FEATURE: Heliocentrism

 Heliocentrism
 

Finally we shall place the sun himself at the centre of the universe

Nicolaus Copernicus

 

It is surely harmful to souls to make it a heresy to believe what is proved

Galileo Galilei

Since as far back as 270bc it has been posited that the sun is in the centre of the solar system.  The idea didn’t catch on until the 17^th century when a complete heliocentric theory emerged. At the time the church had a lot more influence and since the bible seems to point to a geocentric model that is what the prevailing theory was.  Heliocentrism shattered our world view mankind was no longer literally the centre of the universe.

                In antiquity models of the cosmos placed earth at the centre with everything radiating outward from there, the orbits executed perfect circles. Philosophers were attracted to the idea that nature favoured perfect geometries as more accurate measurements where made there clockwork mathematical descriptions increasingly failed to explain them.  It wasn’t until Kepler that these perfect circles where replaced by the more correct ellipses. The ancient Greeks believed that all the heavenly bodies were affixed to crystal spheres that spun about the Earth causing the stars pinned upon them or revealed through tiny holes within them to circle the north and south celestial poles each night.

                The idea that the heavens revolve about the sun rather than the Earth a heliocentric model, after the Greek word helios for sun, was suggested by ancient Greek philosophers as far back as Aristarchus in 270bc who conveyed such ideas in his writings.  After calculating the relative sizes of the earth and the sun Aristarchus realized the sun was much larger it made more sense to him that the smaller earth would move rather than the larger Sun.

Ptolemy

                In the second century Ptolemy used mathematics to predict the motions of the stars and Planets.  He did so reasonably well but; there where patens that his equations could not match.  Most puzzling of all is that the planets seemed to change direction. Ptolemy believed , like many of his contemporises, that the planets literally turned on giant wheels in the sky.  He invented an explanation for the retrograde motion by adding extra cogs to their orbits. Theses superimposed epicycles gave the appliance of the planets occasionally looping backward.

Copernicus

                Born in Torun Poland Copernicus trained as a cannon taking classes in law, medicine, astronomy and astrology he was fascinated by but critical of Ptolemy’s ideas about the order of the universe.  Copernicus worked out his own system where the earth and the other planets rotate around the sun he published this theory in his work ‘On The Revolutions of Heavenly Spheres’ published just two months before he died. Ideas like this were occasionally mooted over the centuries but not taken seriously.  So it was not until the 16^th century that the consequences of the sun central model were fully developed.

The established church and society in general favoured Ptolemy’s geocentric view.

Galileo

Galileo Galilei notoriously challenged the roman catholic church by championing heliocentrism.  He backed up his audacity with careful observations made through the newly developed telescope.  Galileo found evidence that the earth was not central at all, that Jupiter has moons orbiting it and that Venus has phases like the moon.  He published these discoveries in his book starry messenger having made the audacious clame that the suns apparent migration across the sky was simply down to the earth’s rotation he found himself summoned to Rome. Despite the fact that Galileo’s observations where backed up by Jesuit astronomers the church refused to accept galilos theory.  Stating that although it was appealing in its simplicity that the theory could not be taken literally. Although restricted Galileo remained certain that his Sun cantered explanation was true, asked by Pope Urban VIII to write a balanced account of both sides in a ’dialogue of the two world systems’ Galileo upset the pontiff by expressing a bias for his own view over that of the church.  He was summoned back to Rome and put on trial for breaking his ban and placed on house arrest for the rest of his life.

Kepler

Meanwhile German astronomer Johannes Kepler was also working on the mathematics of planetary motions. Kepler published his analysis of the path of Mars in his 1609 book Astronomia nova.  Kepler found that an ellipse rather than a circle gave a better description of the red planets orbit around the sun.  now considered to be a basic law of physics Kepler’s vision was advanced for its time and took a long time to be accepted, Galileo for one took no notice.

Gradual acceptance

Evidence of the fact of heliocentric theory accumulated over the Century’s.  Kepler’s mechanics of orbits influenced Newton’s theory of gravity, as further planets were discovered, the fact that they orbited the sun was obvious. Man’s place at the centre of things is no longer tenable

270bc	Ancient Greeks propose sun centred model
200	Ptolemy adds epicycles to explained retrograde motions
1543	Copernicus publishes his heliocentric model
1609	Galileo discovers Jupiter’s moons.  Kepler models orbits as ellipses
1633	Galileo put on trial for teaching heliocentrism