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Galileo

July 1, 2010

In the first decade of the 1600s some amazing observations were made that challenged, and ultimately changed, humanity’s ideas about the nature of the universe. These were partly made possible by the invention of the telescope and a series of discoveries by Galileo, but he was building on a lot of important work that had been going on since the time of the ancient Greeks.

Copernicus had formed and published his theories in the first half of the 1500s. He proposed using a heliocentric model of the solar system (the sun being at the centre, with the 5 planets rotating around it). In a preface to the work that put this theory forward it is said that this model should be used to make calculations more accurate rather than as a model of how the solar system actually behaved. This was an age when disputing the established doctrines of the (catholic) church wasn’t such a good idea.

The church worked with a system of natural philosophy synthesised by Aquinas. He had combined Christian theology with Aristotelian philosophy. There were five elements; earth, air, fire and water and “quintessence”. There was no concept of inertia. Stars and planets orbited a fixed earth in perfect circles, and were made of the element quintessence. They were perfect, divine and unchanging. The sun was a symbol of god and his perfection.

Some of these concepts obviously didn’t sit well with the mathematical calculations that were being carried out by astronomers in early days of astronomy, so Copernicus’s model was a useful tool for natural philosophers – as long as they didn’t admit to believing that was how the planets actually behaved. Apart from the discrepancies between observation (carried out with the naked eye) and calculation, there was little evidence to show how wrong the traditional explanations were.

In 1604, a new star appeared. It was studied by Kepler (without the aid of a telescope), and is now know as Kepler’s supernova. Even before the invention of the telescope, Galileo had used this in a series of lectures as evidence that the Aristotelian theories, in part, weren’t correct – the stars do change. Undeniable evidence emerged when Galileo turned a telescope towards the sky.

  1. Moons orbiting Jupiter. If there were bodies orbiting something other than the Earth, we obviously aren’t at the centre of all those perfect circles of orbits.
  2. Mountains on the Moon – it obviously wasn’t made of something quite as perfect as was thought, and in fact had features that looked remarkably similar to those on our planet.
  3. Sun spots. The Sun also wasn’t perfect – it had blemishes, and obviously this wasn’t consistent with either the concept of quintessence or of the sun’s divine meaning.
  4. Stars not visible with the naked eye. If the universe was created for the purpose of housing humans, why was there some of it that was inaccessible to us unaided?
  5. Phases of Venus. The phases were only explainable if Venus was orbiting the Sun, rather than the Earth.

These observations were a devastating blow to the theories at the time (although when they were first published little fuss was made by the Church). Galileo had shown that the dominant theories were not supported by empirical observations. But he hadn’t necessarily shown that the Copernican model of the solar system was entirely correct. His answer to this came later, when he was again observing the moons of Jupiter. He noticed that there were some anomalies in the data he had gathered and, more importantly, he realised that the way to explain these was assume that Earth and Jupiter were orbiting the Sun.

This wasn’t just a way of making the maths work. Galileo had shown, through observation, that the Copernican theory was true, correctly describing the physical behaviour of the solar system. It still wasn’t too sensible an idea to vocally profess a belief in Copernicanism, but once the theories started spreading it was inevitable that conventional “wisdom” would catch up with reality.

[Thanks to Justin for spotting spelling mistakes, hopefully sorted now…]

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2 Comments leave one →
  1. July 17, 2010 8:39 PM

    Wasn’t Gallileo labled as a heritic By the Catholic curch For his discoveries?

  2. July 17, 2010 9:05 PM

    I’m not entirely sure – in all that I’ve heard and read over the years this isn’t made explicit. What is clear is that church was much more lenient than is generally supposed.

    Galileo published the findings that I listed in 1610, the year after his discoveries. His first scrape with the church wasn’t until 1616, when he signed a statement that he wouldn’t teach Copernicanism. After that, he had a not un-friendly relationship with the church, including audiences with one or more popes. His actual trial was in 1633 – over 20 years since his publication. The end result of this was that he recanted his professed belief in Copernicanism as a model for the actual behaviour of the solar system and was sentenced to life imprisonment (although by all accounts this was a relatively easy house arrest in Arcetri, a suburb of Florence). Nowhere in this, as far as I can tell, was Galileo expressly labelled a heretic.

    A quick google leads me to this reference in a footnote on wikipedia (ok, not the best source of references…). Looks like it might be worth a read.

    http://en.wikipedia.org/wiki/Galileo_Galilei#cite_note-103

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