Tim Radford 

How three wise men and a tube helped us find our place in the universe

Science Book Club: Tim Radford nominates Seeing and Believing by Richard Panek as the definitive guide to the revolution wrought by the telescope
  
  

Galileo's telescope
Galileo, Copernicus and Kepler between them overturned the church's perfect celestial order. Photograph: Hulton Getty Photograph: Hulton Getty

The telescope changed our lives, and this book is about how it happened. Seeing and Believing tells only a fraction of a 400-year-story, and – since it was written in 1998 – it cannot even hint at the last decade of eye-opening discoveries. It is furthermore a very short book, so its scope is constrained. If you want to know how to design, fabricate and use your own telescope, this book will be no help.

But Seeing and Believing is still my candidate for the best introduction to this founding instrument of the scientific revolution. The key words in the subtitle are "how we found our place in the universe", and Panek's account reminds us in short and vivid ways of the disorderly progress of scientific discovery. For instance, we learn that Galileo did not "invent" the telescope in 1609, as is popularly supposed, nor was he even the first to think of using it for scientific exploration. Roger Bacon had predicted the "wonders of refracted vision" in 1267 and, more than three decades before Galileo, at least two writers had described peering into the distance with the aid of lenses.

Nor was Galileo the first to look at the heavens through a spyglass: the Englishman Thomas Harriot beat him to it by months, but failed to tell anybody. But in November 1609 Galileo began to use two lenses in a cylinder to look at the moon, Jupiter and the sun, and recognised the significance of what he saw. He saw that the moon's topography was Earth-like, that Jupiter had moons and that the sun had spots.

This was all very unorthodox and heretical, and Panek offers a vivid snapshot of the medieval cosmology that Copernicus, Kepler and Galileo between them overturned: the celestial order in which an imperfect Earth was the centre of the universe, and the moon, sun and stars revolved about it, set in perfect, crystalline spheres of increasing moral excellence.

The planets – the "wanderers" – required a bit of explaining, which is why the story starts with them. And if the moon had mountains and seas, like Earth, then it wasn't as "heavenly" as had been supposed. If Jupiter had moons revolving about it, then it had something in common with Earth: they were both planets. And the "wandering" of the planets made geometrical sense if the Sun was the centre of creation, rather than the Earth.

Why should we believe long-dead authorities such as Aristotle and Ptolemy when our eyes tell us something different? Why rely on ancient authors when we can open the book of nature and read a different and better story?

The revolution proceeded erratically, but within two generations amazing things had happened. The first telescopes presented problems of focal length, chromatic aberration, narrow field of view and so on. You could see planetary furniture that you had never seen before, but the stars remained enigmatic points of light.

Galileo, with a smugness that his contemporaries must have found ever so annoying, was convinced he had discovered almost all there was to discover: "It was granted to me alone to discover all the new phenomena in the sky and nothing to anybody else."

Some people, including Christopher Wren, believed him. Some people continued to believe that the naked eye was a better instrument than two lumps of glass in a tube. But the new community of lens-grinding astronomers got on with the challenge. If the sun was the centre of our world, how far away was it? If light was the agency of discovery, was it instantaneous, or did it move? If so, how fast did it move?

In 1676, less than one lifetime on from Galileo, the Danish astronomer Ole Romer predicted an eclipse of a Jovian moon, and having calculated the changing orbital locations of the Earth and Jupiter at that time, boldly claimed that the eclipse would be visible 10 minutes later than expected. He was dead right, and he used the result to settle the matter: light moved, at a speed of 140,000 miles a second. Given the quality of the clocks and observing instruments of the day, that was pretty close to the true figure.

To make such a calculation, he and other astronomers had to have an idea of the diameter of the Earth's orbit, and they got a good ballpark figure in the same decade. By 1728, the English astronomer James Bradley had used this value for the Earth's orbital journey to try to calculate the distance to a star by observing from two separate points. Look at something first with one eye covered, and then the other, and see how the observed object seems to move. The apparent shift in position is called the parallax, and the nearer the object the bigger will be the parallax.

From his standpoint on the Earth in orbit, Bradley tried to measure the stellar distance by making observations six months and therefore (we now know) 186 million miles apart. He could detect no apparent movement, but he used this negative result to calculate that, because he could observe no parallax, therefore the nearest star (apart from the sun) must be at least 36 trillion miles away.

So, in less than two lifetimes, astronomers already had a grasp of the depth of space. Heaven wasn't a "vault", it was somewhere that went on and on. They also rather gave up on the stars until the Hanoverian William Herschel came along and with the innocence of the amateur, built better telescopes and looked at the whole sky, spotted Uranus, discovered infra-red radiation and formulated in a sentence the significance of a finite value for the speed of light: "A telescope with the power of penetrating into space, has also, it may be called, a power of penetrating into time past."

By 1859, someone had used a spectroscope to identify the elemental make-up of the sun; by 1888, a camera fitted to a telescope had collected enough light to discern the spiral structure of Andromeda; and within another lifetime, Edwin Hubble had confirmed that the Milky Way galaxy wasn't the beginning and the end of the universe, it was just a speck of matter in the enormity of everything.

The story goes on, and Panek's version of it reminds us that such revolutionary discoveries arose from a worldwide, non-stop, free-for-all of competing, collaborating and communicating enthusiasts, who often bickered, but also generously exchanged their data, their ideas, and their techniques.

We have an "exaltation" of larks and a "charm" of finches, but what's the right collective noun for a bunch of astronomers? How about a focus group?

In the querulous crossfire that followed last month's book on race, IQ and dubious anthropology, @EndPseudoscience suggested that club members might look at a book by Jared Diamond which "explains this subject very well."

Thanks, EP, the club will be back in February and the next book is indeed Guns, Germs, and Steel by Jared Diamond

 

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