Last January a Minneapolis astronomy professor caused an uproar when he alleged that everyone’s sun sign had changed due to a ‘new’ 13th zodiac sign, Ophiuchus. A few weeks ago I saw evidence of this rumor still alive and well on the Internet, so I’d like to help set the record straight.
There is no 13th sign, nor is there a need for one. The 12 we already have do the job just fine.
Where does this idea of a 13th sign come from? To understand this, we have to sort out two issues: the tropical vs. sidereal zodiac, and signs vs. constellations.
The tropical zodiac is a division of the ecliptic (the apparent path of the Sun across the sky around the earth) into twelve equal parts of 30 degrees each, anchored at the equinoxes and solstices and correlating perfectly with our four seasons:
• Vernal equinox = Spring = Sun enters 0 degrees Aries;
• Summer solstice = Summer = Sun enters 0 degrees Cancer;
• Autumnal equinox = Fall = Sun enters 0 degrees Libra;
• Winter solstice = Winter = Sun enters 0 degrees Capricorn.
The sidereal zodiac is a division of the ecliptic into twelve equal parts of 30 degrees each, anchored at one or another of the fixed stars (called “fixed” because they appear not to be moving, vs. the “wandering” planets in our solar system). There are several variations of the sidereal zodiac in use, the most common being the Lahiri, which places 0 Libra at the fixed star Spica.
There is currently a difference of about 24 degree between the two zodiacs. Spica in the tropical zodiac is measured at 24 Libra.
Why the big difference? The answer is precession. Precession is an apparent drifting backward (westward) of the constellations at the rate of one degree every 72 years due to a “wobble” in the earth’s axis. There was a time, about 1800 years ago, when the two zodiacs were in sync.
To confuse things even further, some say the zodiac signs should not be evenly distributed but should correlate perfectly with the stars exactly as they appear in the sky today. That would give us some enormous signs (like Virgo) and some very small ones (like Scorpio).
So what is the difference between a constellation and a zodiac sign?
A constellation is defined as a cluster of stars in the heavens perceived as a figure or design. There are 88 constellations officially recognized by astronomers. Some of these constellations fall on the ecliptic, hence their inclusion in the zodiac. Because of precession, however, the signs as we know them and the constellations as they now appear in the sky are out of sync. Remember, though, that the tropical zodiac is perfectly in sync with the seasons which define our lives.
So what about Ophiuchus? Ophiuchus is a constellation. The stars which comprise Ophiuchus (or any other constellation) can be important for an individual if found in a significant place in the natal chart--at one of the four angles, or on a house cusp, or conjunct one of the seven planets. The alpha star of Ophiuchus, Rasalhague, lies at about 22.34 degrees of Sagitattarius at present (in the tropical zodiac).
But Ophiuchus is not a sign, nor will it ever be.
Modern astrology as it is popularly (mis)understood places way too much emphasis on “what sign you are” to begin with.
But that is a subject for a different post!