Video: Global shift throws star signs out of whack

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updated 1/14/2011 2:00:22 PM ET 2011-01-14T19:00:22

If you look to your horoscope for a preview of your day, look again: You're probably following somebody else's supposed fate.

Thanks to Earth's wobble, astrological signs are, well, bunk. (Or even more bunk than you might expect.) Astrological signs are determined by the position of the sun relative to certain constellations on a person's day of birth. The problem is, the positions were determined more than 2,000 years ago. Nowadays, the stars have shifted in the night sky so much that horoscope signs are nearly a month off. [Read: Why Your Horoscope for 2011 Is All Wrong ]

"Astrology tells us that the sun is in one position, whereas astronomy tells us it's in another position," said Joe Rao, SPACE.com's skywatching columnist and a lecturer at New York's Hayden Planetarium.

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The shift is caused by precession, the wobble in the Earth's axis caused by the gravitational attraction of the moon to the Earth's equator. Precession popped into the spotlight this week after Minnesota Planetarium Society board member Parke Kunkle told the Minneapolis Star-Tribune about the gap between the astrological and the astronomical view. The story spread around the Internet quickly, but it's actually old news, Rao said.

Very old news.

"The earliest known astronomer to recognize and assess the movement of precession was Aristarchus of Samos, who lived around 280 B.C.," Rao told LiveScience.

The attention triggered by his interview with the newspaper has been "astounding." Kunkle, who teaches astronomy at Minneapolis Community and Technical College, told Livescience, He gave the interview at the request of the paper to discuss precession, and the science he described is centuries old, he said.

"Bombshell dropped?" Kunkle said. "Well, no, not really."

Here's what astronomers know: The Earth is like a wobbly top. As it rotates, its axis swings in a circle, pointing in different directions. As the Earth's position shifts, so does our perspective of the night sky.

For example, Rao said, we take the North Star, Polaris, for granted. It's the star most closely aligned with Earth's North Pole. But back when the pyramids were constructed, the star that aligned with the North Pole wasn't Polaris at all: It was a star in the constellation Draco called Thuban. In 12,000 years, Earth's North Star will be Vega, the brightest star in the constellation Lyra.

The complete rotation takes 26,000 years, Rao said.

"Everything in the sky is in flux," he said.

Even if the astrological signs were stable, there's no evidence the stars have anything to do with people's day-to-day existence. One 2006 study published in the journal Personality and Individual Differences used data from more than 15,000 people and found no relationship between date of birth and personality.

Despite the complete lack of scientific and observational evidence for astrology, 25 percent of Americans still believe in it, a recent Pew survey found. So here are the "real" dates of astrological signs, according to astronomers:

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  • Capricorn: 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.
  • Scorpio: Nov. 23-29.
  • Ophiuchus: Nov. 29-Dec. 17.
  • Sagittarius: Dec. 17-Jan. 20.

The list includes Ophiuchus, a formation the ancient Babylonians discarded because they wanted 12 star signs, not 13. That's yet another example of how astrologers cherry-pick and ignore astronomical observations, Rao said.

"It's crazy," Rao said. "Really, they have their own set of rules."

Nevertheless, maybe some good will come of the astrology-astronomy media blitz, Kunkle said.

"At the very least, I hope it makes people go out and actually look at the sky," Kunkle said. "That's the fun part."

You can follow LiveScience senior writer Stephanie Pappas on Twitter via @sipappas.

© 2012 LiveScience.com. All rights reserved.

Photos: Month in Space: January 2014

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  1. Southern stargazing

    Stars, galaxies and nebulas dot the skies over the European Southern Observatory's La Silla Paranal Observatory in Chile, in a picture released on Jan. 7. This image also shows three of the four movable units that feed light into the Very Large Telescope Interferometer, the world's most advanced optical instrument. Combining to form one larger telescope, they are greater than the sum of their parts: They reveal details that would otherwise be visible only through a telescope as large as the distance between them. (Y. Beletsky / ESO) Back to slideshow navigation
  2. A balloon's view

    Cameras captured the Grandville High School RoboDawgs' balloon floating through Earth's upper atmosphere during its ascent on Dec. 28, 2013. The Grandville RoboDawgs’ first winter balloon launch reached an estimated altitude of 130,000 feet, or about 25 miles, according to coaches Mike Evele and Doug Hepfer. It skyrocketed past the team’s previous 100,000-feet record set in June. The RoboDawgs started with just one robotics team in 1998, but they've grown to support more than 30 teams at public schools in Grandville, Mich. (Kyle Moroney / AP) Back to slideshow navigation
  3. Spacemen at work

    Russian cosmonauts Oleg Kotov, right, and Sergey Ryazanskiy perform maintenance on the International Space Station on Jan. 27. During the six-hour, eight-minute spacewalk, Kotov and Ryazanskiy completed the installation of a pair of high-fidelity cameras that experienced connectivity issues during a Dec. 27 spacewalk. The cosmonauts also retrieved scientific gear outside the station's Russian segment. (NASA) Back to slideshow navigation
  4. Special delivery

    The International Space Station's Canadian-built robotic arm moves toward Orbital Sciences Corp.'s Cygnus autonomous cargo craft as it approaches the station for a Jan. 12 delivery. The mountains below are the southwestern Alps. (NASA) Back to slideshow navigation
  5. Accidental art

    A piece of art? A time-lapse photo? A flickering light show? At first glance, this image looks nothing like the images we're used to seeing from the Hubble Space Telescope. But it's a genuine Hubble frame that was released on Jan. 27. Hubble's team suspects that the telescope's Fine Guidance System locked onto a bad guide star, potentially a double star or binary. This caused an error in the tracking system, resulting in a remarkable picture of brightly colored stellar streaks. The prominent red streaks are from stars in the globular cluster NGC 288. (NASA / ESA) Back to slideshow navigation
  6. Supersonic test flight

    A camera looking back over Virgin Galactic's SpaceShipTwo's fuselage shows the rocket burn with a Mojave Desert vista in the background during a test flight of the rocket plane on Jan. 10. Cameras were mounted on the exterior of SpaceShipTwo as well as its carrier airplane, WhiteKnightTwo, to monitor the rocket engine's performance. The test was aimed at setting the stage for honest-to-goodness flights into outer space later this year, and eventual commercial space tours.

    More about SpaceShipTwo on PhotoBlog (Virgin Galactic) Back to slideshow navigation
  7. Red lagoon

    The VLT Survey Telescope at the European Southern Observatory's Paranal Observatory in Chile captured this richly detailed new image of the Lagoon Nebula, released on Jan. 22. This giant cloud of gas and dust is creating intensely bright young stars, and is home to young stellar clusters. This image is a tiny part of just one of 11 public surveys of the sky now in progress using ESO telescopes. (ESO/VPHAS team) Back to slideshow navigation
  8. Fire on the mountain

    This image provided by NASA shows a satellite view of smoke from the Colby Fire, taken by the Multi-angle Imaging SpectroRadiometer aboard NASA's Terra spacecraft as it passed over Southern California on Jan. 16. The fire burned more than 1,863 acres and forced the evacuation of 3,700 people. (NASA via AP) Back to slideshow navigation
  9. Where stars are born

    An image captured by NASA's Spitzer Space Telescope shows the Orion Nebula, an immense stellar nursery some 1,500 light-years away. This false-color infrared view, released on Jan. 15, spans about 40 light-years across the region. The brightest portion of the nebula is centered on Orion's young, massive, hot stars, known as the Trapezium Cluster. But Spitzer also can detect stars still in the process of formation, seen here in red hues. (NASA / JPL-Caltech) Back to slideshow navigation
  10. Cygnus takes flight

    Orbital Sciences Corp.'s Antares rocket rises from NASA's Wallops Flight Facility on Wallops Island, Va, on Jan. 9. The rocket sent Orbital's Cygnus cargo capsule on its first official resupply mission to the International Space Station. (Chris Perry / NASA) Back to slideshow navigation
  11. A long, long time ago...

    This long-exposure picture from the Hubble Space Telescope, released Jan. 8, is the deepest image ever made of any cluster of galaxies. The cluster known as Abell 2744 appears in the foreground. It contains several hundred galaxies as they looked 3.5 billion years ago. Abell 2744 acts as a gravitational lens to warp space, brightening and magnifying images of nearly 3,000 distant background galaxies. The more distant galaxies appear as they did more than 12 billion years ago, not long after the Big Bang. (NASA / NASA via AFP - Getty Images) Back to slideshow navigation
  12. Frosty halo

    Sun dogs are bright spots that appear in the sky around the sun when light is refracted through ice crystals in the atmosphere. These sun dogs appeared on Jan. 5 amid brutally cold temperatures along Highway 83, north of Bismarck, N.D. The temperature was about 22 degrees below zero Fahrenheit, with a 50-below-zero wind chill.

    Slideshow: The Year in Space (Brian Peterson / The Bismarck Tribune via AP) Back to slideshow navigation
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