Jim's Blog
Four Hundred Years of Astronomy

Tuesday, 14 July 2009

Well, so much for a regular blog. Anyway, better late than never. So what have I been up to these past few months (I pretend to hear you ask)? Well, throughout March to end of June I was pretty much working flat out on my book (The House of Wisdom). It is now finished and submitted to Publishers, Penguin. Hopefully, all systems go for publication next Spring in time for London Book Fair. At the same time, I was filming for the new Channel 4 series "Genius of Britain" - No, not me! It is a series about the greatest names in British science, and is due out next year. Then, as of end of June I started filming my new series for the BBC on the history of Chemistry. This will keep me busy until the end of the Summer so I guess not much chance of any hols. Oh, and Episode 4 of my podcast "Jim Al-Khalili's SciPod" is now out and available on iTunes.

Anyway, the subject of this blog is a timely reminder of this year's big science celebrations. Not only is it Darwin200 and International Polar Year, it is also International Year of Astronomy (oh, and it is the centenary of the discovery of the atomic nucleus by Ernest Rutherford). But it is the astronomy angle I wish to say something about.

It was during the summer of 1609 that Galileo first pointed his newly invented telescope towards the heavens and confirmed one of the most important ideas in the history of humanity: that we are not at the centre of the Universe. This year we celebrate the 400th anniversary of that discovery as International Year of Astronomy. Of course, astronomy, unlike many other areas of science, is not difficult to sell to the general public as an exciting and fascinating subject, but its history has often been incorrectly told.

For many historians of science, it was the Polish astronomer, Copernicus, who ushered in the age of modern astronomy. For it was he who gave us the modern picture of the solar system with the earth as just one of a number of planets orbiting the sun, rather than the other way round. This 'heliocentric' model is what Galileo was to confirm nearly a century later. But it was Galileo rather than Copernicus who is the true father of modern astronomy.

Firstly, Copernicus was not the first person to propose a heliocentric model. The Greek philosopher, Aristarchus, had done so in the third century BC, but no one believed him apart from a Babylonian astronomer by the name of Seleucus. The great Greek physicist, Archimedes, wrote the following about Aristarchus: "You know that most astronomers designate by the word cosmos the sphere whose centre coincides with the centre of the earth... But Artistarchus the Samian, published in writing certain hypotheses in which it follows that the cosmos must be many times greater than the one mentioned before. He assumes namely that the fixed stars and the sun remain stationary, while the earth moves round the sun through the circumference of a circle." Then, during medieval times, several Muslim astronomers tried to revive the heliocentric idea, but most of them were so influenced by the likes of Aristotle and Ptolemy who preached that the earth was at the centre of the Universe that the correct cosmology never caught on until Copernicus.

Secondly, like all astronomers before him, Copernicus came up with his new theory based on observing the night sky with the naked eye. He also had no notion of the concept of gravity, for that was to come much later with Newton. Therefore in many ways his 'cosmology' was not very different from those that had come before. He still believed that the sun was at the centre of the whole Universe rather than just the solar system.

Finally, it is interesting to note that Copernicus used mathematical techniques developed several hundred years earlier by Muslim astronomers like the 13th century Persian al-Tusi and the 14th century Syrian Ibn al-Shatir. Scientific progress is a continuum. It was Newton who said that if he saw further than others it was because he stood on the shoulders of giants. Thus, astronomy did not start with Copernicus or Galileo, just as physics did not start with Newton.

Still, the telescope revolutionised our understanding of the cosmos, just as the microscope was to revolutionise our understanding of the microcosm. So we have every right to celebrate its 400th anniversary this year, for without it we would still be stuck with abstract metaphysical speculation about our place in the Universe.