- THE FIRST MILLENIUM
1543 – Poland
‘The Sun is at the centre of the solar system, fixed and immobile, and planets orbit around it in perfect circles in the following order: Mercury, Venus, Earth with its moon, Mars, Jupiter and Saturn’
The Copernican system defied the dogma that the Earth stood still at the centre of the universe – a concept that dated back to ARISTOTLE, which had been given observational legitimacy by PTOLEMY and authority by Christendom – and set forth a new theory of a Sun centered universe. Why would God create a hugely complicated system of equants, epicycles and eccentrics, as Ptolemy had used to explain planetary motion around the Earth, when it would be much more simple and graceful to have them all revolving around the Sun?
“Eight hundred years before Copernicus, a model of the solar system was advanced with the Earth as a planet orbiting the Sun along with other planets”
A few centuries later this idea fell into disfavour with the early Christian Church, which placed mankind at the centre of the universe in a geo-centric model. The alternative teaching would be deemed heresy punishable by death and it would not be until the seventeenth century that the work of GALILEO, KEPLER and NEWTON gave credence to the ideas revitalized by Copernicus in 1543.
Not only did Copernicus place the Sun at the centre of the solar system, but he also gave detailed accounts of the motions of Earth, the Moon and those planets that were known at that time. Between 1510 and 1514 he drafted Commentariolus, his initial exposition of the theory. In order to have credence, the idea required that the Earth itself be not fixed in position. He said that the Earth revolves on its own axis once every twenty-four hours, which accounts for day and night and explains the apparent movement of the stars and Sun across the sky. Copernicus suggested in Commentariolus that the time taken for each planet to complete its cycle through the night sky might increase the further it is from the Sun.
Mercury’s cycle takes 88 days, which makes it the nearest planet to the Sun. Venus takes 225 days, Earth 1 year, Mars 1.9 years, Jupiter 12 years and Saturn 30 years. Thus Copernicus was able to work out the truth and attempted to establish the order of the planets.
He did not publish his findings because they were thought to contravene the teachings of the Catholic Church. Religious leaders of his time were against him. Martin Luther (founder of the Lutheran Church in Germany) denounced him as ‘a new astrologer…. the fool’ who wanted ‘to overturn the entire science of astronomy’. His book De Revolutionibus Orbium Coelestium (On the revolution of the celestial spheres) was published at the very end of his life, and a copy placed on his deathbed. Thus the greatest astronomer of his time died without seeing his book in print – the book as influential as Newton’s Principia and Darwin’s ‘On The Origin of Species’.
The text was rejected by many academics; partially because the author had undermined the simplicity of his initial ideas by clinging to the Aristotelian belief that planetary motion took place in perfect circles. This meant Copernicus had been forced to introduce his own system of epicycles and other complex motions to fit in with observational evidence, thereby producing as equally complicated an explanation as the geocentric one he had initially rejected for its lack of simplicity.
It was not until Johannes Kepler offered the solution that the planets move in an elliptical, not circular, motion in 1609 that the simplicity that Copernicus had been seeking was offered and the rest of the model could be vindicated.
In fact, it was not until 1616 that the Church banned the text Copernicus eventually published for its ‘blasphemous’ content, although that sanction remained in place until 1835.
1621 – Holland
‘During refraction of light, the ratio of the sines of the angles of incidence ( i ) and refraction ( r ) is a constant equal to the refractive index of the medium’
In equation form: n1sini = n2 sinr , where n1 and n2 are the respective refractive indices of the two media.
The refractive index of a substance is a measure of its ability to bend light. The higher the number the better light is refracted. The refractive index of diamond, 2.42, is the highest of all gems.
Refraction is the change in direction of a ray of light when it crosses the boundary between the two media. It happens because light has different speeds in different media. A ray of light entering a medium where the speed of light is less (from air to water, for example) bends towards the perpendicular to the boundary of the two media. It bends away from the perpendicular when it crosses from water to air. Refraction was known to ancient Greeks, but Snell, a Dutch mathematician, was the first to study it.