Heliocentrism (Part 1)

Gussie Coulter

The heliocentric model of the solar system is that in which the sun, orbited by the eight planets, is situated at the centre of our solar system. Despite being the conventionally accepted model of the solar system in the modern world, it has had a problematic and, to be frank, an incredibly rocky history; from epistemic oppression, to human rigidness to an unimaginable degree, to having been established and then forgotten, the history of the conflict between the geocentric model – in which the Earth is at the centre – and heliocentrism is fascinating. Whilst the way in which astronomical bodies traverse the sky has been subject of human thought since at least the Third Millenium BC, heliocentrism has only taken hold within the last 500 years. Prior to the Copernican Revolution, humanity was grounded, stuck in an egotistical geocentric universe. The irony of the matter is that heliocentrism may have actually taken its roots a little over 2000 years ago in the Aegean Sea…

A 17th Century illustration of the Copernican model of the solar system by Andreas Cellarius in his star atlas 'Harmonia Macrocosmica'.

A statue of Aristarchus of Samos located at the Aristotle University of Thessaloniki.

Enter Aristarchus of Samos:

The region of Ionia, a small archipelago off the coast of, and including parts of, modern day Turkey, seems like an unlikely place for scientific discovery. Being at ‘the crossroads of civilisation,’ as described by the great Carl Sagan, Ionia was not subjugated to oppression of radical scientific thought due to its vast cultural mixture. As the sun was beginning to set on Ionia as the primary scientific hub and its pivot to Alexandria was taking place, the first known example of a heliocentric model began to take shape.

Aristarchus, born around 310BC on the Ionian island of Samos, much like his Ionian contemporaries, took a liberal and radical approach to our understanding of astronomy. Whilst his original texts were lost, Aristarchus is thought to have been the first to posit the heliocentric model of the universe – according to Archimedes in The Sand Reckoner Aristarchus’ hypotheses were that “the fixed stars and the sun remain unmoved, that the earth revolves around the sun on the circumference of a circle, the sun lying in the middle of the orbit”. Very reminiscent of what we now know is true. Not only were his views insightful, but they were grounded in empirical observation, most notably in his view, likely adopted from Anaxagoras, that all stars were merely suns at a great distance; He established that the lack of a parallax (difference in apparent position when changing line of sight), was indicative not of the fact that there was an ethereal sphere of ‘fixed stars’ but that stars were, in fact, incredibly far away. The previous conception was that the stars and other observable celestial bodies were embedded within heavenly, spherical shells encapsulating the earth as will be discussed below.

Whilst many classical scientists and philosophers, by the likes of Plato, Aristotle and Ptolemy (though a little later) preferred the geocentric model, surprisingly Aristarchus was not oppressed. The sacriligeous nature of heliocentric models seems to be a slightly more modern phenomenon. However, due to the massive popularity and support for the geocentric model, Aristarchus’ ideas were largely forgotten. It may be that Aristarchus is the unsung hero of heliocentrism.

The geocentric model takes hold:

Despite the early theories of a heliocentric model, they entirely failed to gain traction. In addition to this, further efforts were put into finding scientific evidence and justification for the assumed geocentric model.

From well before the time of Aristarchus, advocates of the geocentric model had devised that, in order to explain the observed movement of astronomical bodies in the sky, such as planets, stars, the moon and the sun, the earth was enclosed within so-called ‘celestial spheres’ or ‘crystals’. This spherical, geocentric notion, held by many, was advocated and developed by the likes of Pythagoras, Plato, his student Eudoxus, Aristotle and most other notable philosophical and scientific figures of the ancient world. The ultimate blow, or rather inhibition, of the heliocentric model was as a result of the remarkable work of Ptolemy, a Roman astronomer and mathematition of the 2nd Century AD. Ptolemy was from Alexandria, the centre of scientific thought and development of the ancient world. As such, he quickly came to be a great intellect, producing many scientific treatise which would shape the world forever. One, however, advocating the geocentric model of the universe, the Almagest offered highly convincing mathematical, geometric modelling for the ‘celestial sphere’ view of the universe.

An illustration of the 'celestial sphere model'. You can see the perceived orbits of the planets such as Mars (‘Martis’).

A diagram including the deference (the large circle), the epicycle (the small circle) and the observed path (the squiggly line).

The ‘celestial sphere’ model held that the Earth was enclosed by a series of rotating spheres constituted by ‘quintessence’ and that encrusted within each were astronomical bodies. In medieval and ancient philosophy, the Earth was constituted by four elements or ‘essences’. ‘Quintessence’ was the extraterrestrial fifth element that was transparant and was deemed to be spiritual or heavenly. As such, there was a designated sphere for each planet, for the sun, for the moon and a singular sphere for all the ‘stationary stars’. Ptolemy was able to fine-tune this spherical view of the universe mathematically in order to account for the discrepancy between the older ideas and empirical observations, particularly the ‘apparent retrograde motion’, the tendency for Mars to form a looped path as it traversed the sky, a product of the different orbits of Earth and Mars about the sun. In the Planetary Hypotheses Ptolemy incorporated into the orbit of the celestial bodies two components: the deferent and epicycle. The deferent constituted the main orbit of the body about the earth and the epicycle is a much smaller circle about which the body moved during its journey around the deferent.

Due to the accuracy with which Ptolemy was able to model the percieved spheres and the orbit patterns, it is really no wonder why it was effectively scientifically canonized. Such geocentric thought, backed with Ptolemy’s observation and rational thinking shows just how natural an Earth centered universe would have been to a person of the time. This very fact, and in particular its adoption by Roman Catholic doctrine hindered the development of heliocentric thought to the extent that it took around 1400 years to resurface.

To Be Continued Next Issue...

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