LISTENING TO THE SUN ON SHORTWAVE

New Zealand Listener, Volume 18, Issue 467, 4 June 1948, Page 16

LISTENING TO THE SUN ON SHORTWAVE

THEN Galileo looked through his telescope at the Milky Way he brought the world to the threshold of a new era in scientific discovery and progress, and to-day, as the years pass and existing instruments are improved or new ones brought into being, man’s vision of the universe is still expanding. Astronomers the world over are even now eagerly awaiting the results of the first observations to be made with the giaft 200-inch telescope on Mount Palomar, California. : Not least among recent scientific advances was the employment-dating from the war-of radio and radar as effective instruments for astronomical observation. Many will remember the" mild sensation caused a while ago when American experimenters successfully -made radar contact with the moon, but less is known about the work of a group of Australian scientists who in 1946 first made observations of the sun’s radiation in terms of radio frequencies. Using a micro-wave radio receiver equipped with a special antenna that could be pointed towards the sun, they observed not only the varying micro-wave radiation of the ‘sun, Mut even the disturbance of that radiation. produced by sunspots.. Previously, the connection between the sun and radio had been noticed when magnetic storms (caused by solar flares) interrupted shortwave radio communications through their effect on the ionized layers of the earth’s upper atmosphere, from which radio waves are reflected. Clouds Don‘t Matter At present visiting New Zealand is Dr. C. W. Allen, an Australian solar astronomer who has been working for

some years in this field and who is now on his way to two world conferences being held in Europe next Augustthat ‘of the International Astronomical Union at Zurich, and that of the International Union of Geodesy and Geophysics at Oslo. The Listener met Dr. Allen last week at Wellington’s Carter Observatory. The sky (as in most other parts of New Zealand at the time) was cvercast, and it was raining. "You mightn’t think it’s much of a day for astronomical work," he said, "but cloud doesn’t affect the kind of sun-rays I’m investigating." He told us that although he was a solar astrono-

mer, the particular field in which he was working at the moment was the investigation of "solar noises" by means of radio. "They’re not really noises in the sense that a noise is caused by a pressurewave hitting the ear-drum," he said, "We call this radiation ‘noise’-solar noise if it comes from the sun, or cosmic noise if it comes from the stars generallyto distinguish it from cosmic rays, which are quite angther, thing. We pick up the radiation on a special shortwave re-. ceiver, If you turn the set up high so that it makes a hissing noise’ — he demonstrated what that sounded like"you can hear the solar noise coming through slightly ‘louder. and in_ short bursts’--he demonstrated what they would sound like too. The waves were recorded on instruments and collated in various ways, he added, We asked him what practical use was being made of the information gathered, In the first place, he said, solar noises formed a kind @f extension of the sun’s spectrum. He explained how the sufi’s light is analysed by means of a spectroscope into its constituent colours, or wavelengths, for more detailed study. As different substances had different wavelengths, study of the spectrum revealed the different elements in the sun’s atmosphere-helium was one, for instance. Solar noise was like another colour being added to the spectrum ("like a kind of ultra-ultra-infra-red," he said) and the observation of it should give more information about the physical conditions of the chromosphere (the upper part of the sun’s atmosphere) and the corona, especially of those active features which are not yet fully under-_ stood, "Actually the whole physical picture of the sun’s influence on the earth is not yet fully understood," he said, "but we are learning more all the time." We asked him what he meant by the active features of the sun’s atmosphere about which it was hoped to learn more. Radar Started It "We first got on to solar noise during the war," he explained. "Radar operators noticed that when they pointed their sets towards the sun they got very high noise-level coming through. They also found that this noise-level was extraordinarily variable, and one of the things that we haye since found in observations is that whereas radiation from the sun in the visible spectrum is surprisingly constant, the ‘solar noise’ radia- . tion we get-in the 60-megacycle band anyway-varies enormously, which shows it is a different kind of radiation. Furthermore. this radiation ic associated

with other forms of solar activity such as we observe in sun spots." "Would eclipses help your research?" "Yes. At the eclipse in South America last year observation of solar noise was carried out. The value of the eclipse is that it enables us to localise our source of sound, Normally, you understand, we get solar noise radiations from the sun’s whole mass, but from eclipses we have found that the active (i.e, variable) radiation we get on certain wavelengths seems to come more from the central part of that mass, while the non-active stuff comes from the whole area. Results like these are used to find out®* more about the actual condition of the (continued on next page)

(continued from previous page) sun’s. atmosphere, and consequently about the sun’s influence on the earth. We hope to find out more about such things as shortwave radio conditions and magnetic. disturbances. We may be able to bring about improvements in the forecasting, for years ahead, of critical frequencies for shortwave transmission." North Auckland Experiments We asked him whether the 74-inch telescope being built at Mt. Stromlo, Canberra, would have any effect. on his work. "The effect will probably be to take me out of solar astronomy into stellar astronomy," he said. A party of Australian scientists were coming to. New Zealand soon to study cosmic noise, he went on. They were going to the Leigh headland north of Auckland where they could make use of the. interference that reflected radiation from the sea made with direct cosmic radiation. They hoped in this way to be able to locate more accurately the sources of cosmic noise which seemed to be coming from the constellation Cygnus. The conference which he would attend at Zurich was normally a triennial affair, he said, but owing to the war. none had been held since 1938. All countries were represented, recent ad- vances in astronomy were discussed, terminology stabilised, and so on. He had decided to go to Europe via New Zealand so that he could visit relatives here, he added. The other Australian delegate, Dr. Woolley, had gone via South Africa.