Catch a falling star...

9th September 2005 at 01:00
Chris Holt predicts that some lessons in debunking astrology will give students the skills they need to spot fake science

During the most scientifically advanced period of human history, belief in magic and superstition is on the increase. Irrational beliefs are an obstacle to creativity and inhibit the intellectual development of our pupils. We scientists and science teachers should do all we can to persuade students to be more critical and questioning, so that they can recognise fake science when they see it.

Astrology is one irrational belief which is widespread and particularly pernicious. Pernicious because it encourages us to avoid responsibility for what we do and what happens in our lives. According to astrology, we do not have complete free will but instead are controlled by movements of the Sun, the Moon, the planets and the stars. Sadly, according to polls, the majority of people in Britain now think that astrology is valid, and the Association of Professional Astrologers claims that 80 per cent of Britons regularly read star columns in newspapers.

With some classroom activities and general discussion you should be able to convince your students that astrology is nonsense. In the process you can introduce a little history, some physics, the statistics of small numbers and an example of how to weigh evidence and test scientific theories. These activities can be adapted to all key stages.

Testing professions

Astrologers believe that positions of the Sun, Moon and planets against the star pattern at the time of your birth influence your personality and your destiny - for instance, that your star sign will influence your choice of profession. Why not test this with British Prime Ministers? There have been 51 Prime Ministers so far; their dates of birth (and other biographical details) can be found on the Downing Street website

These birth dates can be translated into star signs using newspaper star columns to get the dates. If astrology's assumptions are correct, you would expect the star signs of British Prime Ministers to cluster, with some star signs not represented at all (point out that Virgos are defined astrologically as weak leaders).

However, with only 51 data points, the distribution is a bit lumpy and if your students are unfamiliar with the statistics of small numbers they may think the lumps and bumps are significant. In which case you might want to go to a larger sample size and choose other occupations: sportspeople who win medals in the Olympics might be a popular choice.

Personality profiles

Another activity might seem a bit mean, but it is a trick similar to that which the psychologist Bertram Forer played on his students. Ask each of your students for their date of birth and then say that you are going to prepare a personality profile based on astrology.

Then return the following day and hand out the following "personality profile" to all of them: "You have a need for other people to like you and admire you, and yet you tend to be critical of yourself. While you have some personality weaknesses you are generally able to compensate for them.

You have considerable unused capacity that you have not turned to your advantage. Disciplined and self-controlled on the outside, you tend to be worrisome and insecure on the inside. At times you have serious doubts as to whether you have made the right decision or done the right thing. You prefer a certain amount of change and variety and become dissatisfied when hemmed in by restrictions and limitations. At times you are extroverted, affable and sociable, while at other times you are introverted, wary and reserved."

It's important that your students do not know they have all been given the same profile. Now ask them to score the accuracy of the profile on a scale of 0-5. When Forer did this, the average score of his students was 4.26. In truth, the description in the profile, compiled from newspaper astrology columns, is so vague and general that most people would agree that it describes them.

Comparing columns

A quick comparison of astrological columns in different newspapers on any one day shows virtually no agreement. Demonstrate this to your class in several ways. Maybe cut out the predictions but omit the star sign, then get the class to see if they can match up the predictions from the different astrologers. Or you could use yourself in the experiment: ask them to read out your own predictions for the day from the various astrologers and let them discuss the differences.

Looking at history

If such practical activities do not convince, you could point out that all the star signs given by astrologers are wrong. Your star sign is the constellation of stars which formed the backdrop to the Sun when you were born.

But the charts which astrologers use were drawn up 2,000 years ago, and the stars today are in different positions in the sky. The Earth wobbles very slowly on its axis (called precession), and the constellations move very slowly westwards, making a complete circuit in 26,000 years.

Over the past 2,000 years, the constellations have shifted back about one month, or about one star sign. So for almost everyone the correct sign is the one before the one they think it is.

As Richard Dawkins wrote: "My birthday (March 26) is listed in the papers as Aries but this is the Sun sign which somebody with my birthday would have had when Ptolemy codified all that stuff. Because of the precessional shift of approximately one zodiacal sign over the AD era, my Sun sign is in fact (if you can call it a fact) Pisces. If astrologers were doing something that had any connection with reality, this should make a difference. Since they aren't, it doesn't. Scorpio could go retrograde up Uranus and it wouldn't make any difference!"

Dr Chris Holt is a physicist and science writer based in Bedford E-mail:

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