June 1961 - The Amateur Radio Astronomer

Amateur astronomers are common; many of them carry out very useful work. Amateur radio astronomers are much fewer, mainly because the equipment needed is too complex for the non-specialist. Yet, as always, it is the exception that proves the rule - and in this case the 'exception' is Frank. W. Hyde, who has established a full-scale radio astronomy observatory at St Osyth, near Clacton. For the 1961 June programme we decided upon an 'outside broadcast with a mobile television unit, and the programme was actually carried out from the Hyde Observatory at St Osyth.

1960 Local television news item, without sound, of the observatory in St. Osyth owned by the pioneering, amateur radio astronomer, Mr Frank Hyde.

So far as most sciences are concerned, it may safely be said that the day of the amateur is over. The amateur physicist, chemist, or biologist, working with home-made equipment, can hardly hope to make substantial contributions to knowledge. In a few branches, however, the amateur still has a part to play; and this is particu­larly true of astronomy. Observations of the Moon, planets, variable stars and other objects carried out by amateur astrono­mers are still of great value.

One of the newest branches of the science is radio astronomy. This is generally regarded as being purely for professionals. How­ever, such a view is not entirely accurate, for here, too, the enthu­siastic and skilful amateur can fulfil a useful role. In Britain, for instance, there is a full-scale amateur radio astronomy observatory at Clacton, built and operated by F. W. Hyde, which has achieved wide recognition and respect.

Radio astronomy dates from the early nineteen-thirties, when Karl Jansky, in America, was investigating the problems of’ static'. During the course of his experiments he discovered that radio emission was coming from the sky, and he tracked it down to certain regions of the Milky Way. This research was of funda­mental importance, but curiously enough Jansky never followed it up, and his work attracted little attention at the time Shortly before the outbreak of war, another American - an amateur named Grote Reber - began experimenting on his own account. He built a 30-foot parabolic reflector, and, working on frequencies in the region of 150 to 160 Mc/s, not only confirmed Jansky's results but actually produced a chart of the radio sky. It may justly be said that Reber's paraboloid was the first radio telescope deliberately built for such a purpose; it must be remem­bered that Jansky's original detection of radio waves from the Milky Way was not the result of a deliberate search.

It may be as well to add that not all radio telescopes are para­boloids of the type used by Reber, and now world-famous owing to the 250-foot 'dish' at Jodrell Bank. Sometimes a fixed array of aerials will suffice for an investigation; in this case, the 'telescope' will be 'steered' by the rotation of the Earth on its axis. Alterna­tively, a large number of small systems may be grouped together; in other cases a large aerial may be used in a fixed position, together with a small movable aerial. With the Mills Cross, there is an arrangement using two lines of aerials which cross each other. There are in fact many different patterns, each with its own advantages and drawbacks.

To obtain high resolution in radio astronomy, it is necessary to use large aerial receiving systems, which increase in size as the wavelength used becomes longer. It might therefore seem that the size and complexity of such an installation puts radio astronomy beyond the reach of the amateur. This is not the case, and even with comparatively simple apparatus it is possible to carry out radio studies of the Sun. Here, a wide frequency range is available, and the apparatus will consist of a suitable aerial pre-amplifier, a communication receiver, and a tape recorder or (preferably) a pen-recorder.

It is also possible to make use of an ordinary television receiver. After the normal programmes are finished, the background noise received from the aerial becomes visible on the screen, and variations in this background may be observed. If the receiver is tuned to any of the channels between 1 and 3, effects of aurorae may be observed; during a major display shadows will be noticed, sometimes sufficient to break through the picture if official trans­missions are in progress; and at the same time a variable rumbling sound will be evident. With this simple arrangement, the duration and intensity of an auroral display may be checked.

Because radio astronomy involves prolonged periods of observa­tion, the pen-recorder is invaluable; the equipment can therefore be in use even when the operator is not present. Moreover, weather conditions are immaterial, and here the radio astronomer has a tremendous advantage over his optical colleague - to him, clouds do not matter in the least!

Pen-recorders are admittedly expensive, but it is nevertheless possible to make a reliable recorder from Meccano parts; any amateur who has constructed a clock drive for an optical telescope is unlikely to find the task very troublesome. The tape recorder suffers from the disadvantage that it will not run for more than an hour or so without being re-set, but it is naturally much better than nothing at all.

The Hyde radio astronomy observatory at Clacton began, many years ago, in a back garden; a great deal of useful experience was gained, even when a tape-recorder was used in lieu of a pen- recorder. Subsequently it became evident that a special field of interest would be the lower range of the radio spectrum, from frequencies 18 to 35 Mc/s. It was for this reason that the apparatus was moved to some derelict marshes, where more space was available.

Frank Hyde in the control room of the St Osyth Radio Astronomy Observatory.

Aerials were set up, about 1,000 feet apart, with the receiving and recording equipment housed in a caravan. Research on the outer corona of the Sun was undertaken, and proved to be so promising that it was decided to seek a more permanent site for a full-scale observatory. Such a site was found at Beacon Hill, St Osyth. The area covered was six and a half acres at high tide and ten acres at low tide, with 500 feet of private foreshore, and a Martello tower. There was 180 degrees of clear vision optically from east to west, the sea being to the south and east; the few houses nearby were well behind the site of the aerials, and were at lower levels, so eliminating all possible sources of electrical and optical interference. The Martello tower itself was, like others of its kind, built during the Napoleonic Wars; it is 32 feet high and about 140 feet in circumference, with walls 8 to 12 feet thick. During the last war a thick concrete roof was added, and this now provides an ideal platform for the optical telescope erected there.

The first floor of the tower is used as a workshop and store. The top floor has three rooms, one large and two small. One of the small rooms houses the instruments, and is what one may call the 'eye­piece' of the radio telescope. The second small room serves as a library and study, and in the large room the long paper charts may be laid out for comparison with each other.

There are five radio telescopes in operation. Some are of the interferometer type, and work in various combinations with each other; the largest arrays are those of 19 Mc/s, used to study radio emissions widely believed to come from Jupiter. The second largest telescope operates on 27 Mc/s, and has been engaged on studying the extent of the Sun's corona, particularly during the annual occultations of the Crab Nebula. The remaining instru­ments operate at the high-frequency end of the spectrum. One of them works on 440 Mc/s, and is normally used for flare patrol of the Sun. The aerial is mounted on a long pole which can be rotated by means of a hand-winch at the bottom; again the output from this aerial is fed into the instrument room, where the results are recorded by the pen-recorder.

The Crab Nebula is one of the most interesting radio sources in the sky, and since this is an object which has been closely studied at the Hyde Observatory a few further comments about it may be appropriate.

The Nebula is visible in a small optical telescope as a misty patch; photographs taken with large instruments reveal intricate structure. It represents the remains of a supernova observed by Chinese astronomers in the year 1054. (This, incidentally, is one of the very few supernovas seen in our Galaxy in recorded times; the only other cases are Tycho's Star of 1572 and, possibly, Kepler's Star of 1604.)

The Crab Nebula lies in Taurus, and is known in radio astro­nomy as Taurus A, since it was the first discrete source to be identi­fied with an optical object. Its radio spectrum has been carefully studied through a wide frequency range, from 18-3 to 9,400 Mc/s. The spectrum shows an interesting property: the intensity of the radiations does not fall off so rapidly from the low to the high frequencies as is generally found with radio sources. The Nebula seems to be composed of two interpenetrating systems; the rela­tively slender filaments, which form an envelope expanding at the very high velocity of 1,000-1,300 Km/sec., and the centre, a large compact mass almost filling the interior of the Nebula. The distance from us is 3,500 light-years, and we are therefore recording emissions, both optical and radio, which left the Nebula 3,500 years ago.

Owing to the rapid expansion, the diameter has already attained almost 5 light-years - that is to say, over 25 million million miles. The Russian astronomer Shklovsky has suggested that both optical and radio emissions are due to electrons spiralling in a strong magnetic field, and this idea of a 'synchrotron effect' has been supported by the fact that the optical emission has now been found to be partially plane-polarized. The outflow of energy is more than 100,000 times that of the total output of the Sun, and it seems that nuclear reactions must be continuing near the position of the central star.

The Crab Nebula provides us with an important source of radiations which we may use to measure the super-corona of the Sun. Since the radio emission from the solar corona extends out well beyond the edge of the visible corona, some such method is needed, particularly since with increasing distance from the optical Sun the frequencies radiated become lower and lower until they are too low to penetrate our ionosphere. Fortunately, each mid- June the positions of the Sun and the Crab Nebula are sufficiently close to permit observation of the disappearance of the Nebula behind the solar corona. Since the super-corona will affect electro­magnetic radiations, we are able, by means of the reduction of the level of radiations, to determine the density of the super-corona. It has been found that the super-corona extends from ten to fifteen times the diameter of the Sun into the Solar System.

The Sun does indeed offer a fruitful field for the amateur radio astronomer. The range of frequencies emitted is so wide that relatively small aerials and simple receiving equipment will permit useful work; for instance, the correlation of radiations from the quiet Sun compared with those of the active Sun enables valuable statistics to be compiled.

Neither should other sources be neglected. In particular, there is the remarkable object Cassiopeia A, which appears to be located inside our Galaxy. There are indications that the strength is decreasing, but only observations carried out over a long period will enable reliable conclusions to be drawn. The Cambridge workers have assessed the reduction in intensity as being as great as i per cent per year.

Observations at the Hyde Observatory cover a wide range, notably investigations of the Sun and its corona, the plotting of radio sources, and examination of radiations at the low-frequency end of the spectrum to determine the effects of the ionosphere upon them. Also receiving attention is the problem of scintillation. Most people are familiar with optical scintillation or 'twinkling'; a star near the horizon will twinkle violently, whereas a star near the zenith will appear to shine much more steadily. These effects are, of course, due entirely to the Earth's atmosphere, and have nothing to do with the stars themselves. (In general, a planet twinkles less obviously than a star, because it appears as a small disk instead of a point of light.) With a radio source, scintillation takes the form of the varying intensity of signal over a short period, and is due principally to the ionosphere. Studies of this kind are most important, since each extra piece of information makes the picture of our Galaxy and, indeed, the universe itself more complete.

Since 1957 a new branch of radio astronomy has made itself felt.

This is, of course, connected with the earth satellites and planetary probes. Here Britain leads the way, and so far the 250-foot para­boloid at Jodrell Bank holds pride of place. Both radio and radar astronomy are of the utmost importance in all space research work.

Of course, it would be idle to suggest that the amateur radio astronomer can ever rival the professional. Normally, indeed, he will not try to do so, but will concentrate upon routine work to­gether with any special investigations which happen to interest him particularly. There is enormous scope, and it may be that in the years to come the amateur radio astronomer will contribute as much to knowledge as the optical amateur astronomer has done in the past.