Here’s a Google Trends graph showing searches for “Ophiuchus” over the last 30 days. The spike comes after a Minnesota astronomy instructor, Parke Kunkle, mentioned in an interview that the sun glides through the constellations of the zodiac on a different schedule than it did a few thousand years ago, and therefore the dates for the zodiacal signs used in astrology no longer match up with the sun’s position. To add to the fun, he mentioned that, in addition to the famous twelve, the sun also passes through Ophiuchus, the serpent bearer. Chaos ensued.
As Kunkle knew, the shift he spoke of has been known for over 2,000 years. It is due to the Precession of the Equinoxes, the same wobble that means Polaris has not always been and will not always be our North Star. Precession is covered in most Astronomy 101 courses, including ours. Why this old news went viral would be an interesting question to explore some time.
Astrologers were quick to point out that they use a “Tropical Zodiac” anyway. In it the signs are merely seasonal markers, now independent of the constellations from which they originally drew their names. Not that I endorse the practice of astrology, but fair enough. As someone interested in sundials, I have seen the zodiacal signs used as seasonal markers in just this way.
Case closed? Hardly! It’s a great excuse to demonstrate the Precession of the Equinoxes and point out Ophiuchus at the 2011 New Year show this Sunday and Monday. (See the calendar on the planetarium site for more info.)