Unit 8 : Calendar System : Ancient Astronomy : Babylonian Astronomy and the Origin of Astrology : Unit Questionnaire

Unit 1: How to Point to a Star
Unit 2: Where on Earth Are You?
Unit 3: Earth's Rotation and the Sun's Apparent Motion
Unit 4: Yearly Changes in the Sky
Unit 5: Seasons and Climate
Unit 6: Sundials
Unit 7: Navigation
Unit 8: Ancient Astronomy
Unit 9: Constellations

Babylonian Astronomy
and the Origin of Astrology

With agriculture came the need for measuring and recording land ownership.  This commerce led to developments in writing, arithmetic, and geometry.  These developments were applied to astronomy, and made it possible to begin predicting where, for example, the planets would appear in the sky.

The Babylonians (who lived in the area that is now Iraq) gave us our 360 degree circle with 60 minutes in a degree and 60 seconds in a minute.  They liked base 60 arithmetic because 60 has many even factors.  The Babylonians kept careful records of the motions of the seven wanderers in the sky -- the five planets scene by the naked eye, plus the sun and moon.   They believed that the arrangements of the planets in the sky carried warnings about major disasters and historical events, and so they were very interested in recording and predicting these motions.

Astrology is the interpretation of motions and positions of celestial objects in an attempt to predict events on Earth.  This was a very natural extension from the great success of keeping track of the sun's apparent motions to predict the seasons.  After all, if the sun's apparent motion can tell you whether it is the cold season or the hot one, the rainy season or the dry one, why shouldn't those other lights in the sky be trying to tell you something too?  Ancient astronomers/astrologers (in those days these were the same, although today they are very different) did not believe that the planets were worlds orbiting the sun.  Most likely they believed the myths that they recorded, which indicated that these lights in the sky were gods who were frolicking in the sky and perhaps looking out for people on Earth.  So it made sense to try to interpret their motions as warnings of big events to come.

Astrology gradually developed to the form that it takes today.  Originally, it was used only to predict major events such as plague, earthquake, flood, famine, and war.  But individual kings and rulers, for example, usually started wars.  Astrology was then naturally extended to try to predict what would happen to kings and what kind of kings they would be.  Eventually, the Greeks, who invented political democracy, extended the ideas of astrology to include the personalities and fates of more ordinary citizens, and it is this form that survives today.

Our present understanding of the solar system and of the planets is not consistent with the idea that we can learn about our futures and personalities from the arrangement of the planets.  We now know that the planets are great spheres of ordinary materials such as metal, rock, water, ammonia and so on.  The only known force between any two planets, or between one of the planets and any person on Earth,  is gravity.  But the gravitational force between two bodies varies with the square of the distance. What this means is it is easy to demonstrate mathematically that the effect of a 150-lb obstetrician standing near a baby at birth is far greater than the effect of Jupiter on that baby.  

What does it mean that the gravitational force decreases with distance?  Let Brisban weigh in on the subject.  Click on his icon to the left for No Frill's Help.


If we assume that an unknown force similar to gravity is involved, but we simply haven't discovered it yet, then we still have a problem:  either the unknown force varies with distance, and we have the same problem we did with gravity where a small nearby object has much, much more influence, or the unknown force doesn't depend on the distance in which case distant stars and galaxies should have more effect than Mercury, Mars or any of the other planets.

The conclusion then is that the idea that the arrangement of the planets in the sky can affect or predict events on Earth is inconsistent with the modern scientific understanding the solar system.  Since consistency is a fundamental criterion of science, astrology is not a science, nor part of modern science.  It also fails to meet another criterion of science:  Astrology is rarely subjected to rigorous testing.

One of the most popular forms of astrology today is birth-sign astrology.  It is also one of the forms most easily tested.  A person born in the spring in the Iowa climate has different life experiences in the first year than someone born in the fall of the same year.  So there is a rational bases for asking whether birth-sign astrology has any basis in reality.  However, a number of years of testing birth-sign astrology with Astro 120 classes at ISU has yet to turn up any evidence that the time of year you are born affects your personality in any measurable way.

Now that we have discussed some of the differences between astronomy and astrology, you should never use the word "astrology" when you mean "astronomy".


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