Why the earth should be the centre of the solar system

Corlett Novis
Dec 31, 2018 · 4 min read
Ptolemaic Armillary Sphere, by John Rowley, London, c. 1700 (Oxford History of Science Collection)

The object pictured above, an armillary sphere, is a symbol of geometric order and beauty. It is a physical model of our universe with the Earth at the centre and with every ring moving outward at regular intervals representing each of the heavenly bodies in their observed order: the moon, Mercury, Venus, the Sun, Mars, Jupiter, Saturn and, finally, the stars which are fixed in place as constellations.

As anyone with a jot of astronomical experience will tell you, there are plenty of things wrong with this model. Not only are planetary orbits actually elliptical rather than circular, and not only are they missing Neptune and Uranus, but the order of the planets is also entirely wrong because the Sun is the true centre of the solar system, not the Earth!

The construction of this sphere, in around the year 1700, happened soon after a tremendous revelation in the astronomical community: that the planets orbit the Sun and no the Earth. The model represented by the sphere depicted above, with the Earth at the centre, had only recently fallen from popularity. Up until this time astronomy had been entirely constructed around this false model, known as “Geocentrism” (meaning “earth-centred”). Furthermore, as a result of their primitive optics, not only were they ignorant of the existence of certain planets, moons and the rings of Saturn, Astronomers before the second half of the 17th century would also have found the concept of ellipses inconceivable and, when proposed, unacceptable.

Before mankind came to realise that the Sun is the true centre of our solar system, we operated in a system which preached its views as dogma and which seemed, to all appearances, to be more true because of its beauty. This system was called “Ptolemaic astronomy”. This ancient Greek system held that the planets moved in regular, circular motions since the heavens were perfect and since circles were considered a perfect shape. They also held that the earth was at the centre because we are the most significant part of creation. But what made this theory so convincing was the compelling visual evidence demonstrated in this armillary sphere: a perfectly ordered solar system.

The other option available at this time, and the system which would ultimately win out in spite of its unattractiveness, was the Copernican model. Contrary to popular belief, Copernicus’ heliocentric model (an astronomical model with the sun at the centre) did not originally provide a dramatically more accurate model than the Ptolemaic one. Although Copernicus had managed to do away with some of the more contrived aspects of placing the earth at the centre, his system ultimately proved every bit as complicated to understand and calculate while at the same time, sadly, looking far less appealing.

A second armillary sphere demonstrates the dramatic loss in geometric beauty and regularity in the Copernican model:

Copernican Armillary Sphere, by John Rowley, London, c. 1700 (Oxford History of Science Collection)

To the modern scientist, the geometric symmetry, regularity and beauty of a theory don’t make it correct. Rather, it must simply conform to and explain the evidence. To the scientists before the 17th century, however, this was not at all the case. Influenced strongly by the cosmology of Plato and Aristotle, scientists believed that the universe was a very orderly place and that theories which seemed the most beautiful and mathematically pleasing were more likely to be true. Looking at both armillary spheres, it's not difficult to see why the first, for a long time, won out over the second: it just looks neat and tidy.

In summary, much of what we take for granted to be “obvious” about the universe simply isn’t so. The knowledge we are gifted with in the modern age is often very counter-intuitive and required a sustained commitment to critical inquiry. This example of our solar system illustrates the compelling nature of only one dead theory, but there are many others too. Vitalism, anthropocentrism, and even phlogiston theory were all incredibly compelling in their own times. What this demonstrates is that the most obvious answer isn’t always best and that science is a far messier process than it often portrays itself to be today.

Meaning of the Method

Stories investigating the sciences

Corlett Novis

Written by

Editor at Pi Media (London) interested in Science and Technology and how they interact in wider society and culture.

Meaning of the Method

Stories investigating the sciences

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