Thursday, January 13, 2011


Glanced at Yahoo! News today and saw this article:

Earth’s ‘wobble’ means your zodiac sign may be wrong

The Yahoo! News article starts out stating: "A Minnesota astronomer confirms what many have suspected: Your horoscope is quite possibly wrong."  A phrase comes to mind - "No shit, Sherlock" since astrology is a bunch of hokum but their point, however, was that the wobble of the Earth's axis means your supposed horoscope sign doesn't correspond to the positions of the astronomical constellations anymore.

Let's throw a little science into this discussion (something news articles never do since they assume everyone's a flaming idiot).  What does it mean to say your sign is Aries anyway?  Well, it started with the ancient Mesopotamian cultures around 3,000 BC who observed the sky each night (easy to do without light pollution and TV in a clear-sky desert climate) and noticed that the Sun, Moon, and planets follow a path through the sky which today we call the ecliptic.  It's the plane of the solar system (they assumed everything orbited the Earth back then while today we know it's the plane in which everything orbits the Sun - except, of course, for our moon).

They then developed 12 constellations roughly evenly spaced on the path of the ecliptic (I say "developed" because there's nothing special about the constellations, they're just random patterns of stars we choose to see as related).  From the perspective of us here on Earth, as the year progresses (as we orbit the Sun) we see the Sun passing through each of the 12 constellations each month.  That's why your horoscope sign is called your Sun sign.  Supposedly, if you're an Aries, the Sun was in the constellation of Aries - in other words, from the Earth's surface, the Sun is in line with the stars which make up the constellation of Aries.

Gravitational forces between the Earth, Sun, and Moon cause the Earth's axis to wobble like a slowing top.  This induces an approximately 26,000 year cycle called the precession.  Since the time the ancient cultures of Mesopotamia developed the ideas of astrology thousands of years ago until today, the dates that the Sun enters each of the zodiacal constellations has shifted.

I was born on April 17 and therefore an Aries according to traditional astrology (March 20 or vernal equinox date to April 20).  But if I use a planetarium program like Stellarium, I see that on April 17, 2011 the Sun is squarely in the constellation of Pisces.

Here's an easy to read explanation if you want a bit more detail (What's your sign? The science behind the zodiac).

As you trace this article back from Yahoo! News (credited to Liz Goodwin), to Time NewsFeed (credited to Megan Friedman), to the Minneapolis Star-Tribune (credited to Bill Ward), you actually see that the original story wasn't that bad.  It was a Minnesota Planetarium Society board member Parke Kunkle talking to a reporter about astrology on what was likely a slow news day.  No problem.  By the time the story went through Time and got to Yahoo! News, it was treated like a new discovery.  The Time NewsFeed article breathlessly claims:

"The field of astrology, which is concerned with horoscopes and the like, felt a major disruption from astronomers, who are concerned with actual stars and planets. The astronomers from the Minnesota Planetarium Society found that because of the moon's gravitational pull on Earth, the alignment of the stars was pushed by about a month."

Problem is, astronomers have known about precession since the time of the ancient Greeks - Hipparchus knew about it around 140 BC!  This is not anything new and certainly no "finding" of the Minnesota Planetarium Society (nor would they claim that!).  It's just sloppy journalism.

So why don't astronomers believe in astrology?  Not because of the precession (although it is good evidence that astrology is bullshit).  Simply because it makes absolutely no sense given our modern knowledge about the universe.  Let's look at the constellation of Aries, the ram.

From left to right, the stars that make up the main part of this constellation are Bharani or 41-Arietis, Hamal or a-Arietis, Sheratan or b-Arietis, and Mesarthim or g1-Arietis.  They are, respectively, about 160, 66, 60, and 204 light years away from Earth.  They are not related to each other in any way.  How the hell could those disparate stars affect us at the moment of our birth just because they're in the same direction as our Sun (and millions of times further away)?  And why our birth date - what if you were a preemie?  Isn't the date of conception more significant?  It just makes no sense.

According to a November-December, 2009 Harris poll, 26% of U.S. adults surveyed believe in astrology (not the 31% incorrectly reported in the Minneapolis Star-Tribute article!).  Not surprising since a 1999 Gallup poll showed that 18% of Americans believe the Sun orbits the Earth (science settled that one about 500 years ago).  A certain percentage of people are completely ignorate of modern science, it's that simple.

It does annoy me, however, that newspapers carry astrology columns every day but rarely write anything about real science (and, when they do, it's usually bullshit like the Yahoo! News article that started me off on this topic today).


  1. Thank you very much for this article. I've been searching the web for a rational point of view on this and have finally found one. I never believed that astrology was the way things were necessarily, and I've known the alignment of the stars has been off for awhile, so naturally I was curious to read up about how this became news. I've always followed what I thought was my sign, and in many cases my horoscopes have been accurate - but in many cases I have not. Reading up on the description of my "new" sign, Scorpio, I realized the traits fit me almost as well as those of Sagittarius, my "old" sign. I started to wonder if the position of the stars actually meant anything, or if it was just our minds tricking us into believing something completely false, as modern psychology shows they are so apt to do.

  2. Hello,

    I found your recent 'Duh' blog while surfing the web in an effort to discover why the recent zodiac story is being treated by the media as if the Minnesota Planetarium just made a new discovery. I've known about the effects of precession since I became interested in astronomy as a teenager, which was a long time ago. When I saw the zodiac story on television today my first thought was; Why are they talking about this like it's news?
    I think you've done a good job of explaining how precession works and also how stories like this get inflated by the media. With your permission, I will forward your 'Duh' blog to some other media websites that need to be enlightened on the subject.


    BTW- I'm partial to your birth date. It happens to mine too. I guess we're both Pisces now. ;)

  3. Considering there is countless if not an infinite supply of stars and constellations, couldn't one argue that no matter how many ' zodiac signs ' there are it would work regardless. Just because one group of ' astronomers 'decided to pick 12 groups of stars equally spaced a part does it make it right? What if this original group of ' astronomers ' decided to choose 6, 15, 20, 30 or whatever number you can fathom, evenly spaced apart throughout the year that all fit in the celestial pattern. Wouldn't they technically still be accurate?