The wobble in our stars

The world of astrology (yes, I used that word) was set on its collective ear last week when astronomer Parke Kundle of the Minnesota Planetarium Society was quoted in the Minneapolis-St. Paul Monitor as adding a 13th constellation to the zodiac and proposing a change in the dates for when the sun was in any particular zodiacal constellation.

Astrology is guided by what sign, or constellation, the sun is in front of on a given date. What Mr. Kunkle did was simply state a truth that astronomers have known for years, at present the sun is not in front of the sign the astrologers day it is.

Because of a process called precession the particular constellation the Sun is in front of has shifted at least one month from what it was 3,000 years ago when the zodiacal constellations were set. It has gone one month to the right, from Capricornus into Sagittarius.

Precession is the result of the gravitational pull of the sun and moon which gives Earth's axis a slight wobble. That means the direction it points does not stay the same.

As I have said before, it is like a child's top when it begins to slow down its axis wobbles. Such is Earth's axis wobbling.

Now the axis points almost directly at Polaris, the North Star. Several thousand years ago the axis pointed to a star in the constellation Draco named Thuban making it the pole star. In another 12,000 years the pole star will be Vega in Lyra.

The total time Earth's axis takes to proscribe a full circle is about 26,000 years.

The predictions Astrologers make are based on the assumption that the sun spends a full month in front of each constellation but such is not the case. For some constellations the sun only skims through its borders. For others it goes straight through the middle.

In fact, one constellation which the sun skims through in just 19 days is totally left out of astrological calculations all together. The constellation Ophiuchus (pronounced Ooh-FEE-you-kus), the Serpent Bearer, is above Scorpius and Sagittarius but a little bit of its boundary extends down between them placing it within the range of the zodiac.

As for the stars having any effect on our lives or personalities I defer to what William Shakespeare had one the characters in his play Julius Caesar say. Cassius says to Brutus, "The fault, dear Brutus, is not in our stars, but in ourselves that we are underlings."

Besides, if the dates for zodiacal consideration do change I go from being a lion to being a crab. Well, at least my wife would agree with that.

SKY WATCH: Full moon yesterday so there won't be much observing, at least for a couple of days. However there are a few things in the morning sky worth taking a look at. On Thursday and Friday about an hour before sunrise watch as the moon plays tag with Leo's brightest star Regulus. Venus is blazing brightly in the southeastern morning sky. On Monday and Tuesday, Jan. 24 and 25 the moon will play tag with Saturn. Now is a good time to use that telescope you got for Christmas to check out Saturn. The bright star above the moon on Tuesday is Spica, the brightest star in Virgo.

NEXT WEEK: More astronomical blathering.