How accurate is astrology?

Do you believe in astrology?

Almost every semester I have a student or two asking about astrology.  They know it’s different from astronomy, the college course I’ve been teaching the last ten years.

I imagine one could wonder “What kind of differences are there between astrology and astronomy? ”   “The words are so similar; and don’t both words begin with the same five letters?  “Aren’t both concerned with the positions of the Sun, planets and stars?”

They do seem similar, don’t they?  On a superficial level, it’s true.  But a superficial level of understanding of science in general and astronomy in particular, is what many people have.

This semester I arranged a little demonstration that might show the differences between astrology and astronomy.

I told the assembled class of 100 students that I wanted them to see the way science works.  I said a few words about the scientific method taught in 7th grade, and a little about the process of science;

I referred the model you can find at “The real process of science” linked here.

 Basically:   Question.


                       Collect data.


                       Impose a structure on the data.


I’m sure you remember.  The actual process is much more complicated.  Students were told the activity was about the process of science,  I wanted them to see an abbreviated example of the process.

IMG_2688I handed out copies of a horoscope column from the previous day.  I had removed all references to the sun signs and rearranged the 12 paragraphs, the astrological  “advice” for the day.

I directed the students to do their best and really try to read all 12 short paragraphs and pick the one that best matches their day “yesterday.”

We talked a bit about what percent of success in our experiment would give them pause.  How many correct matches would have to occur for them to wonder if astrology works?


I arbitrarily gave them four choices and I asked them to indicated which choice is closest to their minimum threshold.

Thus is how they voted:


What is the minimum threshold for astrology to become interestingly accurate for you?

Min accuracy

Number of students









I explained that pure random choice, would get somewhere around 8% correct.  If everyone just closed their eyes and randomly pointed a finger at one of the 12 choices, we’d get around 8% correct.

My sign.

After putting their name and birthdate on the page, I directed them to find the astrological advice that seems to be the most appropriate for their day yesterday.  “I really need for you to try, really try to do your best.”  And they did seem to try.

They traded papers with a neighbor and I displayed the answer key on the slides.  I asked everyone to write a note about the correct match for each birthday.

Then we asked the students to tell us who had a paper with a correct match.

Report from student

How many

Accurate match


Inaccurate match


Student generated data

Evidence-based conclusion statement:

  Astrology is apparently as accurate as random chance.  With twelve paragraphs, and the students trying their best, 8 students out of 100 were able to accurately choose their astrological advice in our experiment.  That is the same as random chance, and indicates astrology is for entertainment purposes only.  While we only had 100 students responding, the 8% rate was right on point and seems to make up for any deficiency else where.  I also depended on student really trying to pick the right match.  It’s possible some were anxious to leave because we were approaching dismissal time.  The experiment makes me wonder how the process of science also uses the imagination of the scientists.

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