A change in zodiac signs is written in the stars — or is it?
According to the National Science Foundation, 15 percent of Americans read their horoscope on a daily basis to chart their personality traits and to foresee future events as predicted by star positions.
In an interview last month with the Minneapolis Star Tribune, however, astronomer Parke Kunkle claimed that scientists have known for centuries that there is actually a 13th zodiac sign called Ophiuchus.
The wobble of the Earth's orbit, Kunkle said, has caused the zodiac signs to shift. But when a series of astrologers rejected the validity of the new sign, the story went viral, setting off panic among those who rely on astrological charts to "predict" their futures.
Kunkle, an astronomy instructor at Minneapolis Community and Techincal College, said in the interview that knowledge of Ophiuchus' existence is hardly a recent development.
Joyce Levine, an astrologer in Cambridge, agreed.
"This is nothing new," Levine told the Daily. "The earth is an ellipsoid, and that creates a wobble in the orbit, so as the earth revolves around the sun each year, it doesn't hit the same place when it gets back. This is called the ‘precession of the equinoxes.'"
Astrologers have long been acutely aware of this phenomenon, but consider it irrelevant to tropical astrology, which is used in the Western world, according to Levine.
"Basically, we know about the precession of the equinoxes," she said. "It's just not based on the system that we're using. That's the bottom line."
The signs in tropical astrology correspond to the beginnings of seasons, with two "intermittent" signs between the start of a new seasonal solstice or equinox.
The other school of thought in astrology, called sidereal or vedic astrology, is used predominantly in the non−Western world and is based on the position of the sun relative to the zodiac constellations (Leo, Virgo, Gemini, etc.)
Sidereal astrology marks the start of each zodiac sign by the time of year when the sun is in the given zodiac constellation, according to Levine. For example, people born during the part of the year when the sun is aligned with the constellation Sagittarius would have Sagittarius as their zodiac sign.
The 13th sign, Ophiuchus, Levine said, was used by the Babylonians, but later discarded for an even 12 zodiac signs.
To make a long story short, horoscope devotees need not panic — their entire lives have not, in fact, been based on a lie. Precession has no bearing on zodiac signs in tropical astrology.
"Ptolemy said that [precession] will slowly change the way we see the constellations, and therefore the system ought to be corrected for that," Professor of Physics and Astronomy Kenneth Lang said. "The version that corrects for that is tropical and the one that does not is sidereal."
Assistant Professor of Physics and Astronomy Anna Sajina points out that most casual zodiac devotees do not understand the distinction between tropical and sidereal astrology.
"Even though [tropical astrology] might be what professional astrologers look at, the vast majority of people base their horoscope on the month they were born in and what sun sign is traditionally attached to that month," she said. "People still think of it as what was the sign that the sun was in when they were born, and that's not true."
As Kunkle said, the sun's relative position to different constellations changes slightly each year, causing the precession of the equinoxes referred to by Levine.
Lang elaborated upon the concept.
"What precession is … is that the earth is not exactly spherical; it's more like an egg, and the moon and the planets both pull on that aspherical shape and cause the earth to wobble in space," he said. "This causes the rotation of the earth to wobble like a top."
Sajina attributed this phenomenon to the significance of Earth's rotation on its axis. Since the earth rotates on an axis and around the sun, the axis is oriented 23.5 degrees off north, she said, and slowly traces a circle around north.
"To complete the circle takes 26,000 years. Because of this, the sun signs change over time," Sajina said. "Since it's only been about 4,000 years since the zodiac was invented, we've only gone one−tenth of the way around the circle. It's going to take 22,000 years to get back to the original configuration."
Minneapolis Star Tribune staff writer Bill Ward, who interviewed Kunkle and initiated the media blitz, noted that just because these facts were available doesn't mean that the ideas were disseminated.
"Most of our readers didn't know about [the distinction between tropical and sidereal astrology]," Ward said. "It's in the public domain, like old books or old music are public domain, but that doesn't mean that everybody takes advantage of that."
