February 12 1965 - Balloon Astronomy

In this era of rocket probes and artificial satellites, it may seem a retrograde step to turn back to the humble balloon. Yet as an astronomical vehicle, the balloon has much to recommend it, and it seemed well worth while to devote a programme to balloon astronomy in general.

To an astronomer, the Earth's atmosphere is a source of conti­nual annoyance. It is dirty and unsteady, so that images of celes­tial bodies are always to some extent blurred; to take really long- exposure photographs, of say, the surface of Mars is pointless, since the fine detail will not be registered. From this point of view the Solar System observer is in worse case than the astro­physicist, who is concerned with what are to all intents and pur­poses point sources of light; no star, apart from the Sun, shows a measurable disk even in the largest telescope yet built. However, there are more serious troubles to be faced. The atmosphere is not transparent to radiations of all wavelengths; in a large part of the electromagnetic spectrum it is depressingly opaque, so that astronomical information obtainable at ground-based observa­tories is very incomplete. From this point of view, the practice of setting up large telescopes on high mountains is of little help, though it does improve the clarity of the optical images.

The atmosphere of our world is quite extensive, and traces of it linger on up to at least 2,000 miles above sea-level, but its density falls off rapidly with height. More than 90 per cent of the total air-mass lies below thirteen miles, and more than 99 per cent of the mass below twenty miles; the upper reaches are very tenuous indeed. Unfortunately, the chief blocking-out of radia­tions is due to layers in the ionosphere, that part of the atmosphere which begins at an altitude of forty miles or so. The so-called D. E, Fi and F2 layers range up to more than 100 miles; these are regions where free electrons are found in great numbers, making ±.e levels electrically conducting (and, incidentally, making I ring-range radio communication possible, by bouncing wireless raves of certain frequencies back to earth). The layers are pro­duced by X-rays and ultra-violet rays from the Sun, which act : n the thin air; the X- and many ultra-violet rays are themselves absorbed in the process, so that they do not penetrate to the ground.

Lower down comes the ozone layer, which absorbs most of the remaining solar ultra-violet. If, therefore, we are to study these important radiations, we must send our recording instruments up to great altitudes.

Of course, rockets and artificial satellites can go far above the ionosphere, and even escape from the Earth. Yet they are com­plex and expensive, and in their present stage of development they cannot lift massive telescopes, keep them steady while the :observations are being carried out, and then return them safely. Balloons are much easier to handle, and are also vastly cheaper. Their main limitation is that they are incapable of rising to the ionosphere. A height of between 80,000 and 90,000 feet is as much as can reasonably be expected, and so balloon-borne instruments can contribute little to either ultra-violet astronomy :r X-ray astronomy. All the same, the balloon has much to be said in its favour, since it can at least carry heavy equipment above most of the atmospheric mass - thus eliminating blurring and unsteadiness of the images. Moreover, water-vapour and carbon dioxide in the lower air absorb most of the infra-red radiations sent to us from the planets. Balloon ascents overcome mis hazard with ease.

Hot-air balloons date back to the year 1783, and within a few months of the first flight a French scientist, Charles, went up two miles in a free balloon. Yet there is little resemblance between mese crude vehicles and a modern scientific balloon, which has : y now become an important research tool.

The main development has been carried out by M. Schwarzschild and his team at Princeton University in the United States, in collaboration with the United States Navy, the National Science Foundation, and the National Aeronautics and Space Administration. The 'Statoscope' flights of 1959, concerned mainly with studies of the Sun, were remarkably successful, and the project has now been extended. With Statoscope II, the over­all height from the telescope to the top of the launch balloon is 660 feet; the balloons together weigh over two tons, and another two tons of ballast are carried for later release if height has to be maintained during the night. The telescope, plus its controls, weighs three and a half tons. Two large parachutes are also carried; in case of emergency, the instruments and their records can be separated from the main balloon system, and brought down gently. Many of the radio and electronic devices used are similar to those of artificial satellites.

The launch of such an enormous, fragile system must be under­taken on a calm day, with a wind speed of less than fifteen miles an hour or so, and takes some time. The inflated launch balloon lifts the long, folded main balloon, the twin parachutes, and the telescopes with its associated instruments and controls. Two large lorries are used to cancel out any ground-wind; finally, when the long train of items is extended vertically, the tethering stay is dropped and the whole assembly rises into the upper air at a rate of 800 feet per minute.

During the ascent, helium gas from the launch balloon vents into the main balloon, so that at the chosen 'cruising' altitude (about fifteen miles) the main balloon will be fully inflated. At this point, radio commands direct the telescope towards the objects under study. The telescope locks on to each object in turn, while the observations are made. The procedure is far from simple, but is much more straightforward than with an earth satellite or space-probe; the balloon is what may be termed a 'local' vehicle, and is much more under control. The vital ad­vantage is that the actual instruments and records are recovered, to be examined at leisure and in comfort.

A model of Statoscope II left, and the balloon itself after launch right

The new telescope for Statoscope II would be regarded as very fine even by ground-observatory standards. It is a reflector, with a 36-inch mirror made of fused quartz. The entire telescope unit will be able to point to selected objects in the sky with re­markable precision, and will remain pointing steadily to an accuracy of 1 /50 of second of arc. At peak altitude, where the atmosphere is so thin, the telescope will be capable of detecting fine details on the Sun, Moon, and planets only 1/10 of a second of arc across - which is comparable to using a telescope based in London to see a man who is as far away as New York.

Important discoveries have already been made by balloon- telescope techniques. For instance, detailed photographs of the Sun's surface have been taken, showing features beyond the range of ground telescopes. It has long been known that the solar surface is 'granulated', but the individual granules are compara­tively small, and are in rapid motion, so that they are not easy to study. Balloon photographs show them with amazing clarity, and show that the granules are not of uniform size. The structure of sunspots has also been shown in more detail than ever before.

Stellar astronomy has also benefited, but in view of the present emphasis upon rocket probes it may be worth saying something about the balloon results with regard to Mars and Venus.

Mars, where there is an atmosphere - even though a thin one - has been specially studied, particularly with regard to atmos­pheric water-vapour. There is so little moisture that ground-based instruments were unable to detect it at all; its traces were masked by the water-vapour in our own air. Balloon telescopes have been able to observe from heights where terrestrial water-vapour can b e neglected, and for the first time definite traces of moisture have been found in the Martian atmosphere.

The first serious balloon studies of the second of our 'neighbour' planets, Venus, were made in November 1959, by Ross and Moore in the United States. Until then it had been tacitly assumed that the atmosphere of Venus contained no appreciable water- vapour, and the clouds, whatever they might be, were not made t: H20. The balloon results showed otherwise. Instead of being bone-dry, the atmosphere contained more water-vapour than that of the Earth at an equivalent level. These early results have been substantially confirmed by more recent balloon flights, and it also appears that the clouds are composed of ice crystals. (This does not mean that the planet's surface is likely to be refreshingly cool; Venus is almost certainly very hot indeed.)

So far as balloon astronomy as a whole is concerned, we must admit that it will always be limited in scope; a balloon, by its very nature, has a definite 'ceiling'. For studies which involve going up above the shielding layers in the ionosphere the rocket must remain our only answer. Yet there can be little doubt that balloon techniques have proved their worth, and will be widely used in the future. By space-research standards they are very cheap; the main cost lies in the telescopes and other instruments which are to be lifted - but it is not essential to use giant telescopes. Reflectors of, say, forty to fifty inches aperture probably represent the practicable maximum.

Manned ascents for scientific research have often been made, but generally speaking there is no need to risk human life. The records are obtained photographically, and a visual observer on the spot could not add a great deal, interesting though the ex­perience would be. It is the unmanned, instrument-carrying balloon, operating from altitudes of fifteen miles or so, which will prove of most value in the long run.

Almost all modern work in balloon astronomy has been carried out by the Americans, but since the results are so encouraging it is presumably only a matter of time before the Russians join in ; we may hope, too, for British participation. It is too early to say just what the next developments will be, but we may be sure that the balloon, as an astronomical tool, has come to stay.

April 30 1965 - Astronomy without a Telescope

Many viewers of The Sky at Night had written in to complain that most of the objects discussed were beyond the range of all but the telescope- owner. This, of course, is a perfectly valid criticism; the astronomer would be sadly handicapped without his telescopes. On the other hand, there is a great deal to be seen with the naked eye - when one knows where to look: and, with Henry Brinton, I did my best to point some of these out.

Subsequently, I invited viewers to make drawings of the Full Moon as seen with the naked eye, and send them in. In the next programme we showed several and I was surprised how good they were. Some of them came from schoolboys, who clearly had no access to published lunar map:, and on the whole I am surprised that pre-telescopic era charts of the Moon were not better than they actually were.

An astronomer is always pictured as a man with a large telescope. This is perfectly logical; without telescopes, our knowledge of the universe would be comparatively slight, and modern research has to be undertaken with the aid of very powerful instruments, j Yet there is a great deal of interesting observation open to the enthusiast who has no optical equipment at all, and naked-eye studies are certainly not to be despised.

The first step to be taken by the beginner is to learn the various constellation patterns, which is not nearly as difficult as might be thought. One good scheme is to select a few easily-found group: and then use these as direction-finders to more obscure constella­tions as well as bright stars. The two best 'sky marks' are Orion: and the Great Bear, both of which are prominent in the evening sky during winter, though by spring Orion has more or less disappeared in the evening twilight.

Ursa Major, the Great Bear or Plough, is circumpolar in Britain; that is to say it never sets, and is always to be seen when-1 ever the sky is sufficiently dark and clear. During May evening it is fairly high up, and makes a splendid guide. For instance, the tail of the Bear (or, alternatively, the handle of the Plough) shows the way first to the brilliant orange star Arcturus, in Bootes or the Herdsman, and then to Spica in Virgo, which is less striking "than Arcturus but which is nevertheless very prominent in the south-east. Also to be found from the Bear is Polaris, the Pole Star, which lies within a degree of the north pole of the sky, and which seems to remain almost stationary with the other celestial bodies moving round it.

Polaris is not placed exactly at the pole, as a simple experiment will show. If you take an ordinary camera, point it towards the celestial pole and then give a time exposure, the result will be a series of star-trails. The bright, short trail near the centre is that of Polaris, and the position of the true pole is easy to estimate. Pictures of this sort may be taken with no trouble at all; the only point to remember in aiming the camera is that the altitude of Polaris above the horizon is approximately equal to the observer's latitude on the Earth.

The two 'Pointers' in the Great Bear are named Dubhe and Merak; Dubhe is slightly brighter than the Pole Star, Merak a little fainter. If the line from them is extended in the opposite direction, away from Polaris, it will come to the constellation of Leo (the Lion) marked by a curved line of stars shaped rather like a question-mark twisted the wrong way round. Regulus is the brightest of these stars, which make up the so-called 'Sickle'.

It is often said that a star twinkles, but a planet does not. This is not strictly true, since a planet low on the horizon may twinkle violently, but it is correct to say that a planet twinkles less than a star, because it appears as a tiny disk instead of a mere point of light. Twinkling is due entirely to the effects of the Earth's atmosphere, so that it is most marked with objects low down in the sky.

Superficially one star looks very much like another, but the careful observer will soon notice that the colours are not all the same. Of the three brightest stars in the northern hemisphere of the sky, Arcturus is orange, Capella yellow, and Vega bluish. All three are visible during spring evenings (though Vega is ad­mittedly rather near the horizon), and it is instructive to compare them. Binoculars, of course, will bring out the different colours very well, and will also show various hues among the less brilliant stars; thus Dubhe, the senior of the two Pointers, is decidedly yellower than its companion Merak.

There are also some stars which are double, since they are made up of two components very close together. The best example of a naked-eye double is Mizar, the second star in the tail of the Great Bear, which has a much fainter star, Alcor, close beside it. There is a minor mystery about Alcor, since the old Arab astro­nomers of a thousand years ago stated that it could be seen only under good conditions and by keen-sighted observers. Nowadays this is not the case, and anyone with normal vision can see it whenever the sky is reasonably dark and there is no mist or cloud about. Telescopically Mizar itself is found to consist of two com­ponents, so close together that to the naked eye they appear as one, while one of these components is itself known to be double.

Other naked-eye pairs may be found, notably Nu Draconis in the Dragon's head and Epsilon Lyrae in the small but interesting constellation of Lyra, the Harp. Epsilon Lyra lies close to Vega, and is of special interest because it is a multiple object; each component is again double, so that we have a fine example of a quadruple star. With the naked eye, the appearance is that of two rather faint stars, very close together. Another easy pair L: Theta Tauri, in the Hyades cluster close to the brilliant reddish Aldebaran.

The naked-eye observer can also interest himself in variable stars, which brighten and fade over relatively short periods of a few days or a few months. Betelgeux in Orion is one such case sometimes it is little brighter than Aldebaran, though it has ah: been known to rival the brilliant Rigel. Other variables art Scheat in the Square of Pegasus, Mira in Cetus (the Whale), an: two of the stars in the famous W of Cassiopeia. With all these stars the variations are intrinsic, but things are different with Algol, the 'Demon Star' in Perseus, which seems to shine steadily for two and a half days at a time and then exhibits a long, slow 'wink' lasting for several hours before regaining its normal brilliancy. Strictly speaking, Algol is not variable, but is made up of two stars, one much more luminous than the other, moving round their common centre of gravity; when the fainter star passes in front of the brighter, the total light shows a decrease. With Algol, the whole cycle of changes is easy to follow with the naked eye.

Of the star-clusters, much the most celebrated is that of the Pleiades or Seven Sisters, which is prominent throughout the winter but which sets soon after the Sun by spring.

Normal-sighted persons can see seven separate stars in the group, so that the familiar nick-name is very appropriate. On the other hand, Eduard Heis, a last-century German astronomer, is reputed to have been able to see nineteen Pleiades without optical aid!

The Hyades, round Aldebaran, are brighter than the Pleiades, but are more scattered, so that the effect is not so spectacular. (Incidentally, Aldebaran itself is not a true member of the cluster; it simply happens to lie in much the same line of sight, and is only half as far away from us.) Another naked-eye cluster is Praesepe in Cancer; moonlight will drown it, but on a dark night it is by no means hard to see. It is a fine sight in a telescope, and has earned its unofficial name of’ the Beehive'.

Occasionally a bright nova, or temporary star, will appear in the sky. To be precise, a nova is not a new star; what happens is that a formerly very faint star suffers an outburst which makes it flare into short-lived prominence, though after a brief period of glory it fades back to its former obscurity. The outburst affects only the star's outer layers, so that no lasting damage is done, whereas in the much rarer supernovse the star's material is blown away into space, leaving nothing more than an expanding cloud of gas. Four supernova;, the stars of 1006, 1054, 1572, and 1604, have appeared in our Galaxy since records began; the first of these has left its debris in the form of the Crab Nebula, which is of the greatest interest to both optical and radio astronomers, but which is below naked-eye visibility. On the other hand, bright novae have been seen often enough, and some of them have been discovered by amateurs. There is always a chance that the naked-eye enthusiast will be fortunate enough to detect a nova, though it must be admitted that the chances are heavily against it.

Only three of the outer galaxies are visible without optical aid and two of these, the Nubecula; or Clouds of Magellan, are too far south to be seen in Europe. The third is the Great Spiral in Andromeda, which may be glimpsed as a dim misty speck.

So far as the Solar System is concerned, the naked-eye observer has considerable scope. He can see some of the waterless 'seas' on the face of the Moon, he can make useful observations of meteors and auroras, and he can study the artificial satellites such as the American Echo balloons.

Before the war, our knowledge of meteor paths depended almost entirely upon observations made without a telescope. The procedure was to plot the apparent track of the meteor against the stars, and estimate its magnitude and duration; if the same meteor were seen by another observer some way off the true height and path could be worked out. This sort of work is still useful, though it is only fair to add that radar methods have now been brought into play and yield more accurate results. Sporadic meteors may appear from any direction at any moment, but most of the bright shooting-stars belong to definite showers, so that some periods of the year are more favourable than others. The most consistent shower, that of the Perseids, is visible in early August; anyone who stares up at a clear, dark sky for a few minutes between, say, 28 July and 15 August will be unlucky not to see at least one meteor.

Auroras, on the other hand, are phenomena of the high atmos­phere, though their cause lies in the Sun. During 1963 and 1964 there were few bright displays, because the Sun was going through the quietest phase of its eleven-year cycle, but activity has now begun to increase again, and there should be more frequent aurora: during the next few years. Since the wonderful lights are due to particles sent out from the Sun, and these particles are magnetic, displays of aurora are best seen in high latitudes; a winter night in, say, Iceland or north Norway would be dull without them. Observers in the northern and central parts of Scotland are often able to see brilliant aurorae, though in England the opportunities are much fewer.

By now there are a great many artificial satellites circling the Earth, and a few of them are really bright, appearing as slowly- moving stars creeping across the sky. Most prominent of all are Echo I and Echo II, both American-launched and both of the balloon type; since they are larger than most of the man-made moons, and were deliberately coated with reflective material, they can hardly be over-looked, and predictions for them are given in various periodicals and daily newspapers. Amateurs have done excellent work in checking on the positions of bright artificial satellites. The procedure is to time the moment when the satellite passes between two known stars or else comes to a position which may be plotted easily on the star-chart. (Gases in which a satellite passes right in front of a star are convenient, but surprisingly rare.) The only essential equipment for this sort of work is a reliable stop-watch, together with a really good knowledge of the constellations.

Though the professional astronomer would be more or less helpless without his telescope, any casual watcher can learn much even if he has no optical aid at all. There is endless variety in the night sky, and there are many fascinating objects to be seen by anyone who knows where and when to look for them. One does not need a powerful telescope in order to take a real interest in astronomy.

April 2 1965 - Astronomy and Astrology

Over the years, I have been referred to many times as 'an astrologer'. There are still some people who confuse astrology with astronomy, and after much deliberation we decided to give a programme to the subject, prompted by the fact that at that time three planets {Mars, Uranus and Pluto) were all in the constellation of Leo.

The results were, predictably, somewhat explosive. Letters from in­furiated astrologers poured in; they ranged from organizers of 'colleges' providing 'degrees' in astrology {at a suitable fee, of course) to one earnest viewer who wrote saying that as I appeared on the television screen, my aura was dull yellow and speckled. All I could do in the latter case was to write back assuring the correspondent that I would do my best to have my aura dry-cleaned before the next programme. There were also letters from flying saucer enthusiasts and followers of the Atlantis cult. I spent many hours battling with the deluge of mail, though with regard to the 'colleges' I admit that I merely put them in touch with each other and took no further action.

The most interesting point about it all was that not one of the astrologers offered any answer to the objections I had put forward. And there were, of course, many letters too from people who were glad that I had pointed out the difference between astronomical science and 'what the stars foretell'.

At the present moment Mars is still a prominent feature of the evening sky. Though it is receding from the Earth, it is still much brighter than any of the stars near it, and its strong red colour marks it out at once. During early April binoculars or low-power telescopes show another planet close beside it; this is Uranus, the third of the remote gas-giants, much larger than either Earth or Mars, but so distant that it is never easy to see with the naked eye. A moderate telescope is enough to show its rather dim, greenish disk, though larger instruments are needed to reveal any of its five satellites.

Uranus lies far beyond Mars, and is in fact very much farther from Mars-than we are. The two planets appear close together simply because they happen to lie in more or less the same line of sight. Both are in the constellation of Leo the Lion - and yet this, too, is merely a conventional means of expression, since even the nearest star is immensely more distant than a planet.

The diagram shows what is meant. The main stars of Leo are shown, together with their distances in light-years. (A light-year, or the distance travelled by light in a period of one year, is equal to rather less than six million million miles.) The curved line of stars which includes Regulus, Gamma, and Epsilon is generally nicknamed 'the Sickle'. Mars, at the moment, is only about 75,000,000 miles away - that is to say, less than seven light-minutes!

To say that Mars is 'in' Leo is therefore decidedly misleading. .After all, a sparrow flying at rooftop-height against a background of clouds is not 'in' the clouds.

There is the further point that the stars of Leo are themselves totally unconnected with each other. Epsilon Leonis is over 250 light-years away from Regulus, which is considerably more than the eighty-four light-years separating Regulus and the Sun. The pattern of the constellation is nothing more than a line of sight effect, and if the Solar System lay in a different direction the stars of Leo might well be spread out all over the sky. In fact, a 'con­stellation' is not truly a constellation at all.

Yet these constellation groups, and the apparent positions of the planets in the sky, form the whole basis of the pseudo-science of astrology, which was widely studied in mediaeval times and which is still taken quite seriously in a few countries, notably India. It was claimed that a person's whole character and destiny was influenced by the positions of the Sun, Moon, and planets against the stars at the moment of birth, and an astrological horoscope was regarded as a most important document. Famous scientists of past times were believers in astrology; even Johannes Kepler, who laid down the famous Laws of Planetary Motion, cast horoscopes (though whether he believed in them is another matter), while the great Sir Isaac Newton was most decidedly a mystic. Still earlier, astrology was thought to be just as important as true astronomy.

Originally the Earth was thought to be flat, and to lie at the centre of the universe. The old Greek philosophers realized that the Earth is a globe, but only a few of them were bold enough to suggest that our world might move round the Sun; indeed, it was not until the sixteenth and seventeenth centuries that the idea of a Sun-centred system became firmly established. Astrology, then, is related entirely to the Earth as a centre.

The mediaeval astrologer was a most influential person. He cast horoscopes for kings and princes, he made weighty pro­nouncements, and sometimes he even predicted the approaching end of the world. Comets were regarded as particularly unlucky, but, according to the astrologers, conjunctions of several planets were even worse.

It is natural that the planets - or some of them - should at times appear close together in the sky; as we have seen, Mars and Uranus are at present only a few degrees apart. But when several bright planets met in the same constellation, in 1524, a famous German astrologer named Stoeffler took the opportunity to fore­cast the end of the world, and caused widespread panic; people even went so far as to build boats and arks so as to escape the expected flood. Much more recently, in 1962, five planets were together in the constellation of Gapricornus (the Sea-Goat), and once again the astrologers were much alarmed. In India, parti­cularly, there was great relief when the planets spread out among the constellations once more and the world still survived.

The Sun, Moon, and planets are confined to a certain region of the sky, known as the Zodiac. This is because the orbits of the planets, including the Earth, lie in much the same plane; the inclination is seven degrees for Mercury and less for the remaining planets. There is, however, one exception: Pluto, which is a relatively faint telescopic object, and was not discovered until 1930. (At present it, like Mars and Uranus, will be found in Leo.) The inclination of Pluto's orbit amounts to seventeen degrees, so that it can leave the Zodiac. This is unlikely to worry the astrolo­gers, and in any case the 'signs' of the Zodiac no longer correspond to the actual constellations, since the effects of precession - that is to say, the slight wobbling of the direction of the Earth's axis - have become quite appreciable since classical times. The vernal equinox, or point where the ecliptic cuts the celestial equator, is still known as the First Point of Aries, but by now it has moved out of Aries (the Ram) into the neighbouring constellation of Pisces (the Fishes).

Two of the other planets, Uranus and Neptune, were also unknown to the old astrologers; Uranus was discovered in 1781. Neptune in 1846. If these planets do in fact exert an influence upon human destinies, it would be interesting to learn why the astrologers did not track them down long before the astronomers could do so with their telescopes! There are also the numerous minor planets, or asteroids, which move round the Sun between the orbits of Mars and Jupiter. It is true that they are small in size, but quite a number of them are brighter in our skies than remote Pluto. One of the asteroids, Vesta, is even visible with the naked eye when best placed, whereas Neptune and Pluto, among die 'proper' planets, are always far below naked-eye visibility.

One of the biggest absurdities of astrology lies in the names of die Zodiacal constellations themselves. The familiar groups, such as Leo, Taurus (the Bull) and Gemini (the Twins) are of ancient origin, though it is worth noting that the Chinese and the Egyp­tians used a completely different system. Nobody is quite sure in which country our own constellations were first described. The old Ghaldcean star-gazers may have been responsible; astronomers in the island of Crete have also been suggested. In any case, Ptolemy, last of the great scientists of ancient times, listed forty- eight constellations in his catalogue of the stars. Ptolemy died about a.d. 180; even then, the patterns were very old indeed.

Yet few of the constellations bear the slightest resemblance in outline to the objects after which they are named. It requires considerable imagination to make a bull out of Taurus, a lion out of Leo, or a crab out of Cancer. Moreover, many of the names are mythological; Leo commemorates the Nemaean lion killed by the hero Hercules during his twelve labours. (Hercules is also in the sky, but he is not in the Zodiac, and is much less brilliant than his leonine victim.)

What was evidently done was to draw up arbitrary figures bearing little or no relation to the star-patterns concerned, and then allot names. When this had been done, the astrologers assigned 'characteristics' to the constellations according to the names that had been given. Cancer, the Crab, is said to be a watery sign. Leo, of course, is virile and positive; it is said that the Sun is at its greatest astrological strength when in Leo.

Altogether, the whole procedure seems to be an excellent case of reasoning round in a circle, and it is hard to understand how any thinking person can take it seriously. It is hardly rational to take a collection of totally unrelated stars, make some sort of a figure out of the pattern, give it a name and then claim real significance for it. One can only echo the words of the Duke of Wellington when greeted in the street by a stranger with 'Mr Smith, I believe?' 'Sir - if you believe that, you will believe any­thing.'

Some astrological predictions come true. This is only to be expected; it would be most surprising if they did not, since they cover all sorts of subjects and are usually wrapped up in suitably nebulous language. Now and again some astrologer will achieve a lucky hit, which will be well publicized. The same is true of personal horoscopes, though for every correct statement there are always several which are very wide of the mark.

One typical case may be cited. Not long ago, an astrological magazine forecast the sudden death of President Kennedy, and gave the correct month of the assassination. This prediction was regarded as a convincing justification of astrology - but it must also be related that during the previous three years the same magazine had foretold the death of President de Gaulle, the deposition of General Franco, and the removal of Dr Salazar of Portugal. It is worth noting, too, that in 1938 and 1939 British astrologers were as emphatic as they were unanimous: there would be no war against Nazi Germany.

Only the credulous will believe that line-of-sight effects 0: planets and stars will have any effect upon a man's character or life, but it is nevertheless illuminating to ask a serious astrologer just how these alleged influences occur. I did ask precisely this question of an astrologer a few months ago. His reply was: hasn’t the slightest idea.' This was, at least, a straightforward admission, and differed from the usual attitude. Most astrologer; faced with such a query, would have started talking about mysticism, ancient teachings, and, of course, vibrations. The latter word is a favourite of all devotees of what may be termed the 'fringe' of science; it is also very convenient, because in such a context it may be taken to mean practically anything.

Arguments which have no basis of common sense are always hard to refute. It is so with astrology, which lacks any scientific or logical foundation, and which is a relic of the past, when super­stition was rife and concrete knowledge was very limited. In ancient times, when the nature of the universe was not under­stood, it was natural enough to regard the Earth as of supreme importance, with the remaining bodies set in the sky merely for the sake of Earthmen; in such a climate, astrology could be ex­pected to flourish. By now it has, of course, been completely dis­credited in Europe, though in the East it lingers on.

It is, after all, virtually harmless, and many people are amused to read the 'What the stars foretell' columns in the popular press. It must also be emphasized that professional and amateur astrologers are, in general, completely honest and sincere. They take themselves most seriously; they give each other 'degrees', they put impressive-looking letters after their names, and they offer instruction to the unenlighted, all with the best of intentions. The same can be said of other equally sincere bodies, such as the International Flat Earth Society, which still exists, and the Ger­man Society for Geophysical Research, whose members be­lieve the world to be the inside of a hollow globe, with the Sun in the centre of the hollow and Australia situated somewhere above our heads.

There seems no need to say more. Astrology is not a science, and no person with any scientific background will take it seriously, but its name still leads to a certain amount of confusion. Suffice it to say that astrology and true astronomy are entirely different, and entirely unassociated. Yet the sincere astrologer does little damage, and, like the flat earther and the hollow-globe believer, he means well.

June 25 1965 - Space Weather

It was in the summer of 1965 that the U.S. probe Mariner IV by-passed Mars and sent back photographs showing that the planet's surface is covered with lunar-type craters. When I presented the July programme, with K. H. Fea, the information was still coming through, but there were other topics also; both Mariner IV and the unsuccessful Soviet Mars probe Zond II had sent back information about the conditions prevailing in the space between Mars and the Earth. The term 'space weather' is by no means inappropriate, and we decided to devote the programme to it. I have left the article as it appeared at that time; up to mid-ig6y no further Mars probes were dispatched, though doubtless there will be more in the near future.

Astronomers all over the world are now busy studying the first close-range photographs of Mars, taken with the American space- probe Mariner IV. A full analysis will take some time, but at least it is now clear that the experiment has been a real success. There are grounds for suggesting that it is the greatest triumph yet in the field of space research.

The photographs are much less spectacular than those ob­tained some months ago when the Ranger craft hit the Moon after sending back highly detailed pictures of the lunar surface. However, Mars is a much more remote target; at the time of Mariner's closest approach to the planet, the distance between Mars and the Earth was in the region of 135,000,000 miles. To keep in touch with the probe across this range was in itself a major feat, and one which proved to be too difficult for the Russians, who have lost all contact with their own Mars rocket, Zond II.

It is not likely that the information obtained from Mariner will solve all the problems of Mars, but it should give us a better idea about conditions on the planet. It must, however, be remem­bered that in addition to photographing Mars, the probe’ has also told us a great deal about the space region between Mars and the Earth. We know more about the 'space weather' of this part of the Solar System than we could even have guessed a few months ago.

The term 'space weather', originally coined by an American scientist, is not so inappropriate as might be imagined. It should not be taken too literally, since there is no weather, in the accepted sense of the word, above the Earth's atmosphere. All normal clouds, for instance, are included in the bottom seven miles of atmosphere, known as the troposphere; higher up come the more rarefied layers, and the atmospheric mantle has no definite boundary, but it is a good approximation to say that the 'air: ends at about 1,000 miles above sea-level. (Incidentally, the fact that the atmosphere is of limited extent has been realized for a long time, and the Arab astronomers of many centuries ago were well aware of it.)

Beyond the atmosphere lies 'space', but we have come a long way from the time when space was supposed to be completely empty. It is now held that there is no such thing as empty space anywhere in the observable universe, though the material is very rarefied by everyday standards.

First, there are countless meteoritic particles in the Solar System, ranging from large blocks down to tiny objects smaller than specks of dust. Large meteorites, weighing more than a few pounds, are relatively rare, and seem to be close relations of the minor planets or asteroids. Meteors which produce the spectacu­lar shooting-star effects are much smaller, and are inferior in size to grains of sand, so that they are destroyed in the Earth'; upper air; there should be plenty of meteors on view during the first fortnight of August, when the Earth passes through the rich and consistent Perseids. Still smaller is the micro-meteoroid; which has too little mass to produce luminous effects when they enter the Earth's atmosphere.

The meteoroid hazard was one of the early bugbears of space­flight, and as recently as the early nineteen-fifties it was still claimed, by some authorities, that a probe venturing beyond the shield provided by the Earth's atmosphere would be promptly battered to pieces by a sort of cosmical bombardment. Luckily, this fear has proved to be ill-founded, because the larger bodies are relatively so rare, and the micro-meteoroids have too little penetrating power to be really dangerous. If interplanetary travel becomes common-place during the centuries to come, there may well be occasional disasters; but if meteoroids were the only hazard, a flight from the Earth to the Moon would be much less risky than a weekend drive from London to Margate!

Mariner IV has been recording micro-meteoroid hits through­out its journey, and there seems to be an increase in strike fre­quency near the Martian orbit, but this was not unexpected. Information has also been provided by the now-lost probe Zond II.

As well as solid particles of this sort, space also contains atoms of gas moving at more than 1,000 kilometres per second. These atoms make up what is known as the solar wind, entirely un­known before space research became a powerful tool in the hands of astronomers. Generally, the solar wind is made up of a steady flow of atomic particles streaming away from the Sun in all direc­tions; the density is so low that a space-probe would find only about ten atoms in every cubic centimetre, but when vast dis­turbances are taking place on the Sun the density increases - or, to put it more graphically, the solar wind becomes gusty. When the denser parts reach the Earth, they upset the magnetic field, as well as interfering with long-distance radio and cable com­munications, and producing spectacular displays of polar lights or auroras.

The brilliant surface of the Sun is known as the photosphere, and is at a temperature of about 6,000 degrees Centigrade. It is composed of gas, and upon it may be seen darker patches, known as sunspots. The spots are at a temperature of 4,000 degrees, and are in fact highly luminous, appearing dark only by contrast against the still more dazzling background. They are not permanent; smaller ones persist for only a few hours or days, while it is rare for even a large spot to last for as much as three months.

The Sun is in some respects a variable star, and exhibits a semi-regular cycle of activity. Every eleven years or so, activity is at its peak; spots are common, some of them showing violent, short-lived outbursts known as flares. The last maximum, which of 1957-58, was the most energetic on record, but recently the Sun's activity has been at a low ebb, and there have been long periods when no spots have been seen. It appears that minimum took place during the winter of 1964-65, and by now activity is starting to build up again; the next maximum may be expected about 1969-70.

When the Sun is active, the solar wind is 'gusty'. It originates not at the photosphere, but in the outer parts of the solar atmos­phere, known as the corona, in a region about 1,000,000 kilo­metres above the brilliant surface. Here the gas particles, mainly the nuclei of hydrogen and helium atoms, are in violent motion, and the temperature is about 1,000,000 degrees. Some areas are even hotter (for reasons not yet properly understood), and it ii thought that these areas are the sources of denser streams in the solar wind.

It is worth noting that the scientific definition of 'tempera­ture' is not the same as the everyday understanding of 'heat". Temperature depends upon the speeds at which the various atomic particles are moving about; the greater the speeds, the higher the temperature. In the solar corona, the temperatures are; colossal, but the material is rarefied, so that the actual heat is much less than in the photosphere. There is something to be gained by comparing a Guy Fawkes' hand-sparkler with are ordinary match. Each spark of the firework is white-hot, but: contains so little mass that the sparkler may be safely held in the hand - whereas to put one's finger into a match-flame is apt: be a painful process, though the temperature of the flame _ lower.

Flares, usually - though not invariably - associated with large sunspots, are sources of radiations and particles. The particles cover the 93, 000, 000-mile gap between Sun and Earth in little over one day, and cause major disturbances in the Earth's mag­netic field. They also produce auroras, known more commonly as Northern and Southern Lights because they are most common and most brilliant in the polar zones. Spectacular displays in England are infrequent, and are to be expected only when the Sun is near the peak of its cycle; from Scotland, aurora are much more usual, and a winter night in, say, Iceland or Northern Norway would seem strange without them. Occasionally, aurora reach as far south as Italy, and there is a story - almost certainly true - that the Roman Emperor Tiberius once dispatched rescue teams because he mistook a bright aurora for a disastrous fire. The Southern Lights are superb in Antarctica.

Aurora: occur in the upper atmosphere, and are caused when the atoms ejected from the Sun plunge into the higher layers. Analysis of auroral light shows that these atoms - or, more accurately, nuclei of hydrogen atoms - are moving down to the ground at velocities of as much as 5,000 kilometres per second. Aurora are mainly confined to the polar regions simply because the Earth has a magnetic field surrounding it in space, and this field channels the electrically charged atomic particles into the regions near the magnetic poles, so that the original paths of the solar-wind particles are markedly altered. The geographical North and South Poles have nothing directly to do with this; it is the magnetic poles which matter.

Some of the particles are trapped in the Earth's magnetic field, at distances up to about 100,000 kilometres from the ground. These particles are enormously accelerated, by processes not yet well understood, and 'bounce' between the Polar Regions in spiralling and drifting orbits. These regions of trapped particles were completely unknown until 1958, when they were discovered by one of the early American artificial satellites, Explorer I. They have been named the Van Allen Belts, in honour of the U.S. scientist James van Allen, who was mainly responsible for their detection. The lower layers may be the by-products of cosmic rays, but the upper layers are closely connected with the solar wind, varying according to the prevailing 'space weather'.

Some authorities believe that aurora: are caused by clouds in the solar wind which strike the outer part of the Earth's magnetic field and send down a form of shock-wave, so that some of the trapped particles are shaken out of their stable orbits and cascade into the atmosphere near the magnetic poles, rather in the man­ner of apples shaken out of a tree. On another interpretation, the particles making up the auroras are never truly trapped at all, but are deviated briefly in a complex fashion. The whole matter is now being intensively studied, but at any rate it is clear that aurora are not so simple and straightforward as used to be thought.

Little positive information about space weather could be ob­tained before the opening of the space age, in 1957, but progress since then has been amazingly rapid. The artificial satellites could provide considerable data, and many vehicles have been launched specially for the purpose. Recently, for instance, there has been another satellite of the so-called 'Imp' series; it has an eccentric orbit, so that it moves partly within the Earth's magne­tic field and partly in the relatively remote regions of undisturbed solar wind. Also important have been the Injun satellites con­structed at Iowa University, whose main function is to study the trapped and cascading particles in the Van Allen layers.

On a longer-term basis, the discovery of the Van Allen layers seems to have hammered yet another nail into the coffin of the elaborate, manned space-station proposed earlier by Wernher von Braun and other pioneers. There are sound reasons for sup­posing that a prolonged stay in the main layers would be inadvi­sable, and the whole idea of a manned base, orbiting the Earth at a height of about 1,000 miles, seems to have fallen into dis­favour, though it would be unwise to say that it has been aban­doned.

The interplanetary probes have added to our knowledge about space weather in general, and the solar wind in general. Much was gained from Mariner II, which passed within 21,000 miles of the planet Venus in December 1962. The Sun's own magnetic field was studied, and seems to vary according to the state of the solar cycle, so that there are significant differences between the findings of Mariner II and the present Mariner IV. Apparently, when the Sun is active its magnetic field is 'pushed outwards' by the solar wind. During the past few months, when Mariner IV has been on its way, the Sun has been at its least active, so that its magnetic field has reached closer in. Rather fortunately, there was a major flare on the Sun on 5 February 1965, and its effects were recorded by Mariner IV; radiation levels increased by 50 per cent, and two days later the probe detected irregular mag­netic fields in space.

One further piece of information is that Mars has no magnetic field comparable in strength with that of the Earth. This means that it can have no Van Allen-type layers either, and the whole situation there is different. It may even be that dangerous radia­tions can penetrate to the Martian surface, which will make matters much more difficult for future pioneers. However, an immense amount of work remains to be done, and every new development means that the study of space weather becomes more and more complex.

June 4 1965 - Spinning Worlds

It seems that every celestial object is rotating, even if the speeds of spin are not the same. The programme of June ig6j was prompted by the announcement that Mercury, the closest planet to the Sun, has not, after all, a 'day equal to its 'year', as had always been thought. This has been confirmed since; and neither is there any reason to question the very long rotation period of Venus, though it is possible that in neither case has the last word been said.

The planet Mercury is one of the less prominent members of the Sun's family. It is never a brilliant naked-eye object, since it can never be seen against a dark background; its distance from the Sun is only 36,000,000 miles, so that it may be seen only for a brief period after sunset or before sunrise low down over the horizon. This year the best opportunity will be during the firs: week in September, when Mercury will be a morning star.

Mercury's sidereal period (that is to say, the time taken to complete one revolution round the Sun) is eighty-eight Earth- days. It has long been supposed that this must also be the time taken for the planet to spin once on its axis, in which case 'the 'day' would be equal to the 'year'. The result would be that: Mercury would keep the same face to the Sun all the time, with part of the surface in permanent daylight and another pan plunged into never-ending night. Between these two extremes, there would be a so-called twilight zone over which the Sun would pass above and below the horizon.

Shown on the left, this is not our Moon, but a newly released mosaic (2011) of the planet Mercury as seen in images from Nasa's Messenger probe.

Behaviour of this sort is known as a 'captured1 rotation', and would mean that the ordinary day-and-night conditions as we know them on Earth would not occur. However, new method: of investigation have now been applied by scientists at Puerto Rico, using the radar equipment at Arecibo. Radar echoes were; obtained from Mercury, and have led to the surprising conclusion; that the rotation period is not, after all, the same as the planet's eighty-eight-day 'year'. The true period seems to be only 58 days.

Consequently, all our ideas about Mercury must be revised. There is no area of constant sunlight, no region of permanent darkness, and no twilight zone; the whole planet experiences a regular alternation of day and night. Yet Mercury is an unwel­coming sort of world, mainly because it has little or no atmosphere and the temperature range is very great. Unfortunately our maps of its surface features are rough, because the markings are diffi­cult to study even with large telescopes. Mercury is a mere 2,900 miles in diameter, and never comes much within 50,000,000 miles of us.

In size Mercury is comparable with our Moon (diameter 2,160 miles), while the second planet outward from the Sun, Venus, is almost the same size as the Earth. There have even been suggestions that Mercury is nothing more than an ex- satellite of Venus which broke free for some reason or other and moved off in an independent path, though such a theory will be extremely hard to prove.

The Moon provides an excellent example of a world with a captured rotation. It travels round the Earth once in just over twenty-seven days, and takes the same time to rotate on its axis, so that it keeps the same face to us all the time, and the surface markings appear fixed. Some of these markings may be seen with the naked eye, and it is possible to draw up rough charts without the use of any optical aid. In response to a request in the April Sky at Night programme, various naked-eye drawings of the Moon were sent in, two of which showed the pattern of dark, waterless seas, notably the well-marked Mare Crisium. In view of these and other similar drawings, it is rather curious that ancient astronomers of pre-telescopic days drew up lunar charts which were not even approximately accurate.

From Earth it is possible to study 59 per cent of the Moon's surface, because of effects known as liberations. Though the Moon rotates on its axis at a constant speed, its velocity in orbit is slightly variable, because its path round the Earth is an ellipse instead of a circle; it moves fastest when closest to us. Consequently, the amount of rotation becomes 'out of step' with the position of the Moon in its orbit, and we can see first some distance round the eastern side, then some distance round the western. The remaining 41 per cent of the surface is permanently averted, and remained unknown until the Russians obtained photographs of much of it with their rocket Lunik III in October 1959.

There is no mystery about this behaviour, and there can be no doubt that tidal friction over the ages is responsible for it. Some thousands of millions of years ago it may well be that the Moor rotated much faster than it does now, and we may assume that: it was then in a viscous or semi-solid condition. The Earth raise huge tides in it, and so slowed down the Moon's rate of spin until relative to Earth, the rotation had stopped altogether. Note, however, that the Moon does not keep the same face towards the Sun, so that day and night conditions on the averted hemisphere are the same as on the hemisphere facing us. A lunar day lasts for almost a month instead of only twenty-four hours.

With Venus, the situation is uncertain. There are no permanent surface markings to guide us, since Venus is concealed beneath its obscuring atmosphere, and before the era of space-probes i: was generally thought that the rotation period must be in the order of a month. Since the planet's 'year' is equal to aimer I 225 Earth-days, there would therefore be only seven or eight: I Venus days in every Venus year.

This idea was challenged in late 1963, when the American vehicle Mariner II passed within range of Venus and sent ban information to the effect that the rotation period was very lour indeed — perhaps even longer than 225 days. Radar work 21 Arecibo by R. B. Dyce and G. H. Pettengill, who have beer responsible also for the new studies of Mercury, gives the period of Venus as 247 days, so that we have a planet upon which tit day is longer than the year! This would mean that to an observer – on the surface, the Sun would rise in the west and set in the east; 10 days later. (In point of fact, seeing the Sun would be very difficult, owing to the cloudiness of the atmosphere. Mariner II gave the surface temperature as around 8oo°F., much too hot for any life to survive unprotected there.)

It would be idle to pretend that all astronomers are satisfied with this picture, but again we must await the results of further work, carried out probably by means of space-probes. When we come to Mars, the first planet beyond the Earth's orbit, we are on much firmer ground. There are visible surface markings, which are carried across the disk by virtue of the planet's rotation, and it is not hard to measure the rotation period, which proves to be twenty-four hours thirty-seven minutes. Mars, at least, has a day which is not very different from our own, and the seasons are also of the same type, since the axis is tilted at about twenty- five degrees as compared with the twenty-three and a half degrees of Earth. The main difference is that the seasons are much longer, since the Martian year is equal to 687 Earth-days.

Jupiter, first of the giant planets, is entirely different. It has a diameter of 88,700 miles as measured through the equator, but only 83,800 miles as measured through the poles, so that it is obviously flattened. This flattening may be seen with a small telescope when Jupiter is on view. Again there is no mystery; Jupiter is gaseous, at least in its outer layers, and the flattening is due to its rapid rotation. The Jovian day is less than ten hours long, so that particles at the planet's equator are being whirled round at some 28,000 miles an hour, and the effects of centri­fugal force cause the equatorial region to bulge out. There is a similar effect for the Earth, but with our world the difference between the polar and equatorial diameters is only about twenty- seven miles, as against 5,000 miles for Jupiter.

Different zones of Jupiter rotate at somewhat different speeds; the period for the equator is five minutes shorter than for the rest of the planet, while definite features, such as the famous Great Red Spot, have periods of their own, though all the values lie between nine hours fifty minutes and less than ten hours. It is also worth noting that the tilt of the axis is only three degrees from the vertical, so that there are no terrestrial-type seasons. In any case, seasons would be of minor importance on Jupiter, where the year is almost twelve times as long as ours, and where the temperature never rises above - 200°F.

Jupiter has four large satellites, again providing us with ex­amples of captured rotation, since all keep the same hemisphere turned towards their huge primary planet. This is also the case with the satellites of Saturn, and, indeed, with all major satellites in the Solar System. Saturn itself is of the same general type as Jupiter, with a gaseous surface and a relatively quick rotation of only ten and quarter hours for the equatorial zone; here, too the globe is markedly flattened.

Beyond Saturn lies Uranus, discovered by Herschel in 1781. At present it lies in the constellation Leo, and earlier in the year appeared close to Mars, but it is not easy to see without a tele­scope, and large instruments are needed to show any detail upon its pale, somewhat greenish disk. It is a giant world 29,300 miles in diameter, with a year eighty-four times as long as ours.

With regard to rotation, Uranus is a celestial oddity. The period is conventional enough for a giant planet (ten and three- quarter hours), but the axial tilt is not. The axis is inclined a: ninety-eight degrees, or more than a right angle, so that the rotation is technically retrograde, and the Uranian seasons are most peculiar. From Earth, we see sometimes the pole, sometimes the equator in the centre of the disk. The reason for this remark­able attitude is unknown, and Neptune, the last of the giants does not have a similar tilt; the angle is twenty-nine degrees, much the same as that of the Earth, while the Neptunian day amounts to about fourteen hours. Accurate data for Neptune are not easy to obtain, since there are no surface features defiant enough to be used as 'markers', and indirect methods have to be employed.

The boundary of the planetary system is the orbit of Pluto, a strange body discovered in 1930 and too faint to be seen in small telescopes. Even its diameter is uncertain, since it appears as little more than a star like point, though recent studies indicate that it may be as large or larger than the Earth instead of a smaller world such as Mercury or Mars.

At the Lowell Observatory in Arizona, where Pluto was first identified, M. F. Walker and R. Hardie have studied the slight variations in magnitude, and have found a period of six days nine hours. This, presumably, must be the rotation period of Pluto; the 'year' is known accurately, and is 2481 times as long as that of the Earth. The method of light-variations has also been applied to the minor planets, or asteroids, most of which keep to a well- defined zone between the orbits of Mars and Jupiter, and periods of a few hours seem to be the general rule. Vesta, the bright­est of the asteroids, has a rotation period of ten and a half, hours.

It is not only the planets and satellites which spin; in fact, rotation seems to be an invariable characteristic of all celestial bodies. The Sun's period may be measured easily enough by the positions of the sunspots, which are carried across the disk from day to day; here, the period amounts to about three and a half weeks, though different zones have different rates of movement. (Sunspots have been rare of late, since we have been passing through the minimum of the eleven-year solar cycle, but activity may now be expected to increase rapidly towards the next maxi­mum.) And spectroscopic work shows that the other stars also rotate, some of them with surprising speed. Even the Galaxy in which we live is in a state of rotation round its nucleus; the Sun takes about 225,000,000 million years to complete one journey, a period which has been graphically termed the 'cosmic year'.

The lesson to be learned from all this is that we must not attri­bute any real significance to a 365-day 'year' and a twenty-four hour 'day'. These periods apply only to our Earth, which is of no importance whatsoever in the universe as a whole. If we lived elsewhere, our time-standards would be quite different, since every celestial body has a rotation period peculiarly its own.

Note added in proof. In 1967 two more Venus probes were successfully sent to the planet, one of which (Venus IV. from Russia) landed there, while the other (Mariner V) by-passec Venus and repeated the Mariner II experiments with much greater precision. The results of these probes, together with radar measures from Earth, give a retrograde rotation period of 243 days and a surface temperature of at least 500 degrees F.; not perhaps so hot as Mariner II indicated, but still hot by Earth/- standards. The planet's atmosphere appears to be very dense indeed. Russian measures give the ground pressure as 15 to 2; times as great as that of the Earth's air at sea-level.

April 30 1965 - Astronomy without a Telescope

Many viewers of The Sky at Night had written in to complain that most of the objects discussed were beyond the range of all but the telescope- owner. This, of course, is a perfectly valid criticism; the astronomer would be sadly handicapped without his telescopes. On the other hand, there is a great deal to be seen with the naked eye - when one knows where to look: and, with Henry Brinton, I did my best to point some of these out.

Subsequently, I invited viewers to make drawings of the Full Moon as seen with the naked eye, and send them in. In the next programme we showed several and I was surprised how good they were. Some of them came from schoolboys, who clearly had no access to published lunar map:, and on the whole I am surprised that pre-telescopic era charts of the Moon were not better than they actually were.

An astronomer is always pictured as a man with a large telescope. This is perfectly logical; without telescopes, our knowledge of the universe would be comparatively slight, and modern research has to be undertaken with the aid of very powerful instruments, j Yet there is a great deal of interesting observation open to the enthusiast who has no optical equipment at all, and naked-eye studies are certainly not to be despised.

The first step to be taken by the beginner is to learn the various constellation patterns, which is not nearly as difficult as might be thought. One good scheme is to select a few easily-found group: and then use these as direction-finders to more obscure constella­tions as well as bright stars. The two best 'sky marks' are Orion: and the Great Bear, both of which are prominent in the evening sky during winter, though by spring Orion has more or less disappeared in the evening twilight.

Ursa Major, the Great Bear or Plough, is circumpolar in Britain; that is to say it never sets, and is always to be seen when-1 ever the sky is sufficiently dark and clear. During May evening it is fairly high up, and makes a splendid guide. For instance, the tail of the Bear (or, alternatively, the handle of the Plough) shows the way first to the brilliant orange star Arcturus, in Bootes or the Herdsman, and then to Spica in Virgo, which is less striking "than Arcturus but which is nevertheless very prominent in the south-east. Also to be found from the Bear is Polaris, the Pole Star, which lies within a degree of the north pole of the sky, and which seems to remain almost stationary with the other celestial bodies moving round it.

Polaris is not placed exactly at the pole, as a simple experiment will show. If you take an ordinary camera, point it towards the celestial pole and then give a time exposure, the result will be a series of star-trails. The bright, short trail near the centre is that of Polaris, and the position of the true pole is easy to estimate. Pictures of this sort may be taken with no trouble at all; the only point to remember in aiming the camera is that the altitude of Polaris above the horizon is approximately equal to the observer's latitude on the Earth.

The two 'Pointers' in the Great Bear are named Dubhe and Merak; Dubhe is slightly brighter than the Pole Star, Merak a little fainter. If the line from them is extended in the opposite direction, away from Polaris, it will come to the constellation of Leo (the Lion) marked by a curved line of stars shaped rather like a question-mark twisted the wrong way round. Regulus is the brightest of these stars, which make up the so-called 'Sickle'.

It is often said that a star twinkles, but a planet does not. This is not strictly true, since a planet low on the horizon may twinkle violently, but it is correct to say that a planet twinkles less than a star, because it appears as a tiny disk instead of a mere point of light. Twinkling is due entirely to the effects of the Earth's atmosphere, so that it is most marked with objects low down in the sky.

Superficially one star looks very much like another, but the careful observer will soon notice that the colours are not all the same. Of the three brightest stars in the northern hemisphere of the sky, Arcturus is orange, Capella yellow, and Vega bluish. All three are visible during spring evenings (though Vega is ad­mittedly rather near the horizon), and it is instructive to compare them. Binoculars, of course, will bring out the different colours very well, and will also show various hues among the less brilliant stars; thus Dubhe, the senior of the two Pointers, is decidedly yellower than its companion Merak.

There are also some stars which are double, since they are made up of two components very close together. The best example of a naked-eye double is Mizar, the second star in the tail of the Great Bear, which has a much fainter star, Alcor, close beside it. There is a minor mystery about Alcor, since the old Arab astro­nomers of a thousand years ago stated that it could be seen only under good conditions and by keen-sighted observers. Nowadays this is not the case, and anyone with normal vision can see it whenever the sky is reasonably dark and there is no mist or cloud about. Telescopically Mizar itself is found to consist of two com­ponents, so close together that to the naked eye they appear as one, while one of these components is itself known to be double.

Other naked-eye pairs may be found, notably Nu Draconis in the Dragon's head and Epsilon Lyrae in the small but interesting constellation of Lyra, the Harp. Epsilon Lyra lies close to Vega, and is of special interest because it is a multiple object; each component is again double, so that we have a fine example of a quadruple star. With the naked eye, the appearance is that of two rather faint stars, very close together. Another easy pair L: Theta Tauri, in the Hyades cluster close to the brilliant reddish Aldebaran.

The naked-eye observer can also interest himself in variable stars, which brighten and fade over relatively short periods of a few days or a few months. Betelgeux in Orion is one such case sometimes it is little brighter than Aldebaran, though it has ah: been known to rival the brilliant Rigel. Other variables art Scheat in the Square of Pegasus, Mira in Cetus (the Whale), an: two of the stars in the famous W of Cassiopeia. With all these stars the variations are intrinsic, but things are different with Algol, the 'Demon Star' in Perseus, which seems to shine steadily for two and a half days at a time and then exhibits a long, slow 'wink' lasting for several hours before regaining its normal brilliancy. Strictly speaking, Algol is not variable, but is made up of two stars, one much more luminous than the other, moving round their common centre of gravity; when the fainter star passes in front of the brighter, the total light shows a decrease. With Algol, the whole cycle of changes is easy to follow with the naked eye.

Of the star-clusters, much the most celebrated is that of the Pleiades or Seven Sisters, which is prominent throughout the winter but which sets soon after the Sun by spring.

Normal-sighted persons can see seven separate stars in the group, so that the familiar nick-name is very appropriate. On the other hand, Eduard Heis, a last-century German astronomer, is reputed to have been able to see nineteen Pleiades without optical aid!

The Hyades, round Aldebaran, are brighter than the Pleiades, but are more scattered, so that the effect is not so spectacular. (Incidentally, Aldebaran itself is not a true member of the cluster; it simply happens to lie in much the same line of sight, and is only half as far away from us.) Another naked-eye cluster is Praesepe in Cancer; moonlight will drown it, but on a dark night it is by no means hard to see. It is a fine sight in a telescope, and has earned its unofficial name of’ the Beehive'.

Occasionally a bright nova, or temporary star, will appear in the sky. To be precise, a nova is not a new star; what happens is that a formerly very faint star suffers an outburst which makes it flare into short-lived prominence, though after a brief period of glory it fades back to its former obscurity. The outburst affects only the star's outer layers, so that no lasting damage is done, whereas in the much rarer supernovse the star's material is blown away into space, leaving nothing more than an expanding cloud of gas. Four supernova;, the stars of 1006, 1054, 1572, and 1604, have appeared in our Galaxy since records began; the first of these has left its debris in the form of the Crab Nebula, which is of the greatest interest to both optical and radio astronomers, but which is below naked-eye visibility. On the other hand, bright novae have been seen often enough, and some of them have been discovered by amateurs. There is always a chance that the naked-eye enthusiast will be fortunate enough to detect a nova, though it must be admitted that the chances are heavily against it.

Only three of the outer galaxies are visible without optical aid and two of these, the Nubecula; or Clouds of Magellan, are too far south to be seen in Europe. The third is the Great Spiral in Andromeda, which may be glimpsed as a dim misty speck.

So far as the Solar System is concerned, the naked-eye observer has considerable scope. He can see some of the waterless 'seas' on the face of the Moon, he can make useful observations of meteors and auroras, and he can study the artificial satellites such as the American Echo balloons.

Before the war, our knowledge of meteor paths depended almost entirely upon observations made without a telescope. The procedure was to plot the apparent track of the meteor against the stars, and estimate its magnitude and duration; if the same meteor were seen by another observer some way off the true height and path could be worked out. This sort of work is still useful, though it is only fair to add that radar methods have now been brought into play and yield more accurate results. Sporadic meteors may appear from any direction at any moment, but most of the bright shooting-stars belong to definite showers, so that some periods of the year are more favourable than others. The most consistent shower, that of the Perseids, is visible in early August; anyone who stares up at a clear, dark sky for a few minutes between, say, 28 July and 15 August will be unlucky not to see at least one meteor.

Auroras, on the other hand, are phenomena of the high atmos­phere, though their cause lies in the Sun. During 1963 and 1964 there were few bright displays, because the Sun was going through the quietest phase of its eleven-year cycle, but activity has now begun to increase again, and there should be more frequent aurora: during the next few years. Since the wonderful lights are due to particles sent out from the Sun, and these particles are magnetic, displays of aurora are best seen in high latitudes; a winter night in, say, Iceland or north Norway would be dull without them. Observers in the northern and central parts of Scotland are often able to see brilliant aurorae, though in England the opportunities are much fewer.

By now there are a great many artificial satellites circling the Earth, and a few of them are really bright, appearing as slowly- moving stars creeping across the sky. Most prominent of all are Echo I and Echo II, both American-launched and both of the balloon type; since they are larger than most of the man-made moons, and were deliberately coated with reflective material, they can hardly be over-looked, and predictions for them are given in various periodicals and daily newspapers. Amateurs have done excellent work in checking on the positions of bright artificial satellites. The procedure is to time the moment when the satellite passes between two known stars or else comes to a position which may be plotted easily on the star-chart. (Gases in which a satellite passes right in front of a star are convenient, but surprisingly rare.) The only essential equipment for this sort of work is a reliable stop-watch, together with a really good knowledge of the constellations.

Though the professional astronomer would be more or less helpless without his telescope, any casual watcher can learn much even if he has no optical aid at all. There is endless variety in the night sky, and there are many fascinating objects to be seen by anyone who knows where and when to look for them. One does not need a powerful telescope in order to take a real interest in astronomy.

April 2 1965 - Astronomy and Astrology

Over the years, I have been referred to many times as 'an astrologer'. There are still some people who confuse astrology with astronomy, and after much deliberation we decided to give a programme to the subject, prompted by the fact that at that time three planets {Mars, Uranus and Pluto) were all in the constellation of Leo.

The results were, predictably, somewhat explosive. Letters from in­furiated astrologers poured in; they ranged from organizers of 'colleges' providing 'degrees' in astrology {at a suitable fee, of course) to one earnest viewer who wrote saying that as I appeared on the television screen, my aura was dull yellow and speckled. All I could do in the latter case was to write back assuring the correspondent that I would do my best to have my aura dry-cleaned before the next programme. There were also letters from flying saucer enthusiasts and followers of the Atlantis cult. I spent many hours battling with the deluge of mail, though with regard to the 'colleges' I admit that I merely put them in touch with each other and took no further action.

The most interesting point about it all was that not one of the astrologers offered any answer to the objections I had put forward. And there were, of course, many letters too from people who were glad that I had pointed out the difference between astronomical science and 'what the stars foretell'.

At the present moment Mars is still a prominent feature of the evening sky. Though it is receding from the Earth, it is still much brighter than any of the stars near it, and its strong red colour marks it out at once. During early April binoculars or low-power telescopes show another planet close beside it; this is Uranus, the third of the remote gas-giants, much larger than either Earth or Mars, but so distant that it is never easy to see with the naked eye. A moderate telescope is enough to show its rather dim, greenish disk, though larger instruments are needed to reveal any of its five satellites.

Uranus lies far beyond Mars, and is in fact very much farther from Mars-than we are. The two planets appear close together simply because they happen to lie in more or less the same line of sight. Both are in the constellation of Leo the Lion - and yet this, too, is merely a conventional means of expression, since even the nearest star is immensely more distant than a planet.

The diagram shows what is meant. The main stars of Leo are shown, together with their distances in light-years. (A light-year, or the distance travelled by light in a period of one year, is equal to rather less than six million million miles.) The curved line of stars which includes Regulus, Gamma, and Epsilon is generally nicknamed 'the Sickle'. Mars, at the moment, is only about 75,000,000 miles away - that is to say, less than seven light-minutes!

To say that Mars is 'in' Leo is therefore decidedly misleading. .After all, a sparrow flying at rooftop-height against a background of clouds is not 'in' the clouds.

There is the further point that the stars of Leo are themselves totally unconnected with each other. Epsilon Leonis is over 250 light-years away from Regulus, which is considerably more than the eighty-four light-years separating Regulus and the Sun. The pattern of the constellation is nothing more than a line of sight effect, and if the Solar System lay in a different direction the stars of Leo might well be spread out all over the sky. In fact, a 'con­stellation' is not truly a constellation at all.

Yet these constellation groups, and the apparent positions of the planets in the sky, form the whole basis of the pseudo-science of astrology, which was widely studied in mediaeval times and which is still taken quite seriously in a few countries, notably India. It was claimed that a person's whole character and destiny was influenced by the positions of the Sun, Moon, and planets against the stars at the moment of birth, and an astrological horoscope was regarded as a most important document. Famous scientists of past times were believers in astrology; even Johannes Kepler, who laid down the famous Laws of Planetary Motion, cast horoscopes (though whether he believed in them is another matter), while the great Sir Isaac Newton was most decidedly a mystic. Still earlier, astrology was thought to be just as important as true astronomy.

Originally the Earth was thought to be flat, and to lie at the centre of the universe. The old Greek philosophers realized that the Earth is a globe, but only a few of them were bold enough to suggest that our world might move round the Sun; indeed, it was not until the sixteenth and seventeenth centuries that the idea of a Sun-centred system became firmly established. Astrology, then, is related entirely to the Earth as a centre.

The mediaeval astrologer was a most influential person. He cast horoscopes for kings and princes, he made weighty pro­nouncements, and sometimes he even predicted the approaching end of the world. Comets were regarded as particularly unlucky, but, according to the astrologers, conjunctions of several planets were even worse.

It is natural that the planets - or some of them - should at times appear close together in the sky; as we have seen, Mars and Uranus are at present only a few degrees apart. But when several bright planets met in the same constellation, in 1524, a famous German astrologer named Stoeffler took the opportunity to fore­cast the end of the world, and caused widespread panic; people even went so far as to build boats and arks so as to escape the expected flood. Much more recently, in 1962, five planets were together in the constellation of Capricorns (the Sea-Goat), and once again the astrologers were much alarmed. In India, parti­cularly, there was great relief when the planets spread out among the constellations once more and the world still survived.

The Sun, Moon, and planets are confined to a certain region of the sky, known as the Zodiac. This is because the orbits of the planets, including the Earth, lie in much the same plane; the inclination is seven degrees for Mercury and less for the remaining planets. There is, however, one exception: Pluto, which is a relatively faint telescopic object, and was not discovered until 1930. (At present it, like Mars and Uranus, will be found in Leo.) The inclination of Pluto's orbit amounts to seventeen degrees, so that it can leave the Zodiac. This is unlikely to worry the astrolo­gers, and in any case the 'signs' of the Zodiac no longer correspond to the actual constellations, since the effects of precession - that is to say, the slight wobbling of the direction of the Earth's axis - have become quite appreciable since classical times. The vernal equinox, or point where the ecliptic cuts the celestial equator, is still known as the First Point of Aries, but by now it has moved out of Aries (the Ram) into the neighbouring constellation of Pisces (the Fishes).

Two of the other planets, Uranus and Neptune, were also unknown to the old astrologers; Uranus was discovered in 1781. Neptune in 1846. If these planets do in fact exert an influence upon human destinies, it would be interesting to learn why the astrologers did not track them down long before the astronomers could do so with their telescopes! There are also the numerous minor planets, or asteroids, which move round the Sun between the orbits of Mars and Jupiter. It is true that they are small in size, but quite a number of them are brighter in our skies than remote Pluto. One of the asteroids, Vesta, is even visible with the naked eye when best placed, whereas Neptune and Pluto, among die 'proper' planets, are always far below naked-eye visibility.

One of the biggest absurdities of astrology lies in the names of die Zodiacal constellations themselves. The familiar groups, such as Leo, Taurus (the Bull) and Gemini (the Twins) are of ancient origin, though it is worth noting that the Chinese and the Egyp­tians used a completely different system. Nobody is quite sure in which country our own constellations were first described. The old Ghaldcean star-gazers may have been responsible; astronomers in the island of Crete have also been suggested. In any case, Ptolemy, last of the great scientists of ancient times, listed forty- eight constellations in his catalogue of the stars. Ptolemy died about a.d. 180; even then, the patterns were very old indeed.

Yet few of the constellations bear the slightest resemblance in outline to the objects after which they are named. It requires considerable imagination to make a bull out of Taurus, a lion out of Leo, or a crab out of Cancer. Moreover, many of the names are mythological; Leo commemorates the Nemaean lion killed by the hero Hercules during his twelve labours. (Hercules is also in the sky, but he is not in the Zodiac, and is much less brilliant than his leonine victim.)

What was evidently done was to draw up arbitrary figures bearing little or no relation to the star-patterns concerned, and then allot names. When this had been done, the astrologers assigned 'characteristics' to the constellations according to the names that had been given. Cancer, the Crab, is said to be a watery sign. Leo, of course, is virile and positive; it is said that the Sun is at its greatest astrological strength when in Leo.

Altogether, the whole procedure seems to be an excellent case of reasoning round in a circle, and it is hard to understand how any thinking person can take it seriously. It is hardly rational to take a collection of totally unrelated stars, make some sort of a figure out of the pattern, give it a name and then claim real significance for it. One can only echo the words of the Duke of Wellington when greeted in the street by a stranger with 'Mr Smith, I believe?' 'Sir - if you believe that, you will believe any­thing.'

Some astrological predictions come true. This is only to be expected; it would be most surprising if they did not, since they cover all sorts of subjects and are usually wrapped up in suitably nebulous language. Now and again some astrologer will achieve a lucky hit, which will be well publicized. The same is true of personal horoscopes, though for every correct statement there are always several which are very wide of the mark.

One typical case may be cited. Not long ago, an astrological magazine forecast the sudden death of President Kennedy, and gave the correct month of the assassination. This prediction was regarded as a convincing justification of astrology - but it must also be related that during the previous three years the same magazine had foretold the death of President de Gaulle, the deposition of General Franco, and the removal of Dr Salazar of Portugal. It is worth noting, too, that in 1938 and 1939 British astrologers were as emphatic as they were unanimous: there would be no war against Nazi Germany.

Only the credulous will believe that line-of-sight effects 0: planets and stars will have any effect upon a man's character or life, but it is nevertheless illuminating to ask a serious astrologer just how these alleged influences occur. I did ask precisely this question of an astrologer a few months ago. His reply was: hasn’t the slightest idea.' This was, at least, a straightforward admission, and differed from the usual attitude. Most astrologer; faced with such a query, would have started talking about mysticism, ancient teachings, and, of course, vibrations. The latter word is a favourite of all devotees of what may be termed the 'fringe' of science; it is also very convenient, because in such a context it may be taken to mean practically anything.

Arguments which have no basis of common sense are always hard to refute. It is so with astrology, which lacks any scientific or logical foundation, and which is a relic of the past, when super­stition was rife and concrete knowledge was very limited. In ancient times, when the nature of the universe was not under­stood, it was natural enough to regard the Earth as of supreme importance, with the remaining bodies set in the sky merely for the sake of Earthmen; in such a climate, astrology could be ex­pected to flourish. By now it has, of course, been completely dis­credited in Europe, though in the East it lingers on.

It is, after all, virtually harmless, and many people are amused to read the 'What the stars foretell' columns in the popular press. It must also be emphasized that professional and amateur astrologers are, in general, completely honest and sincere. They take themselves most seriously; they give each other 'degrees', they put impressive-looking letters after their names, and they offer instruction to the unenlighted, all with the best of intentions. The same can be said of other equally sincere bodies, such as the International Flat Earth Society, which still exists, and the Ger­man Society for Geophysical Research, whose members be­lieve the world to be the inside of a hollow globe, with the Sun in the centre of the hollow and Australia situated somewhere above our heads.

There seems no need to say more. Astrology is not a science, and no person with any scientific background will take it seriously, but its name still leads to a certain amount of confusion. Suffice it to say that astrology and true astronomy are entirely different, and entirely unassociated. Yet the sincere astrologer does little damage, and, like the flat earther and the hollow-globe believer, he means well.

February 12 February 1965 - Balloon Astronomy

In this era of rocket probes and artificial satellites, it may seem a retrograde step to turn back to the humble balloon. Yet as an astronomical vehicle, the balloon has much to recommend it, and it seemed well worth while to devote a programme to balloon astronomy in general.

To an astronomer, the Earth's atmosphere is a source of conti­nual annoyance. It is dirty and unsteady, so that images of celes­tial bodies are always to some extent blurred; to take really long- exposure photographs, of say, the surface of Mars is pointless, since the fine detail will not be registered. From this point of view the Solar System observer is in worse case than the astro­physicist, who is concerned with what are to all intents and pur­poses point sources of light; no star, apart from the Sun, shows a measurable disk even in the largest telescope yet built. However, there are more serious troubles to be faced. The atmosphere is not transparent to radiations of all wavelengths; in a large part of the electromagnetic spectrum it is depressingly opaque, so that astronomical information obtainable at ground-based observa­tories is very incomplete. From this point of view, the practice of setting up large telescopes on high mountains is of little help, though it does improve the clarity of the optical images.

The atmosphere of our world is quite extensive, and traces of it linger on up to at least 2,000 miles above sea-level, but its density falls off rapidly with height. More than 90 per cent of the total air-mass lies below thirteen miles, and more than 99 per cent of the mass below twenty miles; the upper reaches are very tenuous indeed. Unfortunately, the chief blocking-out of radia­tions is due to layers in the ionosphere, that part of the atmosphere which begins at an altitude of forty miles or so. The so-called D. E, Fi and F2 layers range up to more than 100 miles; these are regions where free electrons are found in great numbers, making ±.e levels electrically conducting (and, incidentally, making I ring-range radio communication possible, by bouncing wireless raves of certain frequencies back to earth). The layers are pro­duced by X-rays and ultra-violet rays from the Sun, which act : n the thin air; the X- and many ultra-violet rays are themselves absorbed in the process, so that they do not penetrate to the ground.

Lower down comes the ozone layer, which absorbs most of the remaining solar ultra-violet. If, therefore, we are to study these important radiations, we must send our recording instruments up to great altitudes.

Of course, rockets and artificial satellites can go far above the ionosphere, and even escape from the Earth. Yet they are com­plex and expensive, and in their present stage of development they cannot lift massive telescopes, keep them steady while the observations are being carried out, and then return them safely. Balloons are much easier to handle, and are also vastly cheaper. Their main limitation is that they are incapable of rising to the ionosphere. A height of between 80,000 and 90,000 feet is as much as can reasonably be expected, and so balloon-borne instruments can contribute little to either ultra-violet astronomy :r X-ray astronomy. All the same, the balloon has much to be said in its favour, since it can at least carry heavy equipment above most of the atmospheric mass - thus eliminating blurring and unsteadiness of the images. Moreover, water-vapour and carbon dioxide in the lower air absorb most of the infra-red radiations sent to us from the planets. Balloon ascents overcome mis hazard with ease.

Hot-air balloons date back to the year 1783, and within a few months of the first flight a French scientist, Charles, went up two miles in a free balloon. Yet there is little resemblance between less crude vehicles and a modern scientific balloon, which has : y now become an important research tool.

The main development has been carried out by M. Schwarzschild and his team at Princeton University in the United States, in collaboration with the United States Navy, the National Science Foundation, and the National Aeronautics and Space Administration. The 'Statoscope' flights of 1959, concerned mainly with studies of the Sun, were remarkably successful, and the project has now been extended. With Statoscope II, the over­all height from the telescope to the top of the launch balloon is 660 feet; the balloons together weigh over two tons, and another two tons of ballast are carried for later release if height has to be maintained during the night. The telescope, plus its controls, weighs three and a half tons. Two large parachutes are also carried; in case of emergency, the instruments and their records can be separated from the main balloon system, and brought down gently. Many of the radio and electronic devices used are similar to those of artificial satellites.

The launch of such an enormous, fragile system must be under­taken on a calm day, with a wind speed of less than fifteen miles an hour or so, and takes some time. The inflated launch balloon lifts the long, folded main balloon, the twin parachutes, and the telescopes with its associated instruments and controls. Two large lorries are used to cancel out any ground-wind; finally, when the long train of items is extended vertically, the tethering stay is dropped and the whole assembly rises into the upper air at a rate of 800 feet per minute.

A model of Stratosphere 2 shown is on the left, a view of the actual flight is shown on the right

During the ascent, helium gas from the launch balloon vents into the main balloon, so that at the chosen 'cruising' altitude (about fifteen miles) the main balloon will be fully inflated. At this point, radio commands direct the telescope towards the objects under study. The telescope locks on to each object in turn, while the observations are made. The procedure is far from simple, but is much more straightforward than with an earth satellite or space-probe; the balloon is what may be termed a 'local' vehicle, and is much more under control. The vital ad­vantage is that the actual instruments and records are recovered, to be examined at leisure and in comfort.

The new telescope for Statoscope II would be regarded as very fine even by ground-observatory standards. It is a reflector, with a 36-inch mirror made of fused quartz. The entire telescope unit will be able to point to selected objects in the sky with re­markable precision, and will remain pointing steadily to an accuracy of 1 /50 of arc second of arc. At peak altitude, where the atmosphere is so thin, the telescope will be capable of detecting fine details on the Sun, Moon, and planets only 1/10 of a second of arc across - which is comparable to using a telescope based in London to see a man who is as far away as New York.

Important discoveries have already been made by balloon- telescope techniques. For instance, detailed photographs of the Sun's surface have been taken, showing features beyond the range of ground telescopes. It has long been known that the solar surface is 'granulated', but the individual granules are compara­tively small, and are in rapid motion, so that they are not easy to study. Balloon photographs show them with amazing clarity, and show that the granules are not of uniform size. The structure of sunspots has also been shown in more detail than ever before.

Stellar astronomy has also benefited, but in view of the present emphasis upon rocket probes it may be worth saying something about the balloon results with regard to Mars and Venus.

Mars, where there is an atmosphere - even though a thin one - has been specially studied, particularly with regard to atmos­pheric water-vapour. There is so little moisture that ground-based instruments were unable to detect it at all; its traces were masked by the water-vapour in our own air. Balloon telescopes have been able to observe from heights where terrestrial water-vapour can b e neglected, and for the first time definite traces of moisture have been found in the Martian atmosphere.

The first serious balloon studies of the second of our 'neighbour' planets, Venus, were made in November 1959, by Ross and Moore in the United States. Until then it had been tacitly assumed that the atmosphere of Venus contained no appreciable water- vapour, and the clouds, whatever they might be, were not made t: H20. The balloon results showed otherwise. Instead of being bone-dry, the atmosphere contained more water-vapour than that of the Earth at an equivalent level. These early results have been substantially confirmed by more recent balloon flights, and it also appears that the clouds are composed of ice crystals. (This does not mean that the planet's surface is likely to be refreshingly cool; Venus is almost certainly very hot indeed.)

So far as balloon astronomy as a whole is concerned, we must admit that it will always be limited in scope; a balloon, by its very nature, has a definite 'ceiling'. For studies which involve going up above the shielding layers in the ionosphere the rocket must remain our only answer. Yet there can be little doubt that balloon techniques have proved their worth, and will be widely used in the future. By space-research standards they are very cheap; the main cost lies in the telescopes and other instruments which are to be lifted - but it is not essential to use giant telescopes. Reflectors of, say, forty to fifty inches aperture probably represent the practicable maximum.

Manned ascents for scientific research have often been made, but generally speaking there is no need to risk human life. The records are obtained photographically, and a visual observer on the spot could not add a great deal, interesting though the ex­perience would be. It is the unmanned, instrument-carrying balloon, operating from altitudes of fifteen miles or so, which will prove of most value in the long run.

Almost all modern work in balloon astronomy has been carried out by the Americans, but since the results are so encouraging it is presumably only a matter of time before the Russians join in ; we may hope, too, for British participation. It is too early to say just what the next developments will be, but we may be sure that the balloon, as an astronomical tool, has come to stay.