Date: April 24, 2010

Title: Ophiuchus- the 13th Sign of the Zodiac


Podcaster: Mike Simonsen

Organization: Simostronomy blog –
Slacker Astronomy –

Description: Are you sure you know what astrological sign you are? You might be an Ophiuchan.

Bio: Mike Simonsen is one of the world’s leading variable star observers. He works for the American Association of Variable Star Observers as Development Director and heads the organization’s Cataclysmic Variable Section. He writes the astronomy blog, Simostronomy, contributes articles to Universe Today and Sky and Telscope, and is a member of the Slacker Astronomy podcast. Author of several peer-reviewed papers on cataclysmic variable stars, Mike gives talks on stellar astronomy and variable star science for astronomy clubs, science organizations and university groups throughout the United States. Mike’s observatory houses two 12″ LX200 telescopes, one for visual use and one for CCD observations, or as Mike likes to joke, “One for each eye!”

Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by Tom Foster.


Hi, I’m Mike Simonsen. Today I’m going to talk about what happens when the superstitions of astrology collide head on with the facts of astronomy.

If asked, most people can tell you what their “sign” is. They’ll tell you Gemini or Scorpio, or if you ask me- ‘Caution: rough road ahead.’ Few people actually know what it means though. Their ‘sign’ is actually their ‘sun sign’, the constellation of the Zodiac the Sun appears to reside in at the moment of their birth.

The truth is, that special solar alignment with the stars might have been true 2600 years ago, when Babylonian astrologers started making this stuff up, but it isn’t true any more.

First, the dates the Sun spends in each constellation each year have shifted by a few weeks. The Sun’s 21st century position against the background stars has shifted by as much as two constellations from its position noted by astrologers in the 5th century B.C. For example, in their time, the Sun was in front of the stars of Gemini during the first two weeks of May. Now the Sun is in front of the stars of Aries during the same two weeks. So what happened?

The earth’s axis, the imaginary line you draw from the south pole to the north pole, around which the earth rotates, is wobbling very slowly over time; like a top that is slowing down. This wobbling is called precession, and it’s so slow that the earth takes 25,800 years to complete one wobble. During this time, the positions of stars as measured in the equatorial coordinate system slowly change. This change is due to the change of the coordinates caused by precession, not the motion of the stars themselves.

The affect it has on the positions of the stars is called “precession of the equinoxes”. Over time, the position of the sun on the first day of spring, the vernal equinox, slowly drifts around the sky. Five thousand years ago the sun was in Taurus, near the Pleiades star cluster, on the first day of spring. Nowadays, the Sun is in the constellation Pisces. Six hundred years from now the sun will be in Aquarius as spring begins. This will of course signal the beginning of the fabled Age of Aquarius, a time of universal peace and brotherhood, if you believe in that sort of thing.

So the constellations have stayed in the same place in relation to each other, but the signs associated with astrology have drifted to the west, and they no longer coincide with the constellations. If we go back to our random person born in the first two weeks of March; astrologically speaking he is a Taurus; astronomically speaking he is an Aries. The sun is actually in Virgo for people supposedly born under the sign of Libra, Gemini is now Taurus and so on. Yes, astrology is built on some pretty shaky, constantly changing ground.

Even more interesting is the fact that the Sun actually resides in the constellation Ophiuchus for a good piece of the year, yet there is no astrological sign for Ophiuchus. Yes, children, there should be a thirteenth astrological sun sign, Ophiuchus.

How did this great injustice happen, and what is an Ophiuchus?

When the astrological sun sign system was set up more than two thousand years ago, the sun’s path across the sky was divided into twelve equally spaced “signs,” each 30 degrees wide. The full 360 degrees around the sky divides up quite nicely into equal parts of 30 degrees. The stars however, aren’t quite so conveniently arranged. These ‘signs’ have never lined up very well with the actual constellations in the sky. For one thing, the constellations are all of various sizes and shapes. Virgo is the second largest constellation in the sky as measured in square degrees, yet Cancer, coming in at 31st largest, gets the same area according to astrology.

Worse yet, every astronomer and astrologer had his own idea of where the constellations began and ended, and even how many constellations there were. Everyone who drew a star atlas had a different version of the picture associated with the constellation and which stars belonged to which constellations. The constellation Libra was arbitrarily created by cutting off poor Scorpio’s claws to help round out the astrological need for twelve signs. Constellations aren’t real. People made them up, created great stories and legends associated with the characters, and passed them down through the ages as part of their culture.

Legends and ambiguity may be fine for astrologers and folklore, but scientists have more stringent specifications. Astronomers finally brought order to the confusion when the International Astronomical Union set the official constellation boundaries in 1930. Each constellation was published as a set of specifications that reads like a surveyor’s plot of irregular parcels of land. This redrawing of the boundaries added a constellation to the Zodiac.

The Zodiac, the constellations that lie on the plane of the ecliptic through which the sun passes in the course of a year, now has 13 constellations, not 12. This thirteenth ‘sun sign’ of the zodiac is Ophiuchus, the Serpent Bearer, and the sun is in front of its stars during the first half of December. As it turns out, most Sagittarians are really Ophiuchans.

Astrology is really a mess. It’s based on the superstitious belief that the apparent path of the Sun and planets against the background of stars, divided into constellations of fictitious beasts, monsters and legends, which no longer line up with the actual positions on those dates, and made up by ancient people who thought the earth was flat. It doesn’t have anything remotely to do with your personality or fate.

So, who is this Ophiuchus anyway? The Greeks knew him as Asclepius, the god of medicine. Asclepius was the son of Apollo and Coronis. Coronis was the goddess of Mexican beer. Not really, just kidding.

According to legend, Coronis was an unfaithful wife to Apollo and slept with a mortal, Ischys, while she was pregnant by Apollo. A crow brought Apollo this unwelcome news, but instead of rewarding the raven, which until then had been snow-white, he was cursed by Apollo and turned black and lost his voice. This crow or raven is also immortalized in the sky as the constellation Corvus.

Then, in a typical Greek god fit of rage and jealousy, Apollo shot Coronis with an arrow, but rather than see his unborn child perish with her, Apollo snatched the unborn child from his mother’s womb just as the flames of her funeral pyre engulfed her, and took the infant to Chiron, the wise centaur, also represented in the sky by the constellation Centaurus. The centaur raised Asclepius as his own, teaching him the arts of healing and hunting. Asclepius became so skilled in medicine that not only could he save lives; he could raise the dead.


Raising people from the dead is the line in the sand I draw between fiction and fact; astrology and astronomy. And that is why when people ask me what my “sign” is, I tell them ‘Caution; rough road ahead’ or STOP!

If you happen to be a proud Ophiuchan, your constellation has some things that actually exist in the sky, whose astronomical splendor you can observe throughout the late spring and summer. First of all, it contains seven Messier globular clusters- M9, M10, M12, M14, M19, M62 and M107- making Ophiuchus pretty much the king of globular clusters. Also, NGC 6240, the strange remnant of a merger between two smaller galaxies, resulting in a single larger galaxy, with two distinct nuclei and a highly disturbed structure. The high proper motion star and one of the closest stars to the Sun, Barnard’s Star can be found in Ophiuchus, as well as RS Ophiuchi, a recurrent nova thought to be teetering on the brink of becoming a Type 1A supernova.

It’s fun to learn the meaning and the legends behind all the astronomical names, made up by people thousands of years ago as they looked to the sky in amazement at celestial patterns and motions they didn’t understand. But it’s a lot more fun to observe the heavens through the eyes of a 21st century critically thinking human being, capable of understanding to a great extent, the origin, history and fate of our universe. The universe is beautiful, amazing and mysterious without the mumbo-jumbo.

You can read more about stars, stellar evolution, variable stars, and more, on my blog Simostronomy at

Until next time, so long.

End of podcast:

365 Days of Astronomy
The 365 Days of Astronomy Podcast is produced by the Astrosphere New Media Association. Audio post-production by Preston Gibson. Bandwidth donated by and wizzard media. Web design by Clockwork Active Media Systems. You may reproduce and distribute this audio for non-commercial purposes. Please consider supporting the podcast with a few dollars (or Euros!). Visit us on the web at or email us at Until tomorrow…goodbye.