By Frank D. Roylance, Baltimore Sun, First published Dec. 31, 2004

    Let's get one thing straight. I don't believe in astrology. But the daily horoscopes seem harmless enough back there with the funny pages, offering sensible, all-purpose advice.

    For example, The Sun's syndicated astrologer recently urged those born under Pisces to "back up computer files, and make sure your cell phone battery is charged." No argument there.That said, I confess that I can't wait until the next time somebody asks my astrological "sign." That's because I've been spending a lot of time with a computer program for backyard stargazers called Starry Night, published by Imaginova. It's a powerful tool for anyone curious about the night sky - like having Carl Sagan's ghost beside you on a magic-carpet tour of the night sky, and of all time and space. 

    I've discovered something deep inside this fascinating software that should kick the astrological legs out from under millions of believers. Although it probably won't.

    First, those dates you see in the newspaper, bracketing each of the 12 astrological signs? They're all wrong. And, because of something called the "precession of the equinoxes," they've been getting more and more out-of-whack since about 600 BC, when the astrological system was concocted.

    Second, because the dates are all wrong, almost nobody living today was actually born under the sign they think they were. Which means they've been reading - and taking - the wrong advice all their lives. No wonder the world is a mess!

    Third, and this is the most delicious part, those of us born between Nov. 30 and Dec. 17 aren't Sagittarians, as we have always believed. We were born with the sun in the constellation - get this - Ophiuchus.

    That's right: Ophiuchus, the serpent-bearer. It's pronounced Offy-YUK-us, and I had never heard of him either. No syndicated astrologer has ever offered a lick of advice to any of us Ophiuchans. But Starry Night displays his constellation big and bold, with his foot stuck right there between Scorpio and Sagittarius.

    What does it mean to say the sun is "in" a constellation? Well, remember that the sun is always perched in the sky against a backdrop of stars and constellations. We can't see the stars in the daytime (except briefly during a solar eclipse) because the sun's too bright.

    But we know the constellations are there. We can even see them in our night sky six months later, when the Earth has moved to the opposite side of the solar system.

    Think of the setup as a circular room with 12 portraits hanging on the wall. Each painting represents a constellation of stars. The sun is at the center of the room. As we (Earth) orbit around it, the sun appears to move in the opposite direction relative to the portraits in the background. Over one year, the sun seems to move through the full circle of paintings - all 12 constellations of the zodiac.

    Now I always believed I was born with the sun in Sagittarius (the guy with the bow and arrow). But it turns out, according to Starry Night, that nobody born on Dec. 10 has been a Sagittarian since 1582.

    When I set Starry Night's controls for my birth date, Dec. 10, and run the years backward, the computer puts all the heavens in motion. I can watch the sun move slowly eastward each Dec. 10 until 1582, when it finally pops back into Sagittarius - where it had been since at least 600 BC.

    Likewise, when I run the years forward from Dec. 10, 2004, the sun "precesses" - creeps slowly westward on the screen each Dec. 10 until the year 2770 or so, when it finally crosses from Ophiuchus into Scorpio (the scorpion).

    Who knew? Have astrologers been keeping this secret for 2,000 years?

    Not exactly. They're well aware of precession. And they're rolling with it.

    "When empirical data begins to disagree with a belief system, we reach a moment ... where you're either going to go with the data or with what you believe," said Holiday Mathis, who writes The Sun's astrology feature.

    Whether the western astrological zodiac matches up with the stars or not "is a moot point," she said. "The archetypes are only as meaningful as we attribute meaning to them. If they do not resonate inside of a person, then astrology is not for that person."

    The western astrologers' zodiac starts in whatever constellation the sun happens to be in on the vernal equinox - the first day of spring. They simply call it Aries (the ram), and apply all of Aries' relevant influences to their recommendations - regardless of what constellation the sun is really in. But more on that in a minute.

    According to Starry Night's "SkyGuide," the eminently readable text that serves as the user's guide and companion, the ancient astronomers who first formalized western astrology hadn't yet discovered "precession."

    They only saw that as a year went by, the sun moved along a celestial trail called the "ecliptic," slipping through a series of 12 constellations. Back then, the sun began its year at the vernal equinox when the sun really was in the constellation Aries. It spent about a month in each subsequent "house" before returning to Aries the following spring.

    Starry Night puts the sun in motion for you, and you can watch it glide through the year, from Sagittarius to Capricorn to Aquarius and so on, all the way around the sky. The ancients believed that our lives are influenced by whichever constellation the sun was traversing at the time we were born.

    Which scientists dismiss as poppycock, of course.

    "It's disturbing that people may be basing life decisions on something that ridiculous," said Dan Caton, a professor of astronomy at Appalachian State University in Boone, N.C., who has written columns in the Charlotte Observer debunking newspaper astrologists.

    There's no basis in science for a connection between the position of the stars and planets and the course of human lives, he said. And repeated statistical studies have found no evidence for such a connection.

    If the stars did influence our lives, he agreed, precession should become a concern - yet astrologers ignore it. But he insisted that "precession doesn't even matter. It's a third-order effect on a mechanism that's not there."

    It was the Greek astronomer Hipparchus who figured out in 134 BC that the astrologers' celestial frame of reference was moving. The spinning Earth wobbles slowly around its axis, like a slowing toy top, because of the gravitational tug of the moon. That wobble rotates in a 25,800-year cycle that gradually pushes the vernal equinox westward around the sky, throwing off all the zodiac's original dates.

    Since 600 BC, it has moved about 36 degrees, or one-tenth of the way around the zodiac. That's almost a whole month. It's like taking all the Beltway exit signs and moving each one to the next ramp.

    So, while newspaper astrologers still insist that anyone born on June 30 is a Cancer (the crab), those people were actually born with the sun in the constellation Gemini (the twins). The "real" Gemini now goes from June 20 to July 20. Then the real Cancer starts and lasts until Aug. 9.

    Precession also allowed the late-autumn sun to slip into all-new constellation territory, which is how Ophiuchus barged into the lineup between Scorpio and Sagittarius.

    It gets even squirrelier. The astrologers divided the sun's path along the ecliptic into 12 even segments - one per constellation. But constellations aren't all the same size, and it takes the sun longer to cross some than others.

    For example, it takes the sun from Sept. 16 until Oct. 30 to make its way across Virgo - that's 45 days. But it dashes through Scorpio in just a week, from Nov. 23 until Nov. 29.

    Now, if you believe that the positions of stars and planets influence your life, wouldn't it be important to know which constellation the sun was really in on your birthday, or any other day?

    Turns out it's not.

    Astrologers such as Mathis say they use the "tropical zodiac," which means they start their celestial year from the vernal equinox and call it Aries, no matter where the sun really is among the constellations.

    From there, they simply measure out each subsequent "sign" in 12 segments of 30 degrees each. The actual positions of the stars and constellations don't matter anymore. Their names are used as a matter of convenience and, as Mathis says, "mythology and storytelling."

    If nothing else, this little lesson demonstrates that there's a vast universe of both stars and ideas out there, with all kinds of surprises.

    For information on Starry Night, visit www.starrynight.com.