Signs of the zodiac may have changed, but they're still all bull

In the recent kerfuffle about the "new" zodiac sign and how your astrological sign has changed, we seem to have lost sight of the fact that astrology is not science -- it's a scam. So let's talk about how we see the sun, moon planets and stars from our earthbound location and what it means for astrology.

Astrology asks us to believe that the positions of the sun, moon and planets have a significant effect on each of us -- and that the effect depends not on the current location of those orbs, relative to us, but on their location at the instant of our birth.

But there's a problem: The sun would have been in Gemini in mid-June 4,000 years ago, but it is in Taurus in mid-June today. Even worse -- many "Sagittarreans" have learned that the sun was, in fact, in a constellation known as Ophiuchus when they were born. Why has this happened, and at does it all mean?

The position of the sun relative to the background stars is affected by precession. Although many people believe that one Earth year is the time it takes for us to orbit the sun once (i.e., travel through exactly 360 degrees), that is not true. We set our calendar by the time between spring equinoxes. Because the Earth's rotational axis itself rotates very, very slowly - the sidereal year (360 degrees) and the tropical year (the time between vernal equinoxes) are about 20 minutes different. Not much difference, but over a few millennia the effect starts to show up in the stars' location at different times of year.

Astrologers will tell you that it doesn't matter, because they do "tropical astrology." What is that, exactly? When we measure or calculate the positions of the planets, the sun and the moon, we do it with respect to the stars -- not the equinox. "Tropical astrologer" is a scam to keep you coming back for more.

Now let's tackle Ophiuchus. One of the issues we deal with in astronomy the science (as opposed to astrology, which is not science) is that humans have been stargazing for an awfully long time. Consequently some of our systems of measurement and terminology have historical roots. And so it is with Ophiuchus.

Man has always had stories to aid in remembering the order and positions of the stars. When the zodiac was originally defined as the constellations through which the sun, moon and planets would pass, there weren't any official boundaries. Then, in 1930, the International Astronomical Union (IAU) decided we needed to define locations in the sky by their constellations, and defined constellation boundaries.

Lo and behold, the path of the sun passes through a 13th sign: Ophiuchus. It's not that we shifted, or that the stars shifted; we just finally defined the edges of constellations, just as in 2006 we finally defined what it means to be a planet, leading to the official demotion of Pluto.

And here's another problem for astrology. In the ancient world, when we thought the Earth was the center of everything, we knew of only five other planets, plus the sun and the moon. Uranus wasn't discovered until 1781; Neptune, 1846, and Pluto, 1930. So if you happen to be Aquarian, Piscean or Scorpion, your sign didn't have a ruler until relatively recently (astronomically speaking). And if your sign is Scorpio -- you have a dwarf planet for a ruler.

So what does it all mean? It means that astrology is and always has been complete and utter nonsense.

Enjoy reading your horoscope. Remember it's made up and get on with your life.

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Angela Speck, Ph.D., an associate professor of physics and astronomy at the University of Missouri, is a source in MPR's Public Insight Network.

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