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Moving to the Mullard Radio Astronomy Observatory at Lord's Bridge


The beginnings of radio astronomy (Part 3)
Antony Hewish Astronomer
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It all happened so rapidly from very… very small beginnings and it was really a rather strange world. The fact that with such… simple equipment you could… you could make observations of cosmological importance quite… quite rapidly and, having discovered that these things were distant galaxies, Martin Ryle then, of course, began to realise that there were far too many of them and they followed the wrong distribution in space for a steady state universe. One of the nice things about the steady state theory is that it’s easily contradicted by observation, if you have… if you have a cosmology in which the universe is replenishing itself, it’s… it’s reached a very fine state of balance, and that means that in large scale space as you look to further and further distances, you’re just looking back in time. But if the universe has been there forever and is going to continue forever, just like a changing population of people, but always the same number of people, people being born, people dying, galaxies being born and galaxies dying, then when you look to greater distance you ought to see a universe that’s very like the universe close to you. And when Martin Ryle started doing the statistics of that, he found out that there were far too many radio galaxies, as we then called them, in the more distant parts of the universe. And he saw then that the steady state theory must be wrong and that’s when he got his major cosmological interest going.

But… but for the first few years here, on our site, we were making more and more surveys and the idea that we could actually see what the radio galaxies were, as in an optical faded photograph, that was just nowhere near because you couldn’t get a sharp enough angular resolving power. But Martin Ryle always was thinking well ahead of what… of what he was actually doing and it was the early 50s when he realised that this work had to be extended with instruments of higher sensitivity and… and resolution that he hit on this idea of… of aperture synthesis. The… Bernard Lovell was then planning his 250-foot dish, which was going to be immensely expensive and take him years and years to build, and in the end not really be good enough because the biggest dish you could conceive of then was… was a few hundred feet across. And that was going to be an immense project, as… as we know Jodrell Bank was. And Martin Ryle was a bit scornful because he thought, well, if you don’t adopt conventional antenna building principles, but go for this technique of extending interferometers and moving them about and… and linking up the data from different… adding the data from different positions, that would give you a way of synthesising a huge telescope that you couldn’t possibly build. And it wasn’t… well, in fact, the term aperture synthesis, I… I invented that myself because I helped Martin Ryle write some of his first papers. I wasn’t involved with the fundamental ideas here, but Martin Ryle was always far too busy actually dreaming of the future than… than he was in… in writing up his work. And I did some work on… on the background of aperture synthesis, which had been demonstrated by a graduate student, John Blyth, the great footballer. Did you know John? No, you wouldn’t have known that he was a footballer, perhaps… I know that you’re interested in football yourself. John Blyth demonstrated the principle just a few hundred yards from where we’re sitting, moving at dipole north-south and having an east-west array and… and doing the very first synthesis on EDSAC 1, the computer which was so elementary that it took hours to do the simplest Fourier synthesis.

But at any rate, the principle had been proved and Martin Ryle said, ‘Well, we will begin to think about a much larger instrument’. He then was using conventional reflectors, not in the synthesis mode but as in a Michelson interferometer mode and that gave the first major surveys of the sky which ran the 3C survey, which is a… which is a famous survey in the history of radio astronomy. It went through various versions, becoming more accurate as time went on, but it located two or three hundred accurately located radio galaxies, which optical astronomers could then attempt to identify, and some of them were identified with distant galaxies and others were not, and so on. But that’s when the cosmological story began and, in order to extend all that, Martin said, well, it’s stupid to build a fixed dish which is… I mean, a steerable dish which is 250 feet across because, a) it’s going to be expensive and, b) it won’t do the job. I mean, it had sensitivity but it didn’t have the angular resolving power and you can’t do very much with an angular resolving power which depends upon the diameter of the dish and the dish is only 250 feet. He said, we want a dish which is a mile across, or thereabouts, and that’s when the aperture synthesis began and… and in 1957, to develop this properly, we moved out to Lord’s Bridge Observatory.

Born in 1924, Antony Hewish is a pioneer of radio astronomy known for his study of intergalactic weather patterns and his development of giant telescopes. He was awarded the Nobel Prize for Physics in 1974, together with fellow radio-astronomer Sir Martin Ryle, for his decisive role in the groundbreaking discovery of pulsars. He also received the Eddington Medal of the Royal Astronomical Society in 1969.

Listeners: Dave Green

Dave Green is a radio astronomer at the Cavendish Laboratory in Cambridge. As an undergraduate at Cambridge his first university physics lecture course was given by Professor Hewish. Subsequently he completed his PhD at the Cavendish Laboratory when Professor Hewish was head of the radio astronomy group, and after postdoctoral research in Canada he returned to the Cavendish, where he is now a Senior Lecturer. He is a Teaching Fellow at Churchill College. His research interests include supernova remnants and the extended remains of supernova explosions.

Duration: 5 minutes, 55 seconds

Date story recorded: August 2008

Date story went live: 25 June 2009