Not in the middle

Ken Tapping's weekly astrophysics column from the Herzberg Institiute on White Lake Road


One of our stranger traits as human beings is our willingness to hang passionately onto ideas in the face of increasing and eventually overwhelming evidence they are wrong. A good example is our reluctance to give up the belief that our Earth is the centre of everything, with the Sun, Moon, planets and the rest of the cosmos circling round it.

To our ancient ancestors it was obvious. The Sun, Moon, stars and planets all rose in the east and set in the west. We could not feel the Earth moving, so it was common sense that everything in the sky was circling around us. As a rough and ready picture of the universe it worked. Since the idea of our centrality in Creation lay at the core of many religious beliefs, our Earth-centric picture became “Official”, with little future in arguing with it.

However, as astronomical instruments improved, and the data got better and available in large quantities, problems appeared. One of the most serious came from the planets. When measuring their changing positions with respect to the background stars, their motion turned out not to be what we would expect if we are looking at something circling around us. If that were the case, we would just see the planets moving smoothly, in one direction; instead we see them suddenly doubling back, making a loop and then resuming their original direction. On the other hand, this is exactly what we would see if we are on a planet circling around the Sun, looking at the other planets, which are doing the same thing. We have all been on a roundabout sometime or other. Remember how our surroundings behaved as we were carried round and round?

In the 16th Century Nikolaus Kopernikus proposed that the Earth and other planets circled the Sun, but dared not publish his results until he was about to die. Galileo suggested the same thing in the early 17th Century and ran into problems with the religious establishment. Unfortunately for the authorities, the cat was now out of the bag and the new vision of the cosmos was spreading rapidly across the world. Later that century, Johannes Kepler put the sun-centred view of the Solar System onto even firmer ground. Then still in that cosmologically explosive century, Isaac Newton formulated the theory of gravity and provided the tools to put the motions of things in the sky on a firm, mathematical basis.

In the 14th Century, William of Ockham came up with one of those blisteringly simple ideas that are useful guides today. It is now known as “Occamís Razor”. Basically this involves cutting ideas down to their bare essentials, and if one can explain something using simple, known things, there is no need to invoke unknown things. Start with the simplest solution. However, it is fascinating to see how we are also very good at avoiding such wisdom.  Some of the ideas concocted to explain what we see in the sky while keeping the Earth in the centre of everything must have had William spinning in his grave. Of course today we are more logical and scientifically aware, and no longer passionately hang onto failed ideas. Is that true?

Look for Mars, appearing low in the dawn twilight. Venus and Mercury lie close together in the sunset glow. Saturn is high in the southern sky.  The Moon will reach last quarter on the 29th.

Ken Tapping is an astronomer with the National Research Council’s Dominion Radio Astro-physical Observatory, Penticton.