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Work leading to the discovery of quasars


Studying radar echoes from the Moon
Bernard Lovell Astronomer
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During the course of the construction, this work continued. Hanbury Brown and Hazard... they... they continued their measurements on the distribution of radio emissions of the galaxy using the 280 foot transit telescope and we also developed a system for studying the radar echoes from the moon, which turned out to be fascinating. We were not the first to succeed in getting radio echoes from the moon. Quite a history attached to that which you will find in the history books.

I think the first observations were claimed to have been made by a person called Z Bay in... in Hungary, I think. He used the walter voltometer and claimed that he heard echoes from the moon. I think he was probably correct by observing this walter voltometer. We were amongst the first to make a... a detailed study of the radio echoes from the moon, and the Australians had also done some work on this. And if one does observe radio echoes from the moon on frequencies in the meter wave band, there're two things that immediately become obvious, one is that you do not get a steady response. There are fluctuations of signal strength.

Now, there are two... you can immediately distinguish two types of fluctuation. There's a rapid fluctuation of periods of seconds or minutes and there is a long period of fluctuation imposed on this of the order of 30 minutes or so. Now, the Australians had concluded that the short periods of fluctuations were occasioned by the... by the libration of the moon in its orbit. That is the slight oscillation as it moves in... in orbit round the earth and I... we confirmed that. There was no question this was the case, and then one day, Murray, who was working on this problem, he phoned me and I think it was the weekend, I was here and he said... he... he was pretty certain he had found the solution to the problem of the long period of fading. And so we... we... I encouraged him to set up a special system in the yagis in... in Echelon where the moon... so that the moon could be observed for about half an hour or longer without moving the aerial. And it... it turned out that he was correct and it was not difficult to prove the long period of fading was not really associated with the moon itself but was occasioned by Faraday rotation in the ionosphere.

Now, I think also in the 1950s, this... when the telescope was being built, this work on the moon was extended by a young student who was JV Evans. Now, JV Evans... he turned out to be quite an exceptional young man and he took over the observation of the radio echoes from the moon. Now, he... he was quite... he was keen enough to notice several things during these observations. One important... one was that the intensity of the reflection of the signals from the moon did not coincide with what one would expect, knowing the area of the surface of the moon which our beam was covering, and he carried out quite a... quite a brilliant series of observations dealing with this matter. And he... he reached the remarkable conclusion that the... whereas if you look at the moon in... in ordinary light, it is... it is uniformly... it's a uniformly bright disc.

On the other hand, if you look at it with... on a wavelength of a few metres, it is... it is limb darkening. In other words, the effect of reflection of radio waves from the surface of the moon takes place, as Evans discovered, on only about the first third of the... of the centre of the diameter of the moon. Now, this turned out to be very interesting for another reason, and that is that up to about 1,000 megahertz or thereabouts, the... the reflection for the surface of the moon which was being limb darkened would be... would be pretty coherent and that... that is how it became possible to speak into a microphone and send a signal to the moon and hear one's voice coming back again.

Now, again, I don't think we were the first to get our voice reflected from the moon. I think it was a person called Trexler in America who did this, but anyhow, when the telescope came into use in 1957, 1958, I went into the swinging laboratory underneath the bowl of the telescope with Evans and made a recording of us saying, 'Hello, moon' and the reflection coming back as... as a recording of the... the response two or three seconds, whatever it was, later, 'Hello, moon'. And I... I demonstrated this during one of my Reith lectures, which I'll talk about later on, so that's the kind of researches that were going on at Jodrell during the building of the telescope.

Bernard Lovell (1913-2012), British radio astronomer and founder of the Jodrell Bank Observatory, received an OBE in 1946 for his work on radar, and was knighted in 1961 for his contribution to the development of radio astronomy. He obtained a PhD in 1936 at the University of Bristol. His steerable radio telescope, which tracked Sputnik across the sky, is now named the Lovell telescope.

Listeners: Megan Argo Alastair Gunn

Megan Argo is an astronomer at the University of Manchester's Jodrell Bank Observatory researching supernovae and star formation in nearby starburst galaxies. As well as research, she is involved with events in the Observatory's Visitor Centre explaining both astronomy and the history of the Observatory to the public.

Alastair Gunn is an astrophysicist at Jodrell Bank Observatory, University of Manchester. He is responsible for the coordination and execution of international radio astronomical observations at the institute and his professional research concerns the extended atmospheres of highly active binary stars. Alastair has a deep interest and knowledge of the history of radio astronomy in general and of Jodrell Bank in particular. He has written extensively about Jodrell Bank's history.

Tags: the Moon, Faraday effect, Reith lectures, Jodrell Bank, USA, Cyril Hazard, Robert Hanbury Brown, J V Evans

Duration: 7 minutes, 1 second

Date story recorded: January 2007

Date story went live: 05 September 2008