the placement of the bodies relative to the Vernal Equinox rather than relative to the background of stars and constellations.

The Astrological Rationale

The rationale employed by astrologers to justify the twelve-fold division of the ecliptic into zodiacal signs is essentially based on a metaphysical point of view. The division of the ecliptic into quarters is obvious enough: it gives us the four seasons beginning with spring and ending with winter. The further division into twelve is based on the metaphysical concepts associated with the numbers two and three.

Metaphysically, the number two is associated with matter and feminity – in the broadest terms ‘yin’ qualities. The number three is associated with spirit and masculinity – in the broadest terms ‘yang’ qualities’. This dialectical relationship between yin and yang, or two and three, gives rise to the multiples of these numbers which lead to the twelve-fold division of the ecliptic.

Quantitavely oriented cientists and thinkers will, of course, struggle with the metaphysical nature of this argument. Much of the logic underlying astrology is based on qualitatively derived principles. However, this article is not really designed to lay out the metaphysical underpinnings of astrology because it would take many pages of densely argued text to do this.

It is worth pointing out however, that the underlying principles of Western astrology share much with the cultural perspective of Taoism. This lends a cross-cultural credence to the metaphysical core of Western astrology and its basis in the numbers two and three. The Tao Te Ching, a classic text embodying ancient Chinese Taoist wisdom contains the following Chapter:

The Tao gives birth to the One: The One gives birth to the two; the Two give birth to the three – The Three give birth to every living thing. All things are held in yin and carry yang: And they are held together in the ch’i of teeming energy. (Tao Te Ching, 1994, Chapter 42)

The protean nature of life arises from the transcendental unity of Tao – the source of all meaning and being which is beyond comprehension. From the purity of Tao, life becomes manifest (One) through the principles of yin (matter – Two) and yang (spirit – Three). The Zodiacal signs are a way of attempting to understand the endless round of life and death; the birth from Tao and the return to Tao. Rudhyar has the final word:

The zodiac is the formative realm of life in which the astrological Sun operates as the fountain-head of all life-processes. It is the realm of birthing, growing, maturing, decaying and dying; where substance is made and unmade; where anabolic and catabolic forces (light and shadow, integration and disintegration) operate in intense, unceasing, dynamic being. (Rudhyar, 1968, p. 42)

Key Points

The following key points summarise the main content of this article Ophiuchus – a 13th Zodiac Sign?  and the fundamental conclusions of the arguments.

  • Zodiacal signs are not equivalent to zodiacal constellations.
  • Ophiuchus, which forms a thirteenth zodiacal constellation, does not undermine the validity of a twelve sign tropical or fixed zodiac.
  • Any argument that attempts to undermine astrology’s validity on the basis of Ophiuchus’ occupation of a number of degrees of the ecliptic fails because it does not acommodate the distinction between signs and constellations.
  • Astrologers are aware of the phenomenon of precession but it is not relevant to the concept of a tropical or fixed zodiac.
  • Astrologers working within the western tropical tradition described above, are employing a twelve sign zodiac defined by the relationship between the plane of the Earth’s rotation – the Celestial Equator – and the path of its annual journey around the Sun – the Ecliptic.
  • The tropical or fixed zodiac begins at the First Point of Aries, or the northern Vernal Equinox, and divides the ecliptic into twelve equal portions.
  • The tropical or fixed zodiac reflects the division of the year into four ‘seasons’ or quarters. This has validity whether one lives in the tropics or temperate zones because the seasons are described by the annual cycle of the Sun’s relationship to the Celestial Equator.
  • Astrologers do not believe the Sun moves around the Earth in reality. However, they do believe that the apparent annual movement of the Sun along the Ecliptic, and the experiential phenomenon of the Earth’s ‘geocentricity’ within the celestial sphere, are fundamental to our awareness as human beings.


This article Ophiuchus – a 13th Zodiac Sign? No! has attempted to clarify a fundamental misunderstanding that has plagued the relationship between astronomers and astrologers for many years. It has attempted to describe how astrologers divide the zodiac into signs rather than constellations. This does not mean that astrologers do not recognise constellations, but that they work principally with a seasonally derived division of the ecliptic known as the tropical or fixed zodiac. This zodiac is based on twelve equal divisions of the ecliptic based on the original point of the Vernal Equinox or the First Point of Aries.

Astrologers do recognise and understand the phenomenon of precession. The Vernal Equinox, marking the start of the zodiacal sign of Aries, is now moving through the early ecliptic degrees of the constellation of Pisces. However, this does not invalidate the concept of the tropical or fixed zodiac which is based on the First Point of Aries. This twelve-signed zodiac, reflecting the experience of the changing seasons on Earth and the annual cycle of our planet around the Sun, still has meaning. The zodiac is called ‘fixed’ because it is based on the fixed point of the Vernal Equinox, irrespective of the position of this point in relation to the stars and constellations.

In short, the Sun still appears to cross the Celestial Equator at the Vernal Equinox whether the Equinox is in the constellation of Aries or Pisces or Aquarius. This crossing point – defining the relationship of the Earth’s plane of rotation to its annual path around the Sun – establishes the zodiacal signs and one element of the astrologer’s conceptual framework.

From time to time modern astronomers, either ignorant of the difference between the zodiacs or wishing to pour scorn on astrologers, like to point out the discrepancy between the sign a planet is said to be in and the constellation through which it is passing, or to claim that Ophiuchus is a sign that astrologers are ignoring. Both the existence of Ophiuchus and the Precession of the Equinoxes have been known about and taken account of for hundreds of years. Ophiuchus is just one of many constellations that are not included amongst those named as signs. Neither in the Sidereal Zodiac nor in the Tropical Zodiac is there a zodiac sign called Ophiuchus.


J Mitton (1993) The Penguin Dictionary of Astronomy. Harmondsworth: Penguin Books.

P Moore (2001) Phillip’s Guide to Stars and Planets. London: Chancellor Press.

D Rudhyar (1968) The Practice of Astrology (As a Technique in Human Understanding). Baltimore: Penguin Books Inc.

D Rudhyar (1970) The Pulse of Life: New Dynamics in Astrology. Berkeley: Shambala.

Tao Te Ching (1994) Tr. Man-Ho Kwok, Martin Palmer, Jay Ramsay. Shaftesbury, Dorset: Element Books.