My horoscope today on astro.com says “this is a good day for a short recreational trip to indulge your desire for beautiful surroundings,” “you should be able to negotiate in business to your advantage,” and “anything that you buy today should prove to be a worthwhile investment.”

Now, let’s think about that. The current world population is about 6.5 billion, and a twelfth of us are Pisces. Can 540 million people all negotiate favorable business deals on the same day?

Astrologers would say no, those general predictions are worthless, what really counts is a personal reading. Okay, then astrologers should be able to match a person’s birth data with a personalized questionnaire, right? Well, no: A 1994 experiment showed they might as well flip coins.

Even if you accept astrology’s tenets, its reasoning doesn’t make sense. For one thing, the stars are drifting. Due to the precession of Earth’s axis, the stars have moved by 24 degrees during the last 2,000 years. Following the old charts, astrologers are now placing planets in the wrong signs.

For another, that 2,000-year starting point is arbitrary. The heavens change all the time. Four thousand years ago Taurus was the constellation of the vernal equinox. Six thousand years ago it was Gemini.

Anyway, if you’re into this stuff, the rather creepy Horoscopes of Our Time lists precise birth dates and times of various famous people, so you can practice.