A 13th Zodiac Sign? It’s Your Choice

The traditional 12 signs or constellations of the zodiac

So I find out this morning that a 13th sign has been added to the zodiac.


A Minneapolis Star Tribune story earlier this week about zodiac signs quoting Minneapolis astronomer Paul Kunkle saying (correctly) that when astrologers say the sun is in Pisces, it isn’t. Kunkle also mentioned that the sun spends more time in the constellation Ophiuchus the Serpent Bearer than in the neighboring traditional zodiac constellation Scorpius. Also true. To be fair then, shouldn’t Ophiuchus be brought into the zodiacal fold as the 13th sign? Since the story first appeared, the Internet has been abuzz with folks wondering whether they should upgrade their “sign” and check out their Serpent Bearer potential.

Back in the olden days circa 1000 B.C., the Babylonians divided up the circle of the sun’s yearly path across the sky into 12 approximately equal constellations for the 12 months of the year. This system came down to us through the Greeks as the zodiac. Your sign is determined by which of the 12 constellations the sun was in on the date of your birth. My birthday is August 9, which makes me a Leo, named for the constellation Leo the Lion. Well and good … 2000 years ago.

Precession causes Earth’s axis to trace out a circle against the backdrop of stars in the span of 26,000 years. Credit: NASA

Enter a little thing called precession. Earth’s axis slowly wobbles or precesses over a period of 26,000 years due to the combined gravitational tugging of the sun and moon. Picture a spinning top slowing down. As its spin rate drops, the axis of the top describes a little circle (wobble) in the air before eventually tipping over. The Earth’s axis describes a similar circle in the sky with a period of 26,000 years. Since the pole star is determined by where our axis points, it follows that we see a variety of different pole stars during that long cycle. Right now, Polaris in the Little Dipper sits in the hallowed spot at which our axis points, but in 14,000 A.D., brilliant Vega will occupy the position. Due to the cyclic nature of precession, Polaris will regain its North Star title in 28,000 A.D.

At the same time that the pole star is slowly shifting, precession also causes a shift in the background constellations against which the sun appears to move. Keep in mind, the constellation outlines remain the same; it’s where the sun is in relation to the background stars that changes.

The Earth’s wobble causes the sun to drift westward along the zodiac to the tune of 1.4 degrees (about three sun diameters) per century. In 2,000 years, that adds up to 28 degrees or about one zodiac constellation width.

Precession not only shifts the pole star, but also makes the sun appear to drift westward against the background constellations along its yearly path called the ecliptic. You can see that 2000 years of precession has moved the sun’s mid-January position from Capricornus to Sagittarius. Note: I’ve subtracted the Earth’s atmosphere so you can see where the sun is among the daytime stars.  Illustrations created with Stellarium

Let’s look at an example. Since the year 1 A.D., the Earth’s wobble has caused the sun to slide westward a full constellation. Back in the glory days of Rome on January 14, the sun was in Capricornus. 2000 years later we see it in Sagittarius. 2000 years from now its westward excursions will take it into Scorpius.

The ancients were aware of precession’s effects, but today’s astrologers choose not to update their signs. As a result, the sign you were born under is only correct for a limited period of time, maybe 1000 years, give or take. My birthday sign is no longer Leo but Cancer, the zodiac constellation to the west of Leo.

Below is a listing of new dates when the sun’s in your sign based upon its true location in the sky. I’m certain it will never be adopted. Tradition you know.

* Sagittarius: Dec. 17-Jan. 20. Capricornus: Jan. 20-Feb. 16. Aquarius: Feb. 16-March 11. Pisces: March 11-April 18. Aries: April 18-May 13. Taurus: May 13-June 21. Gemini: June 21-July 20. Cancer: July 20-Aug. 10. Leo: Aug. 10-Sept. 16. Virgo: Sept. 16-Oct. 30. Libra: Oct. 30-Nov. 23. Scorpius: Nov. 23-29. Ophiuchus: Nov. 29-Dec. 17. 

Based on modern constellation boundaries, the sun now officially spends nearly three weeks a year in Ophiuchus, more than twice as long as it does in neighboring Scorpius. The sun’s position is shown for Dec. 12.

Ophiuchus is included just for fun as the 13th sign. Ophiuchus wasn’t even a contender for a zodiac sign back when the system was created, because the obvious outline of its stars lay to the north of the sun’s path. The sun started crossing Ophiuchus in 1930 when the International Astronomical Union officially fixed the current constellation boundaries. In doing so, they included a nondescript chunk of sky below the constellation’s main outline within the official border. The sun travels through this bit of celestial real estate in late November-early December en route from Scorpius to Sagittarius.

So what do you think? Should astrologers update the zodiac every 500 years or so to keep the sun in its rightful place? For me, it doesn’t matter either way since the positions of the sun, moon and planets have no bearing on either my personality or fate. That stuff’s in other hands.

15 Responses

  1. jeff

    are people really buying this non sence?? i want you to take the new sign and research the true meaning of the symbolizim within it. add it up

    1. astrobob

      Jeff, Ophiuchus has been around a long time. It was one of the original 48 described and handed down in around 100 A.D. It’s visible during the summer and has lots of great telescopic sights.

  2. Rhonda

    How do the reports that the axis of the earth has been shifted a couple inches by recent earthquakes affect all this? Not to mention other earth shifting events in years gone by….

    1. astrobob

      Hi Rhonda, good question. The earthquakes are an occasional and a minor blip compared to the steady, if slow, cycle of precession. Now if the Earth got whacked by large asteroid, that could make a significant difference in rotation rate and even the tilt of the axis. Chances of that happening are thankfully remote!

  3. Bob, When the earth ‘wobbles’ in it’s axis, does that actually affect the distance that the earth is from the sun in terms of the Northern or Southern Hemisphere? In other words, does it change the degree of tilt? I am asking because I am wondering if this might be a partial explanation of the change in surface temperatures?

    1. astrobob

      Hi Mamamia,
      Thanks for asking. Precession does not affect the tilt of the axis – it’s still 23.5 degrees. The axis just rotates around a circle without changing its angle. It also doesn’t affect the distance between the Earth and the sun. That distance varies over the year by a small amount because the Earth’s orbit isn’t circular but elliptical (oval). The planet is 3 million miles closer in winter than in summer. Even that has little effect on our climate for a couple reasons I explained in this earlier blog: http://astrobob.areavoices.com/2011/01/04/cool-meteor-animation-and-a-day-to-feel-closer-to-the-sun/

  4. Alexis

    Very interesting – as an extremely amateur astrologer I have always wondered what the current consensus is on this subject and how it is exactly astrology has altered itself according to a changing sky over that last few thousand years. Would love to see comments by active astrologers. As for the addition of Ophiuchus, in keeping with more regular cycles and “tradition” I would tend to exclude it from the zodiacal calendar.

    1. astrobob

      I agree about Ophiuchus, Alexis, even as an amateur astronomer. It’s a modern convention and needn’t play a part.

  5. stormchaser

    I’m not going to switch signs because I have too many Libra items. The socks and shirts I can replace, but I’m not driving all the way to Ross in Denver to find a new aluminum water bottle. lol

  6. poornakumar

    Better shift the area of Ophiuchus [visible stars theta, 44, 45, 36 (or 6402), 36 (or 6401), omicron, 43, 24, 26, (6308), rho & (4694)], redesignate as Scorpio including the line of Ecliptic. It is needed for the sake of elegance and to preserve the ancient format (else why should we name stars as Greek and Roman?). Heavens aren’t going to fall (by Belenos). Eugene Delporte when he did this boundary drawing should have paid attention to this aspect. He didn’t and don’t know why.

  7. Kelly

    Hello! I was born in 1995, so does this effect me? I originally Aquarius, my birthday is February 10, but now am I changed to a Capricorn? If so, my personality, fortune and who my compatability is changed right? Thanks I am really confused.

    1. astrobob

      Hi Kelly, I wouldn’t worry about this. Changes in the sun’s position in the zodiac as well as Ophiuchus becoming a member of the zodiac are recognized and acknowledged in astronomy. Astrology is something else altogether. It’s not tied to scientific fact or proof and has its own set of guiding principles. I think you can safely count on staying an Aquarius.

  8. Tom Ruen

    Good discussion. I had questioned my astrologer friends about this difference for years, and never got a clear answer.

    So with the new drama I found two terms on wikipedia now that offer both interpretations.
    Astrology by fixed stars (constellations)
    Astrology by season/calendar dates:

    And I agree Ophiuchus is just a distraction, due to the boundary definitions of astronomers, apparently in 1922.

    It is all funny. Astrologers love the planet pluto too, dancing many degrees off the ecliptic, and smaller than our moon. I wonder if they worry if it is a planet?

    It is sort of nice to be able to talk with astrologers and pretend we have a common interest in astronomy, but it is annoying if they say “Saturn is in X” and it looks like Virgo to me. Maybe I’ll have to add astrological Zodiac boundaries to my astronomy software so I can translate more efficiently!

  9. Leone Tamminen

    What exactly is a horoscope? You have to understand that is basically where the stars and planets are positioned in certain time frames. You will find that many of astrologers will make a chart and it will stay a lot about who you are and why you are who you are. As for the horoscope chart, you will find that the wheel is separated into twelve parts and it has many symbols drawn on it to represent things like the planets and the stars. You will also find that there are many horoscope signs, but each one is unique in its own way.,

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