December 13 1963 - Legends of the Stars

Everyone must be fascinated by the old myths associated with the star- patterns, and the Christmas season seemed to be a good time to present a programme about them. With me was Colin Ronan, who has made a special study of the ancient star-legends.

The first astronomers had no real idea about the nature of the stars. Since no star appeared as anything but a point of light, it was natural to suppose that they were small; since they showed no relative motions, it was equally natural to assume that they were fixed, revolving round the Earth once in twenty-four hours. It was thought, too, that all the stars lay at the same distance from us, probably fixed to some sort of solid sphere.

This sounds far-fetched today, when it is known that the stars are suns and that many of them are much larger and more luminous than the Sun we know. Yet we still have a legacy from the old sky watchers, since the constellation patterns which they formu­lated have never been changed.

Ptolemy of Alexandria, last of the great astronomers of Classical times, died about a.d. 180. In his best-known book, which has come down to us by way of its Arab translation, he virtually summarized the astronomical knowledge of his period. Altogether he enumerated forty-eight constellations; some were named after mythological gods and heroes (Orion, Hercules), while others were supposed to represent everyday creatures and inanimate objects (the Swan, the Fishes, the Cup). All Ptolemy's groups are still accepted, though their boundaries have been modified. Of course, the sky was not completely covered, since the far southern stars were never visible from the Mediterranean area, so that some of the groups near the south celestial pole have strangely modern names - the Microscope and the Octant, for instance.

Astronomers of the seventeenth and eighteenth centuries were not slow to form new constellations, often by 'stealing' areas from the older groups. Some of these have been accepted, and the total number of constellations is now almost ninety, but others were tacitly rejected. Perhaps this is just as well, since the names were cumbersome and the proposed groups totally unworthy of separate recognition. Typical examples are Sceptrum Brandenburgicum (the Sceptre of Brandenburg), Officina Typographica (the Printing Press) and Telescopium Herschellii (Herschel's Telescope - not to be confused with the modern Telescopium), all of which, together with others, are to be found on the star-maps drawn up by the German astronomer Bode about 1780.

Thirty years ago, a commission of the International Astrono­mical Union took the whole matter in hand, and fixed the boundaries of the various constellations with great precision. Even so, it cannot be said that the system is logical, and one is tempted to agree with Sir John Herschel, the great nineteenth-century astronomer, who said that 'the constellations seem to have been almost purposely named and delineated to cause as much confusion and inconvenience as possible. Innumerable snakes twine through long and contorted areas of the heavens, where no memory can follow them; bears, lions, and fishes, small and large, northern and southern, confuse all nomenclature.'

Neither do the constellations, in general, have outlines which correspond even remotely with the objects after which they are named. It takes a highly fertile imagination to make a hunter out of Orion, a bear out of the Great Bear, or a ship out of Argo Navis. Only in a few minor cases, such as the Triangle and the Northern Crown, are the names reasonably appropriate.

Another point of considerable importance is that there is no such thing as a 'constellation' in the real sense of the word. In most cases the various stars in any particular group are not associated with each other, and simply happen to lie in more or less the same direction as seen from the Earth. To show what is meant it will be best to consider Orion, the Hunter, which is among the most spectacular of all the constellations, and which dominates the evening sky during winter and early spring.

Orion is so distinctive that it can hardly be overlooked. It has seven bright stars of which two (Betelgeux and Rigel) are particu­larly prominent. The most casual glance shows that Betelgeux and Rigel are entirely different. Rigel is almost pure white, and exceptionally luminous; a recent estimate makes it about 50,000 times as powerful as the Sun, and its distance from us in the region of 900 light-years. Betelgeux has a strongly orange-red hue, and is not so luminous, but to compensate for this it is of immense size; its diameter is thought to be 250,000,000 miles, so that it is large enough to contain the entire orbit of the Earth round the Sun. It is 520 light-years away, so that the real distance between Betelgeux and Rigel is comparable to the distance between Betelgeux and ourselves. On the other hand Kappa Orionis or Saiph, the star in the lower left-hand corner of the Orion figure, has a distance of more than 2,000 light-years, and is not truly associated in any way with either Betelgeux or Rigel.

An even more graphic case is provided by Aldebaran, in Taurus - 'The Eye of the Bull', a brilliant orange-red star almost in line with Orion's belt. Extending from it may be seen a pattern of several much fainter stars, making a rough 'V', and comprising the Hyades cluster. It looks, at first sight, as though Aldebaran were situated in the Hyades, but this is not so; Aldebaran lies about half-way between the cluster and the Sun. The diagram makes this clear.

The same principle may be applied to the planets, which are relatively very close. When we say that a planet is 'in' a parti­cular constellation, such as Capricornus or Aquarius, what we really mean is that the planet is seen against a background of totally unrelated stars making up a chance pattern which has been given an arbitrary name. The pseudo-science of astrology, which is built around the planetary positions, is therefore totally without scientific basis.

Yet although the constellations are mere line-of-sight effects, and although few of them bear any resemblance to their chosen names, the old myths and legends are fascinating. Orion, for instance, was said to be the son of Neptune and Euryale, and boasted that he could conquer any creature which Earth could produce - whereupon Juno, who was jealous of him, caused a giant scorpion to appear out of the ground and bite Orion in the foot, killing him. Some say the pleadings of Diana, goddess of hunting, led to his being placed in the heavens directly opposite the scorpion (Scorpio), so that he should suffer no further harm from it. Orion and Scorpio may never be seen together; when one is above the horizon, the other is below. Another legend relates how Diana fell in love with Orion, and thus angered Apollo, who persuaded her to try her skill at archery by shooting at a certain object in the sea. She aimed, and hit the distant mark - which proved to be the head of Orion, who had been wading in the waters. Diana's arrow having killed him, the goddess placed him among the stars.

Orion, as befits a mighty hunter, has his retinue around him. In particular there are two Dogs, Canis Major and Canis Minor. The first contains Sirius, the brightest star in the sky; in point of fact it is much less luminous than a giant such as Rigel, and is a mere twenty-six times as brilliant as the Sun, but it is also one of our nearest stellar neighbours, and lies at a distance of eight and a half light-years. There are various other moderately bright stars in the group, but the outline of the Dog is not well marked. Canis Minor has one bright star, Procyon. The rather barren area between the Dogs is filled by Monoceros, the Unicorn, which has nothing to do with Orion and was added to the sky by Hevelius in 1690. On the other hand another small constellation, Lepus (the Hare), is one of Ptolemy's original forty-eight, presumably because the legends tell us that Orion was particularly fond of hunting hares. Lepus is found aptly enough, below the Hunter's feet.

Not far from Orion lies the constellation of Gemini, the Twins. The Twins themselves, Castor and Pollux, are represented by two bright stars unusually close together in the sky, though once more there is no real connection, since Castor is a full ten light-years farther away from us. The two may be found by using an extended line from Rigel through Betelgeux as a pointer, while the rest of Gemini is made up of several lines of stars extending roughly from Castor and Pollux in the general direction of Betelgeux.

In mythology, the Twins were heroes, sons of the Spartan king Tyndarus and his queen Leda. Many legends are associated with them, and they are said to have taken part in Jason's expedition to obtain the Golden Fleece. Pollux was immortal, while Castor was not. When the inevitable happened, and Castor was killed, Pollux was so heartbroken that he was allowed to share his immortality with his brother, so that both were placed in the heavens. It is worth noting, incidentally, that while Pollux is now appreciably the brighter of the two, Ptolemy ranked it inferior to Castor, so that it has been suggested that Castor has faded appre­ciably during the past 2,000 years.

Jason's ship, the Argo, is also to be found in the sky, but unfortu­nately it lies so far south that little of it rises in Britain. Its leading star, Canopus, is the brightest star in the heavens apart from Sirius, but it can never be seen in our latitudes, and only just rises above the horizon in Ptolemy's home-town of Alexandria. Argo is so huge that it has been convenient to divide it into several parts, of which the most important are Carina (the Keel), Vela (the Sails) and Puppis (the Poop).

Another of Ptolemy's original groups is Auriga, the Charioteer or Wagoner. It is marked by one particularly bright star, the yellow Capella, which is almost overhead in Britain during winter evenings, so occupying the zenith position taken during summer evenings by the equally bright, bluish Vega. Close to Capella are three fainter stars arranged in a triangle, known collectively as the Haedi or Kids. Epsilon Aurigae, at the apex of the triangle, is an exceptionally interesting object; it is a binary, and the fainter component is the largest star known, since its diameter is about 2,000,000,000 miles. Epsilon Aurigae is more than 3,000 light-years distant, whereas Capella, at only forty-five light-years, is relatively close to us.

The mythological Auriga was Erechthonius, son of Vulcan, the Olympian blacksmith. Erechthonius was born deformed, and was reared by Minerva without the knowledge of the other gods. When he reached manhood he became King of Athens, and invented the four-horse chariot, for which Jupiter rewarded him by placing him in the sky.

Turning now to the northern groups, we must say something about the two Bears, Ursa Major and Ursa Minor. The famous pattern of seven stars making up the Plough is only part of Ursa Major, though the rest of the constellation is inconspicuous; Ursa Minor contains the Pole Star, Polaris, which is highly luminous and which lies at a distance of nearly 700 light-years.

Ursa Major was originally Callisto, attendant to the goddess Juno and daughter of King Lycaon of Arcadia. Her beauty sur­passed Juno's own, and the jealous goddess was enraged as a result. To protect Callisto, Jupiter changed her into a bear. Unfortunately Gallisto's son, Areas, saw the bear while he was out hunting, and was about to kill it with his spear when Jupiter intervened, turning Areas into a bear also and placing both animals among the stars.

Most celebrated of all, perhaps, is the legend of how Perseus killed the terrible Gorgon, Medusa, and then rescued the princess Andromeda from a sea-monster. All the characters are to be found in the sky; Perseus and the Gorgon's head are there, together with Andromeda and her royal parents, Cepheus and Cassiopeia, while the sea-monster (Cetus) sprawls down toward the southern horizon Constellations added since the days of Ptolemy have no legends attached to them; such are the Lizard (Lacerta), the Little Lion (Leo Minor) and even the famous Southern Cross. However, other 'modern' groups, such as Phoenix (the Phoenix) retain mytho­logical associations.

From time to time it has been suggested that the constellations should be drastically revised, the old figures being abandoned in favour of some easily-remembered and convenient system. Yet the present groupings have been in use for so long that to alter them would mean immense work and inconvenience, since all star-maps and catalogues would have to be amended, and to engage in such a task seems to be pointless. At this stage it would not even be desirable to reject the smallest and least distinctive constellations, such as Leo Minor, which contain no bright stars or important objects, and which really have no claim to separate identity.

Apart from this, it would be a great pity to throw tradition over­board. Though astronomy has long since become an exact science, it still retains its aura of mystery, and the old legends are too fascinating to be forgotten.

August 13 1963 - The Sun in Action

During this programme, in which Professor C. W. Allen (Director of the University of London Observatory) took part, we were able to show parts of the 'continuous solar movie' assembled by observers at Sacramento Peak in the United States. This was the first time that any of the film had been shown in Britain, and it was certainly spectacular.

During the programme I said that solar minimum was expected in early 1964. This seems to have been borne out, though it is of course very difficult to decide upon the precise date of minimum. At any rate, it seems that solar activity should be on the increase again by the spring of 1965.

Sunspots

Sun in Hydrogen Light

 

 

 

 

 

 

 

 

 

Latest images of the Sun taken with the NASA SOHO Satellite

Solar photography began many years ago. There can be few people who have not seen pictures of the Sun, showing the brilliant surface or photosphere together with the darker patches known as sunspots; such photographs are taken daily at professional observa­tories, and are also obtained by amateurs working with modest telescopes. It is much better to photograph a sunspot than to draw it, since the details are often so complex that they are extremely difficult to sketch accurately.

The Sun, a typical star, has an intensely hot surface (6,000 degrees C), while the spots are about 2,000 degrees cooler, appearing dark only by contrast. The precise cause of sunspots is not known, but their behaviour has been extensively studied, and it has been found that their numbers vary in a semi-regular cycle of about eleven years. This solar cycle, first recognized more than a century ago by the German amateur Heinrich Schwabe, is of fundamental importance, since it affects not only the spots but almost all the other features of the Sun.

At a spot-maximum, there may be many groups visible at the same time; this was the case in 1957-58, the time of the Inter­national Geophysical Year. Since then, activity has died down, and we are approaching the period of minimum activity. Large groups are now uncommon, and during August 1963 I recorded several days when the disk was completely clear. Minimum is expected in early 1964, so that the next maximum will not take place until 1969^ or 1970. We cannot be more definite, since the cycle is not constant; the interval between successive maxima may be as short as nine, or as long as thirteen and a half years. More­over, some maxima are more active than others; that of 1957-58 was the most energetic since regular observations of the Sun began.

Spots are often associated with bright irregular patches known as faculae, which lie well above the photosphere, and may be re­garded as luminous clouds hanging in the upper regions. They often appear in positions where a spot-group is about to break out, and persist for some time after the group has disappeared. Then, too, there are the granules, thought to be the tops of gas-currents which rise and fall; they are in constant motion, and each has a width of between 500 and 1,000 miles. There is nothing surprising in this constant turmoil; the surface of the Sun is never calm.

Visual observations can tell us little more, and photographs taken in ordinary or integrated light are of limited value in solar physics, spectacular though they may be. With ordinary telescopes it is impossible to study the Sun's surroundings, except during the rare moments of a total eclipse, when the photosphere is blotted out by the body of the Moon and the solar prominences flash into view, together with the glorious pearly corona. However, much more may be learned by means of instruments based upon the principle of the spectroscope. Spectroscopic analysis has shown that much of the Sun's atmosphere consists of hydrogen - which again is not surprising; hydrogen is much the most plentiful sub­stance in the universe. According to Goldberg and Aller, the percentage number of hydrogen atoms in the solar atmosphere is 81 -8; helium comes next with 18-2, and oxygen third with 0-03, while the remaining elements are even less abundant.

When photographs of the Sun are taken in hydrogen light only, the picture is very different from that of an ordinary view. Bright and dark areas are seen; the distribution of the hydrogen may be studied, and it is possible to detect the violent, short-lived pheno­mena known as solar flares, whose importance it is difficult to overestimate. The photograph given in this book, taken in H-alpha light, shows these features clearly.

Flares are occasionally seen in integrated light. The first case was that of 1859, when two British amateurs, Carrington and Hodgson, saw a pronounced flare by means of an ordinary tele­scope; one of the most recent was that of 23 March 1958, when, at 10.05 G.M.T., Waldmeier was fortunate enough to observe a brilliant flare near a sunspot on the Sun's limb. Yet such opportu­nities are so rare that were it not for spectroscopic equipment our knowledge of flares would be virtually nil.

The true origin and nature of flares is still something of a mystery, but present evidence seems to point to their being storms in the chromosphere, of an electrical nature, the hydrogen atoms being made to glow brilliantly by electrical excitation. They spread through large areas of the chromosphere horizontally, i.e. parallel with the Sun's surface, but there is relatively little vertical movement. They emit charged particles as well as short-wave radiation, and they produce marked magnetic storms on Earth, as well as affecting radio communication. It is probable that emissions from flares will form a major hazard to future space- travellers, and this is one reason why energetic studies of them are now being carried out.

A flare generally takes less than five minutes to form, and has a total lifetime of less than half an hour. It would therefore be instruc­tive to take 'movie' films of flares, so that their development and decay could be studied. This idea is not new; it was first suggested thirty years ago, but until the invention of the special device known as the monochromatic filter, by the French astronomer Bernard Lyot, it was difficult to follow up. The principle of the Lyot filter is complex, but, in brief, it cuts out all light except that of hydrogen, so that when it is used in conjunction with a telescope the observer sees the hydrogen light only. (It is possible to select another element, such as calcium, but on the whole the hydrogen studies are the most significant.)

At the 1958 meeting of the International Astronomical Union, the scheme for making a 'continuous solar movie' was discussed by four solar physicists, headed by Henry J. Smith of the Sacramento Peak Observatory in the United States. It was pointed out that if one picture of the Sun were taken each minute, and the successive frames projected at sixteen per second, the acceleration would be 960 times, so that a fortnight's observations could be condensed into a twenty-minute film. This speeding-up would be ideally suited to showing the development of active centres on the Sun, and for studies of flares. It would, of course, involve using hydrogen light only, but with the Lyot filters readily available this would present no problems.

No single observatory could hope to carry out such a programme. For one thing, clouds would have to be taken into account; for another, there would be gaps during the periods when the Sun was below the horizon. For the movie to be truly continuous, photo­graphs from observatories scattered all over the world would have to be used. Fortunately, such photographs might be expected to be available in view of the establishment of 'solar patrols' for the International Geophysical Year programmes. Finally, Smith and his colleagues selected the fifteen-day interval between July 6 and July 20, 1959, which represented one of the high peaks of the solar maximum, and was particularly well observed. Photographs were obtained from observatories in Britain, France, Japan, Russia, Australia, Ireland, and South Africa, as well as the United States; there were more than 20,000 of them, and the originals varied widely in contrast and density, so that it was by no means easy to make a homogeneous integrated copy. An immense amount of labour was required, and the compilation took over a year even after the photographs had been collected and checked. A few gaps in the record remained, but on the whole the result proved remarkably satisfactory.

During the period covered by the film, records indicated that there were twenty-nine major flares, the most significant of which was that of July 16. This was well recorded from Lockheed Observatory, in America, and was important because it was found to emit cosmic rays with surprising energy. Many smaller flares were also shown, together with associated phenomena of all kinds. The original purpose of the movie film was to provide a pictorial record, but its success shows that the principle may well have important scientific applications, and it will certainly be repeated in the future - not immediately, since the Sun is 'quiet' and flares are relatively uncommon, but certainly at the time of the next maximum.

Mention has been made of the possible space-travel hazard due to emissions from flares. Once an astronaut is above the protection of the Earth's atmosphere, he is exposed to radiations of all sorts, and it used to be thought possible that the danger from radiation would prove a fatal obstacle to interplanetary or orbital flight. This has not turned out to be the case, and none of the pioneer astronauts has suffered harm from this cause. On the other hand, all journeys so far have been of limited duration, and when con­sidering longer trips, lasting for many days, we must not be over­confident. If a violent flare broke out on the Sun, the resulting emissions might have serious consequences for a space-man.

The trouble is that flares cannot be predicted with any degree of certainty, and when they appear they do so very rapidly. It is therefore highly desirable to gain a better idea of the moments when flares are likely to break out - so that astronauts can avoid such times, and, conversely, instrumented vehicles are ready to record the emissions and send back the information. The continu­ous movie technique may prove helpful, though it is too early to make any hard and fast .slafemfjats, It roust he stressed, too, that flares are by no means absent even when the Sun is at its calmest, as it will be in 1964, and outbreaks may occur at any moment. All we can say is that flares, like spots, are much more frequent at solar maxima. It may be that prolonged flights beyond the atmosphere will have to be restricted during the years when the Sun is at its peak, but unless the problems set by the flares can be interpreted, interplanetary travel will always be a somewhat hazardous business even apart from the obvious dangers. On the other hand, further research may show that the flare emissions will not have serious consequences after all. We can only wait and see.

The Sun may be nothing more than an insignificant star in the Galaxy, but to us it is the most important body in the universe; without it, we could not survive for a moment. The more we learn, the more we find that solar activity influences terrestrial pheno­mena. A case in point concerns the density of the Earth's upper atmosphere. At sixty miles, the atmospheric density seems to remain almost constant, but at 200 or 300 miles there are pro­nounced fluctuations, and the extreme upper regions have been contracting ever since the last sunspot maximum. The Russian vehicle Sputnik III, sent up on May 15, 1958, gave proof of this. Its initial height ranged between 135 and 1,167 miles, so that it was appreciably affected by atmospheric resistance, and was not expected to complete more than 8,000 circuits before descending into the lower air and burning away. Actually it went round the Earth 10,037 times, and did not come to the end of its career until April 6,1960. The discrepancy was extremely puzzling at the time, but the answer has now been found. The expected lifetime was worked out according to data obtained when the Sun was at its most active; later on, while the Sputnik was in orbit, solar activity became less. Reduction in upper-atmosphere density was the reason why Sputnik III lasted for more than 2,000 extra circuits.

The solar cycle has equally marked effects upon the Van Allen radiation zones which surround the Earth, but we must remember that these zones are of recent discovery; they were detected only around the time of the last sunspot maximum, and we have not yet been able to follow their changes throughout a complete solar cycle. Fortunately, the co-operative programmes organized for the International Geophysical year proved to be so fruitful that they are being extended, and the observations to be made during the aptly named 'International Quiet Sun Year' are expected to add greatly to our knowledge of solar physics.

We have much to learn. We can watch the sunspots with our telescopes; we can use Lyot filters and other instruments to study the Sun at selected wavelengths; we can obtain detailed photo­graphs, and even movie films - but there are many problems which still remain to be solved, so that every possible technique must be brought into operation. Remember, too, that in finding out more about the Sun, we are also improving our knowledge of the millions of other suns contained in our Galaxy.

May 1963 - To Other Worlds

It is not always realized that the idea of space-travel is very old indeed, and dates back at least two thousand years. For the 1963 May programme, Dr Anthony R. Michaelis, the well-known science writer who is now science correspondent of the Daily Telegraph, joined me in discussing some of the old ideas - many of which seem far-fetched enough to-day, but some of which are nevertheless of the highest interest.

The science fiction of yesterday is changing rapidly into science fact. It is not many years since the idea of space-travel was regarded as a fantastic dream and even in the nineteen-forties and early nineteen-fifties there were various eminent scientists who were con­vinced that it would never be possible to send a vehicle to the Moon, to say nothing of Mars or Venus. Yet the dream itself is very old indeed, it goes back at least as far as the second century a.d., when the Greek satirist Lucian wrote a book about a lunar voyage, and probably it goes back even further.

This is not surprising. What is, perhaps, unexpected is that many of the old ideas contain suggestions which have proved to be extremely valuable. Therefore it is certainly not a waste of time to look back into the past, and see how the theme of inter­planetary travel has been gradually developed.

There was little science in the first 'space stories', at least with regard to the methods of travel, and yet they are still worth reading. One of the pleasantest, and most famous, was written by an English bishop, Francis Godwin, probably in the sixteen-thirties (it was published posthumously in 1638). The title was Man in the Moone; it appeared in many editions, and is certainly better remembered today than Godwin's vast catalogue of English bishops and his various theological works.

In the story, Godwin's hero, Domingo Gonzales, trains some gansas, or wild swans, to tow him through the air in a raft. It is only when he is thoroughly airborne that he realizes that the birds hibernate on the Moon, and are taking him there regardless of his personal wishes. When he arrives, he finds a highly advanced civilization. The people, some of whom are thirty feet tall, live a Utopian existence, and speak a language so musical that it can be written down only in note form. They abhor uncleanliness, and any children who show signs of latent wickedness are at once dis­patched to Earth, where there is so much wickedness already that a little more will not matter!

Another science-fiction writer of the same period was no less a person than Johann Kepler, the great mathematician and astronomer, who produced a strange story called the Somnium. Here there is a supernatural element, since the traveller, Duracotus, is carried to the Moon by demons, but at least Kepler made provision for the fact that most of the journey would have to be done in airless space, and he described how Duracotus was given special sponges, moistened and held to the nostrils, to help him to breathe.

Mention should also be made of the interplanetary adventures of the famous Baron Munchausen, written by R. E. Raspea serious scientist who has the dubious distinction of being one of the few men ever to have been expelled from the Royal Society (for embezzling the scientific medals in his charge). Then, too, there was Cyrano de Bergerac, who in one story made use of’ firecrackers' and therefore anticipated the idea of rocket propulsion, though probably without any idea of its significance. But the first serious suggestions for interplanetary flight were made by Jules Verne in his classic From the Earth to the Moon, published in 1865. We now know that Verne's scheme can never be put into practice; but it is only too easy to be wise after the lapse of almost a hundred years.

Verne planned to fire his adventurers to the Moon in a hollow bullet, or projectile. The cannon, known as the Columbiad, was built at Stone's Hill, in Florida, not far from the modern rocket ground at Cape Canaveral,* and the launching velocity was to be seven miles per second. Detailed calculations were given in the story, and these calculations were basically correct. Seven miles per second is the Earth's escape velocity, as Verne knew well. Fired at a lesser speed, the projectile would fall back to the Earth; if sent up at full escape velocity, it might well land upon the Moon. Since this would be a 'one-way’ journey only, Verne, in his sequel (Round the Moon, 1870) introduced a minor earth satellite, which perturbed the projectile and swung it right round the Moon, so that eventually it fell back on to the Earth - landing in the sea close to the point where at least two American astronauts have since been picked up.

Unfortunately, there were two facts which Verne ignored, probably because he did not realize their importance. First, a projectile starting off at seven miles per second through the dense lower layers of the Earth's atmosphere would set up so much friction that it would be destroyed immediately. Secondly, the shock of departure would certainly prove fatal to any occupants of the projectile. Yet Verne cannot be blamed - and it is worth noting that in our own century two of the rocket pioneers, Hermann Oberth and Guido von Pirquet, thought it worth while to investi­gate the possibilities of building a space-gun on top of a mountain and then evacuating the barrel of the cannon, each of which pre­cautions would reduce air-resistance. They concluded that, even so, the heat generated would be fatal; but if they were initially uncertain about it, it is not surprising that Verne fell into the same trap.

There is, however, one bad mistake in Round the Moon. This concerns the so-called 'neutral point', where the Earth's gravity balances that of the Moon. According to Verne, the travellers gradually lost 'weight' until by the time they reached the neutral point they no longer weighed anything at all: 'Their heads vacillated on their shoulders. Their feet no longer kept at the bottom of the projectile . . . Suddenly Michel, making a slight spring, left the floor and remained suspended in the air'. As they passed the neutral point, and fell toward the Moon, their weight returned.

This is quite wrong. Actually, the travellers would have been in free fall, and therefore weightless, from the moment of their launching, while the 'neutral point' is of no importance or signi­ficance whatsoever. All the same, Verne did at least take loss of weight into account, and his travellers found it no more unpleasant or uncomfortable than Shepard and Glenn, Gagarin and Nikolayev have done in recent years.

Verne did, moreover, use 'recoil rockets' at one point in his story, and it is also noteworthy that in another book, published in 1879, he described an artificial satellite. This particular novel, The Begum's Fortune, cannot rank with his lunar stories, but it contains at least one important idea. A German industrialist, Professor Schultz, decides to destroy the city of Frankville by means of a large projectile filled with poison gas. The projectile is duly fired - but it reaches orbital velocity, and passes harmlessly over Frankville, entering a closed path round the Earth and so becoming one of the first artificial satellites in literature.

Jules Verne died in 1905. Though he can hardly be termed a scientist, he was most certainly a pioneer, and it is significant that when the Russians photographed the reverse side of the Moon, in 1959, they named a large and important lunar crater in Verne's honour.

Even before Verne's death the idea of using rocket propulsion for space-travel had been put forward by an extraordinary man who was a dreamer as well as a scientist. This was Konstantin Eduardovich Tsiolkovskii, half Polish and half Russian, who spent most of his life teaching mathematics in a Russian country school. Tsiolkovskii was purely a theorist, and never actually fired a rocket in his life, but in many ways he was decades ahead of his time. His first scientific papers on the subject date from 1895, and the most important article appeared in 1903 (it had actually been written four years earlier). It attracted little attention, since it came out in a small journal and was not translated into other languages until much later, but it contained many suggestions which have since been put into practice. For instance, he planned to use liquid-fuel rockets, and to make use of the step-launching principle.

Almost as interesting, in its way, is Tsiolkovskii's novel Beyond the Planet Earth, which was not published until 1920, but which had evidently been written before the turn of the century. As a story, little can be said in its favour, but as a forecast it was truly remarkable, and it contains notes on space-suits, rockets with a strangely modern look about them, zero gravity, and even inter­planetary navigation, together with problems of food and air supply. The scene is set in a.d. 2017; selected scientists from all nations have assembled at a base in the Himalayas to carry out space-research investigations. It may be worth commenting that we can only hope space-research will in fact become international long before a.d. 2017!

By the time Tsiolkovskii died, in 1935, he had become world- famous, but rocket research had shifted from Russia to Germany and the USA. In America, in 1926, R. H. Goddard fired the first successful liquid-fuel rocket; in Germany, members of the short lived but energetic 'Society for Space Travel' undertook launchings of their own. One of the German pioneers, Wernher von Braun, later played a major role in the development of the V-2 rocket, but by then the original Society had been disbanded, and in Nazi Germany the emphasis was wholly upon weapons of war. Yet it is extremely interesting to look back at some of the early space-ship patterns. For instance, the design produced by H. Oberth in 1928 is far closer to the modern rocket than the Wright Brothers' primitive Flyer could ever have been to a stratocruiser.

By the end of the war, it had become clear that the rocket had immense potentialities - and everyone is familiar with the rapid developments which have occurred since then. Of the two last- century 'dreams', therefore, the space-gun has proved to be impracticable, while rocket propulsion has more than fulfilled expectations. There remains another idea about which not a great deal can be said as yet: the principle of anti-gravity.

We have to admit that at the moment we know little about gravity, and we certainly have no idea of how it might be shielded, but among novelists the theme was already becoming popular by the end of the nineteenth century. First in the field seems to have been Robert Cromie, who wrote his book A Plunge into Space in 1891, and dedicated it to Jules Verne (who wrote a foreword to it). Here, a party of scientists travels to Mars and back in an anti- gravity 'steel globe', and it may be of interest to quote a few lines from this little-known book. They are spoken by the leader of the expedition, Henry Barnett:

The attraction of gravitation is but another phase of the force which compels a needle in Liverpool to answer the fluctuations of another in New York. Cut the intermediate wire by which the force is conveyed, or insulate one needle, and the other ceases to act. The space between the Earth and Mars is, as it were, one vast charged wire. Along that intangible line of communication you might send a telegram as easily as under the Atlantic Ocean. Nay, more, a body insulated from the Earth's attraction would by it pass almost instantaneously to Mars, for the attraction of gravity is inconceivably rapid.... My chief difficulty - indeed, my only difficulty worthy of the name - has been to regulate the speed at which we travel. .. . Tonight, simply by the turning of two screws, I shall insulate the Steel Globe from the Earth's attraction, and all who choose to journey by it will pass safely on to Mars.

The anti-gravity theme was also used by the German writer Kurd Lasswitz, in 1897, in his book On Two Planets (Auf Zwei Planeten), which, unfortunately, has never been translated into English. Lasswitz also described a sophisticated artificial satellite, built by the Martians and remaining stationary at a height of 6,356 kilometres above the Earth's North Pole. More famous is H. G. Wells' The First Men in the Moon, which appeared in 1901.

Here, the travellers reach the Moon in a sphere made from an anti-gravity substance, 'cavorite', and navigate themselves by judicious opening and shutting of the cavorite blinds.

Until fairly recently the idea of anti-gravity was regarded as scientifically absurd, but nowadays the situation is not so clear-cut. There have been suggestions that in some parts of the universe there may be 'anti-matter', also composed of fundamental particles, but with properties completely opposite to those of the matter of which we are composed. If this proves to be correct, there is presumably no reason to reject the whole idea of negative gravity. At any rate, research work into the question of anti-gravity is now being carried out in the United States, and presumably in the Soviet Union as well. It is impossible to tell whether anti-gravity techniques will be mastered in the foreseeable future, but the prospect is an in­triguing one.

Progress is now so rapid that it is dangerous to make predictions for more than a few months ahead, but at least it is clear that some of the devices now in regular use would have been regarded as fantastic science fiction in the days of Edward VII. The lesson is, surely, that the true scientist cannot afford to laugh at the proposals of the scientific dreamer.

* Now known as Gape Kennedy.

April 17 1963 - Exploding Stars

The appearance of a nova, or 'new star', always causes considerable interest in astronomical circles. The nova of 1963, discovered by E. Dahlgren in Sweden and independently detected by the American observer L. Peltier, was no exception, even though it never became brilliant enough to be striking. It seems to have been a perfectly ordinary nova, and faded in the conventional way, though by mid-1964 it was still observable with moderate-sized tele­scopes.

One of the more interesting astronomical events of 1963 has been the appearance of a comparatively bright nova, or 'new star', in the constellation Hercules. It was discovered by the Swedish amateur Dahlgren, who was using nothing more elaborate than a pair of binoculars, and for some time it was clearly visible to the naked eye. It has proved to be what is termed a 'slow nova', and its fading has been relatively gradual. It has now dropped below naked-eye visibility, but is still an easy telescopic object.

The nova attracted comparatively little attention - except among astronomers — partly because of the spectacular develop­ments in space research taking place during the same period, and partly because it was not well situated for observation during the evenings. Those who were anxious to see it properly had no alternative but to get up in the very early hours of the morning, and it is understandable that the bitter weather made all but the genuine enthusiasts disinclined to do anything of the sort.

However, the nova was not difficult to locate, since it lay fairly close to the brilliant star Vega, in Lyra. For some time there were doubts about whether its position was in Lyra or Hercules, since it was almost exactly on the border between the two constellations; eventually the International Astronomical Union decided that it lay just within the boundary of Hercules.

Dahlgren's star has been the brightest nova for some time. Excluding Nova Argus of 1942, which was extremely difficult to see from England because of its southerly declination, there have been only two brighter novae during the past thirty years; one in Hercules (1934) and the other in Lacerta, the Lizard (1936). There have, however, been half a dozen fainter novae, and it has become clear that such objects are not particularly uncommon. There have in fact been no fewer than eighteen observed novae in our own Galaxy during the present century.

Strictly speaking, a nova is not a 'new' star at all. What apparently happens is that a formerly obscure star suffers an out­burst which results in a striking but temporary increase in lumi­nosity. When the outburst subsides, the star returns to its old state, or basically so - from which it may be inferred that the disturbance is largely limited to the star's outer layers.

It is tempting to explain a nova as the result of a direct collision between two stars. No doubt this would cause an outburst on a grand scale, but we may be sure that the explanation is wrong. The stars are widely scattered in space, and even in the more densely populated parts of the Galaxy collisions must be exces­sively rare. Yet novae, as we have seen, are not rare; nearly thirty have been observed since the invention of the telescope in the first decade of the seventeenth century, and no doubt a great many more have escaped detection. An alternative theory, that a star passes through a dark nebula and interacts with the nebular material, is more plausible but has serious weaknesses, and there can be little doubt that disturbances in the star itself are responsible. Before saying more about the causes of novae, however, it will be as well to deal briefly with some of the more important 'stellar explosions' of modern times.

Particularly notable was Nova Persei 1901, discovered by a Scottish amateur, Dr Anderson. (This, incidentally, was Ander­son's second success; he had also discovered the less spectacular Nova Aurigae 1891.) At its maximum, Nova Persei reached zero magnitude, so that it was fully equal to Vega and Capella. Its rise was extremely rapid: two days before Anderson saw it as a prominent naked-eye object, the region had been photographed at the Harvard Observatory, and it was found that the nova was then a dim object of magnitude 13. It reached maximum a couple of days after its detection, and then began to fade; within a month it had dropped to the fourth magnitude, and continued to fall, though with fluctuations. At last, thirty years after the outburst, it had reached its pre-nova brightness. Its distance is estimated as about 1,550 light-years. The exact value is by no means certain, but we may assume that the explosion actually took place during the far-off days when Britain was still occupied by the Roman legions - though the light-rays did not reach Earth until our own century.

A few months after maximum, Nova Persei was seen to be immersed in what appeared to be an expanding nebula. The rate of expansion was calculated, and proved to be impossibly great. The Dutch astronomer Kapteyn provided what we now know to be the correct explanation. The star was immersed in a cloud of gas and dust which had previously been invisible; after the out­burst, the radiation from the nova lit up the cloud, and of course the inner parts of the cloud were illuminated first, since light travels at a finite velocity. The apparent result was a nebula expanding at the speed of light, whereas in fact there was probably no expansion at all. (Like most or all novas, the star did throw off an expanding shell, but this was a different phenomenon.)

The next really brilliant nova appeared in Aquila, the Eagle, in 1918. It exceeded even Nova Persei, and reached magnitude — 1 - i, so that of all the 'fixed stars' only Sirius outshone it. Here too there was an expanding shell; after eighteen months it had taken on the appearance of a disk about the same apparent size as the planet Neptune, and it continued to increase, at the rate of about two seconds of arc per year, until 1941. After that, the shell became so faint that it could not be observed further.

One of the difficulties about studying the full careers of novae is that we have insufficient knowledge of them in the pre-outburst stage. There are so many faint stars in the sky that we cannot hope to study them all, at least in detail, and a star which suffers a nova outburst does so without the slightest warning. Fortunately, the pre-outburst spectrum of Nova Aquilae has been recorded, and classed as of type A; in other words it had been a white star, with a spectrum not very different from that of Sirius or Vega. It is reasonable to suppose that only comparatively hot stars turn into novae. The Sun, which is a yellow dwarf of spectrum G, does not come into this category.

Passing over the novae of 1920 (in Cygnus, the Swan) and 1925 (in the southern constellation of Pictor, the Painter, invisible in England) we come to the interesting Nova Herculis 1934. It was discovered in December of that year by J. P. M. Prentice, a British amateur who was (and, happily, still is) a celebrated observer of meteors.

Prentice was not searching for novae at the time. He had been studying the Geminid meteor shower, and after a spell of observing he went for a casual stroll; on looking up at the region of the Dragon's head, he suddenly noticed an unfamiliar star of between the third and fourth magnitudes. This nova, too, lay just

within Hercules, not far from the spot where Dahlgren's star appeared a few weeks ago.

Nova Herculis 1934 brightened up to the first magnitude, so that it surpassed the famous Deneb in Cygnus. It had an unusually long maximum, and remained visible to the naked eye for some time. By now it has become extremely faint, but is still visible in moderate telescopes, and is a most interesting object. Apparently it is a binary system; that is to say, there are two stars, moving round their common centre of gravity. One, the old nova, is surrounded by a compact nebula; the other is thought to be a dim Red Dwarf, much feebler than our Sun. The distance is in the region of 750 light-years, so that the outburst actually took place before the signing of the Magna Carta.

Two more conspicuous novae have been seen since then. The 1936 star in the little northern group of Lacerta became as bright as the Pole Star, but faded rapidly; it too threw out a shell of gas which expanded at the unprecedented rate of about 2,400 miles per second. Then, in 1942, came the nova in Argo Navis, the Ship. It lay in that part of Argo known as Puppis (the Poop), but, as noted earlier, was very badly placed for European observers. At its most energetic it is thought to have been at least 1,500,000 times more luminous than the Sun. Mention should also be made of the 1960 nova, again in Hercules. It was discovered by Olaf Hassell, of Norway, and was just visible without a telescope when at maximum.

There seems to be a definite link between novae and some types of irregular variable stars. We even know of 'recurrent novae', which have suffered more than one outburst; T Coronae, for instance, blazed up to the second magnitude in 1866, faded in the usual way, and then had another maximum of the third magnitude in 1946. Entirely different are the rare supernovae, of which three have been seen in our Galaxy during the past 1,000 years.

In 1054 Chinese and Japanese observers noted a strikingly brilliant object in Taurus, the Bull, not far from Orion. It became bright enough to be visible in broad daylight, and lasted for months, but when it faded below naked-eye visibility all track of it was naturally lost. Later, in the telescopic era, a curious gas-cloud was found in precisely the position of the 1054 star; it is now known as the Crab Nebula, and is visible with a very small instrument, though photographs taken with powerful telescopes are necessary to show it properly. There is not the slightest doubt that the Nebula represents the wreck of the old star, and it is equally certain that we are dealing with something much more significant than a normal nova. The gas-cloud is still expanding from the old explosion-centre, and has now attained a diameter of three light- years, or well over 17,000,000,000,000 miles.

Another supernova appeared in 1572 (Tycho's Star, so called because great attention was paid to it by the famous Danish astronomer Tycho Brahe), and it is probable that a star studied by Johann Kepler in 1604 was also a supernova. Since then, none has been recorded in our Galaxy - which is a matter for regret, since the telescopic era has been entirely devoid of them. However, supernovae have often been seen in external galaxies. The most celebrated of these appeared in the Andromeda Galaxy in 1885, and was close to naked-eye visibility even at its colossal distance of over 2,000,000 light-years. At maximum, it may have been 200,000,000 times as luminous as the Sun. Even so, it is not the most luminous supernova ever recorded; this distinction must go to an object which was seen in 1937 in a much more remote system, and seems to have equalled 350,000,000 Suns.

The essential difference between a nova and a supernova is that a nova returns eventually to its old state, whereas a supernova does not. In fact, a supernova outburst destroys the star in its old form. It is significant, too, that the Crab Nebula is an energetic source of radio waves, and it is extremely probable that many of the radio sources in our Galaxy are nothing more nor less than supernova wrecks.

When we return to the more normal novae, and try to find an explanation for them, we are faced with the general problem of how a star radiates. Basically, it is known that the source of stellar energy is to be found in nuclear reactions; in the Sun, for instance, hydrogen is being transformed into helium, with the release of energy and a steady loss of mass. The whole process is delicately balanced, and an average star continues to shine with a more or less constant output for a very long period. It may well be that if the nuclear processes become 'out of control', so to speak, a violent disturbance results, with a nova-like outburst affecting the outer layers. A supernova outburst must presumably affect the whole star, and not merely the outer portion.

Much remains to be learned about these remarkable stellar explosions; modern theories appear to have a solid foundation, but many of the details remain to be worked out. This is why astronomers are anxious to study any conveniently bright novae as closely as possible. The appearance of a supernova in our Galaxy would be a welcome event, and by the law of averages it seems that one is due, but we cannot tell when it will occur; it may be tomorrow, it may be next month, it may not be for centuries to come. At any rate, we may be certain of one thing: when the next galactic supernova blazes forth, it will do so with dramatic suddenness, and will take us by surprise.