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.

December 11 1964 - How old is the Earth?

The question of the Earth's age has long fascinated both scientists and non-scientists. For the Christmas programme of 1964, in which I was again joined by Henry Brinton, this problem was discussed, but I have had to make revisions to the article as then printed, because new information is now at hand. We gave the value for the Earth's age as 4,500,000,000 years, which was then the official figure. Subsequently, studies have been made of the Rocks of St Paul, which lie between Africa and South America. They contain the element rubidium, which decays spontaneously, by radio­active processes, into strontium; the half-life is 46,000 million years, so that the decay is hardly rapid. From these researches, it is evident that the Rocks of St Paul are about 4,500,000,000 years old, so that the Earth itself must be still older; in the article below, I have revised the figures and given the currently accepted age. It may still be wrong to some extent, but, as I said originally, it is certainly of the right order.

The last months of 1964 were interesting to the astronomer and the space-research worker; in particular there were three attempts to send probes toward the planet Mars.*

One of the objects of the space experiments is to find out more about the Martian atmosphere, which is much thinner than that of the Earth. Mars is also short of water, and it has often been described as a planet older than the Earth. This is not strictly accurate. It may well be in a more advanced state of evolution, mainly because of its smaller size, but there seems little doubt that its absolute age is very similar to that of our own world. Most authorities agree that the planets in the Solar System were formed in the same manner, and at the same epoch.

We are by no means certain how the planets came into being.

The tidal theory made popular by Sir James Jeans, according to which the planets were pulled off the Sun by the action of a passing star, was widely favoured for some time, but has now been rejected because the mathematical objections to it are fatal. More recently, C. von Weizsacker has suggested that the Sun once passed through a cloud of gas and dust in space, collecting the material out of which the planets were gradually built up. This idea seems promising, but the whole question is still wide open. So far as the age of the Earth is concerned we are on rather firmer ground, and the figure now generally accepted is 4,750,000,000 years.

Authorities of a few hundred years ago would have found this impossible to believe. The account of the creation given in the Bible was taken literally, and it was thought that the world could not possibly go back more than a few thousand years. By adding up the ages of the patriarchs, and making similar calcu­lations which seem naive today, the seventeenth-century Arch­bishop Ussher of Armagh claimed that the Earth came into existence in the year 4004 B.C.; the final figure given was nine o'clock in the morning of 23 October. Many churchmen were satisfied with this, and the matter was generally regarded as settled.

The first serious doubts arose with the development of geolo­gical science. Toward the end of the eighteenth century James Hutton, the first great British geologist, went so far as to declare that 'in the economy of the world I can find no traces of a begin­ning, no prospect of an end'. Hutton belonged to the uniformtarian school of thought - that is to say, he explained the charac­teristics of the Earth's crust in terms of processes that were going on unceasingly, albeit very slowly. It did not take many more years for geologists to gain a fair idea of the vast periods of time required for the development of geological strata, and Ussher's date began to look painfully inadequate.

Orthodox churchmen tried to escape from this dilemma by supposing that although the Earth itself might be very old, the simultaneous creation of species would allow life to be of recent origin. However, difficulties soon arose here, too. Palaeontologists, headed by the French scientist Cuvier, showed that fossils - the remains or traces of long-dead creatures - were to be found in rocks of immense age; since the fossils could not be younger than the rocks which contained them, living things must also be dated back a long way.

A last-ditch stand was made on the assumption that Man might be a recent creation. Of course, it is true that the history of man and his ancestors is brief compared with the age of the Earth, but even so it is to be measured in hundreds of thousands of years, just as the history of mammals has to be measured in tens of millions of years. The decisive evidence was provided by a Frenchman who rejoiced in the name of Jacques Boucher de Crevecoeur de Perthes, who undertook some researches in grave pits and quarries near his home town of Abbeville and discovered flints which had unquestionably been fashioned into shape by human hands. De Perthes continued his work, and by 1838 he had become convinced that men had lived in France at a period much earlier than had been generally thought. In fact, the artefacts dated back far before the period assigned to the Biblical Flood.

It took De Perthes many years to persuade others even to look at his artefacts, but eventually he won his point, and in 1859 he had the satisfaction of having his theories vindicated and acknow­ledged before the British Association and the Royal Society.* The work of Darwin completed the change-over in thought, and the way was at last clear for a proper scientific inquiry into the Earth's age. Geology showed that the time-scale must be very long. Quite apart from strata and fossils, there were several means of proving the Earth's antiquity. For instance, a fair estimate can be made of the rate at which sodium finds its way from the land into the sea; the oceans must originally have been of fresh water, and al­though there are many complicating factors it was clear that to make the sea as salty as it is now would take millions of years. Calculations were also made of the rate at which large rivers, such as the Mississippi, were washing sediment into the ocean, which provided an estimate of the age of sedimentary rocks.

At this stage there was a conflict between the geological and the physical evidence, and Lord Kelvin tackled the problem from three directions. First, there was the question of the rate at which the Earth had cooled down (assuming, as most people then did. that it had originally formed part of the Sun). Given that it started at a certain temperature and cooled at a calculated rate, it was possible to work out the time needed for the Earth to reach its present condition.

Kelvin's second yardstick was the rate of the Earth's rotation. It was known that the length of the 'day' is slowly increasing, because of tidal forces, and for various reasons Kelvin calculated that going back 1,000,000,000 years, the Earth must have been spinning 15 per cent quicker than it is at the moment. If the crust were formed about this time, he reasoned, the Earth's globe would be much more flattened than it actually is, whereas if the Earth solidified only 100,000,000 years ago then the shape of the Earth would be approximately as measured now, with a difference between the polar and equatorial diameters of less than thirty miles. Finally, Kelvin believed that the Sun could not have existed in its present form for as much as 500,000,000 years. Originally he had attributed the Sun's radiation to the kinetic energy of meteors falling on to its surface, but when this theory had been disproved he adopted Helmholtz's suggestion that the source of solar energy lay in gravitational contraction. Kelvin concluded that the Earth must be somewhere between 20,000,000 and 100,000,000 years old. He favoured the lower limit, even though it was far too short to satisfy the geologists.

The argument between physicists and geologists was not settled until more became known about the nature of matter. With the discovery of radioactivity, for instance, the 'cooling Earth' idea ceased to be valid, and the much later investigations into the source of stellar energy showed that the Sun is much older than 500,000,000 years. The Sun radiates not because of meteoric in fall or gravitational contraction, but because of nuclear processes taking place deep inside it; hydrogen is being converted into helium, admittedly by a somewhat roundabout method, so that mass is being lost and energy produced. The mass-loss is 4,000,000 tons per second, but this does not amount to much relative to the total mass of the Sun's vast globe.

It was radioactivity, too, which gave a really reliable means of working out the age of the oldest rocks. Many rocks contain uranium, the heaviest element known to occur naturally, and it is known that uranium decays spontaneously, ending up as an isotope of lead. The rate of decay, so far as is known, is quite unaffected by environment, and is assumed to be constant. The 'half-life' of uranium-238 (that is to say, the time taken for half the original quantity to decay) is more than 4,000,000,000 years. If, therefore, uranium and uranium-lead are found together, the ratio of the amounts is a pointer to the time during which the decaying has been in progress.

On this basis, the oldest rocks seem to date back around 4,000,000,000 years. This agrees well with the geological evidence, since a figure of 1,500,000,000 years has been suggested for some sedimentary rocks while life is thought to have appeared upward of 3,000,000,000 years ago. Taking all the facts into account, it seems that the Earth began its separate existence about 4.750,000,000 years ago. This estimate is not precise, but there can be little doubt that it is of the right order.

Nobody can possibly visualize what this figure really means, but some idea may be gained by means of a scale in which the age of the Earth is taken as one day (twenty-four hours). A table may then be drawn up, as follows:

So if we take the Earth's age as being scaled down to one day, men have existed only during the last couple of seconds. In a way, the old churchmen were right in supposing mankind to be a very recent addition to the scene, but we have certainly learned a great deal since Archbishop Ussher fixed the date of the Creation so exactly as October, 4004 b.c.

Old though it is, the Earth is still only about half-way through its expectation of life. Its eventual fate will, of course, be linked with that of the Sun. Opinions have changed here, too. It used to be thought that the Sun was gradually cooling down, so that it would eventually turn into a dim red dwarf star - in which case all living things on Earth would be frozen to death. This whole theory is wrong. As the Sun ages, and uses up its hydrogen 'fuel', it will become more luminous, and in from 8,000,000,000 to 10,000,000,000 years' time it may well become a red giant, with a cooler surface but a much greater size and luminosity than the Sun we know. If so, the atmosphere of the Earth will escape, the oceans will boil, and all life here will perish - it is even pos­sible that our world will be destroyed.

The crisis lies so far ahead that speculation is rather pointless. Modern theories about stellar energy are subject to constant revision, and we cannot claim to know more than a very small part of the truth. All we can say is that if we are on the right track, then the eventual fate of all Earth creatures is likely to be a heat death rather than a cold death. If intelligent beings still survive here at that remote epoch, the only solution will be to migrate elsewhere. However this may be, we may be sure that there is no fear of any-imminent disaster. The Earth has existed for more than 4,000,000,000 years, and it will remain habitable for at least an equal period of the future. It will not last for ever, but nothing in the universe is eternal - perhaps not even the universe itself.

October 30 1964 - The Earth seen from space

In October 1964 the Soviet vehicle Voskhod went into orbit round the Earth. Its captain was Colonel Vladimir Komarov, who later lost his life when his space-craft came down out of control, so that there is bound to be a certain sadness when reading of his earlier, successful flight.

It was in late 1964 that the space programmes seemed to be gathering momentum, and there was speculation as to what the Earth would look like if it could be seen from a great distance. I discussed this with K. H. Fea, of the Space Research Group at University College, London, and we showed some of the current photographs. Since then, of course, the Earth has been photographed by the U.S. Orbiter vehicle, which was then in the region of the Moon ; and the results are very much as had been anticipated.

The first manned space-flight took place on 12 April 1961, when Yuri Gagarin made a single circuit of the Earth in the original ' Vostok' craft, landing after a flight lasting for less than two hours. Since then other men and one woman have been into space.

The flight of the Soviet vehicle 'Voskhod' (Sunrise) was made on 12-13 October 1964. In many ways it represented a distinct ad­vance, even though it was of comparatively short duration. The ship carried a crew of three men, of whom only one (Vladimir Komarov) was a true 'astronaut'; of the others, Konstantin Feoktistov was a scientist, while Boris Yegorov was a doctor. In view of the potential hazard due to radiations in space, there was every reason to send up a medical man, and Yegorov's findings will be of particular interest and importance when they are made known in full.*

The 'Voskhod' made sixteen orbits and landed safely, ap­parently in the position intended. It made a 'soft' descent; on this occasion the crew members were not separated in ejector- seats, so that the procedure seems to have been similar to that which will have to be adopted for a landing on the Moon. It has been stated that the ship could well be used for a further trip, and that it is totally undamaged. There have been suggestions that the flight was terminated prematurely, and that the astronauts received a heavier "dose of radiation than had been expected; however, the Russians say that this is not the case, and that the 'Voskhod' was not intended to stay aloft for more than the actual period of twenty-four hours seventeen minutes.

It is worth noting, too, that on this occasion the astronauts wore normal clothes instead of space-suits. Food included roast beef, which was sliced and vacuum-packed in polymer film; slices of filleted Caspian roach, and even caviar sandwiches. Communications with the space-craft were excellent throughout, and the Russians claim, no doubt justifiably, that the whole flight was an unqualified success.

The altitude of the 'Voskhod' ranged between 110 and 255 miles, which meant that the crew members could see over large portions of the Earth. During the first orbit they have related how they saw the forests of Siberia; when passing over darkened Australia they looked at the lights of the great cities, while Antarctica was distinguished by its white ice-cap. Of particular interest was their description of what may be called 'cosmic dawn'. Since the revolution period of the space-ship was only just over ninety minutes, a total of fifteen 'dawns' was observed during the trip, and Yegorov's own description is worth repeating:

The atmosphere brightens. It grows yellow, then darkens again, after which appears the blue halo. Then an orange strip appears, which becomes brighter and brighter. At last the edge of the Sun comes into sight, and suddenly it is clear, like a brilliant red oval. Its brightness increases quickly, since sunrise in outer space lasts for only a few seconds . . . The Moon looks the same as it does from the Earth, the only difference being that the sky around is absolutely black.

A display of aurora australis was also observed.

All this is in agreement with the descriptions given by earlier Soviet and United States astronauts. Even before Gagarin's pioneer flight, photographs of the Earth had been obtained from unmanned rockets, and were clearly of great importance to geophysicists, geologists, and meteorologists, as well as to those engaged in pure space research. No photograph of the Earth as a complete globe has yet been obtained, since this would mean travelling out a distance much greater than a couple of hundred miles; but at least the curvature of the Earth's surface has been clearly shown on many pictures, together with the completely dark sky.

Cloud coverage is, of course, variable - but over wide areas it often obscures the surface detail completely. The absence of cloud over the Tibet region during the flight of Gordon Cooper, on 15-17 May 1963, led to some really spectacular pictures, taken with a hand-held camera through the transparent window of the space-craft, the fourth manned Mercury capsule. When the photographs were taken Cooper was moving at an altitude of over 100 miles above the Tibetan plateau.

Lakes show up with particular clarity, as dark patches - apart from the shallower ones, which were partly covered with ice. Some of the hills were also capped with ice and snow, and identi­fication presents no difficulty. Other photographs taken by Cooper showed the glaciers and snow-masses of the Himalayas, and have been of considerable value to map-makers and geologists. Ice floes drifting near the coast of north Russia have been recorded on photographs taken from the various Soviet space-craft, pre­sumably also with hand-held cameras; and it has been suggested that useful duties could be performed in ice patrolling. In any case, there can be no doubt about the value of the pictures sent back by the unmanned meteorological satellites of the American Tiros series, most of which are taken from 500 miles or so. On one of them, obtained from 400 miles, Great Britain is well shown; England and Wales are covered by 'fair-weather' cumu­lus clouds, and appear bright, since clouds are more reflective than clear ground. On this particular photograph Ireland seems to be covered with high cirrus cloud; a low-pressure system is approaching from the Atlantic, indicating the probability of bad weather in the near future.

Hurricanes and cyclones have also been photographed from the Tiros satellites, and the circulations of these systems - clock­wise in the southern hemisphere, anti-clockwise in the northern - have been evident. Violent storms of this sort have often been photographed in their early stages, so that people living in the danger zones have been given ample warning. There seems little doubt that a full-scale 'storm patrol' by means of satellites will be in operation within the next decade.

However, all the Earth photographs so far obtained have been taken from comparatively close range, and it is interesting to speculate about what our world would look like when seen from much greater distances. Seen from the Moon, the Earth would be magnificent indeed. Its light would be much more brilliant than full moonlight at home, partly because the Earth would appear considerably larger in the lunar sky and partly because it is a better reflector of sunlight. Its albedo, or reflecting power, has been estimated as almost 40 per cent, which compares very favourably with the 7 per cent of the Moon. Indeed, the Moon has an albedo lower than that of any other sizable body in the Solar System, with the possible exception of the remote planet Pluto.

Of course the Earth would show phases to a lunar observer. It would be full at midnight, and for protracted periods it would be a glorious object; the Moon rotates much more slowly than the Earth, so that a lunar night (that is to say, the time during which the Sun would be below the horizon) amounts to almost two of our weeks. At lunar noon the Earth would be new, and its dark side would be turned moonward. In point of fact, the Moon's rotation period is equal to its period of revolution around the Earth. This means that the Moon keeps virtually the same face turned towards the Earth, and the averted side remained unknown until a large part of it was photographed by the Russian rocket 'Lunik III' in October 1959. It also means that the Earth would seem to stay almost still in the lunar sky; it would not rise or set, and would always appear in virtually the same position, though it would admittedly oscillate slightly. From the averted hemisphere of the Moon, the Earth would never be seen at all, and the nights would be consequently much darker.

The Moon is only about a quarter of a million miles away, and the Earth would therefore appear as a relatively large object in the sky, but things would be very different for Mars, which never comes much within 35,000,000 miles of us. To a Martian observer, the Earth would show up as nothing more than a very brilliant 'star', probably bluish in hue. It would appear as an inferior planet, best seen in the west near sunset or in the east near sun­rise. This is how Venus actually appears to us, but there would be one important difference. Venus has no satellite; from Mars, our Moon would be a conspicuous object when seen with the naked eye. Telescopically, our hypothetical Martian would be able to see considerable detail on the Earth. The outlines of con­tinents and oceans would be obvious, and the variable cloud cover would be followed. Maps of Earth could be drawn up, though small details would naturally be lost.

Venus may approach us to within 25,000,000 miles, so that it comes considerably closer than Mars, but so far as we can tell the planet's cloudy atmosphere would preclude any visual obser­vations; even the Sun would not be seen, though its position would be indicated by the brightening of the sky. But for this, the Earth seen from Venus would be extremely brilliant, particularly as it would be a superior planet and would be visible against a really dark background.

From greater distances the Earth would fade rapidly into inconspicuousness. From Jupiter it would be hard to see at all, partly because of its smallness but mainly because it would keep very close to the Sun in the sky. And from Pluto, the outermost member of the Sun's family of planets, the Earth would be hope-lessly lost. Pluto moves at a mean distance of over 3,600,000,000 miles from the Sun, and would be a very poor site for carrying out observations of the other planets; only Neptune would be at all conspicuous. A hypothetical Plutonian astronomer would never be able to detect the Earth, and could have no knowledge of its existence. If this is so, then it would clearly be impossible to observe the Earth from the distance of even the nearest star, which lies at roughly 25 million million miles - over four light- years. No telescope of the sort that we ourselves could construct would be powerful enough, as a moment's consideration will show.

The Sun is a star, but by no means a particularly luminous one. It is average in size and luminosity, and only to its nearest stellar neighbours would it be at all conspicuous. Even Sirius, the brilliant star which is so prominent in our winter skies, is officially ranked as a dwarf even though it has twenty-six times the Sun's luminosity. It lies at a distance of eight and a half light-years, or roughly 50 million million miles; to a Sirian observer, the Sun would be invisible with the naked eye, and to detect the Earth, which is not only very small but is also inherently non-luminous, would be an obvious impossibility.

There is every reason to suppose that planetary systems are common in space, and there are a few cases of relatively nearby stars which seem to be attended by planetary bodies. The most interesting example is that of Barnard's Star, which is a red dwarf much less massive than the Sun. Here the companion seems to have only two and a half times the mass of Jupiter: this is much too low for a star, and so the body is presumably a planet, though we have no definite proof. Yet it is invisible, and it has been tracked down only because it produces minute irregularities in the motion of Barnard's Star itself. Were its mass as low as that of the Earth, it would cause no observable effects, and so it would remain unknown. In fact, we can never hope to detect Earth-like planets of other stars unless we can develop instruments very much more sensitive than those available to us at present.

Space research has made amazing progress during the last few years, and further spectacular developments may be expected in the near future, but we must always keep our sense of propor­tion. So far as rocketry is concerned, our range is limited; our Solar System is a very small part of the universe, and it would be misleading to suppose that it is of any real importance. To astro­nomers living in other planetary systems - if they exist, as surely they must - even the Sun will be obscure, and from a distance of only a few light-years the Earth will fade into total insignificance.

September 18 1964 - Vesta

Very little is heard about the minor planets, apart from the few whose exceptional orbits bring them relatively close to the Earth. Of these minia­ture worlds, the brightest, though not the largest, is Vesta; and this was the subject of our programme for September 1964.

One of the less-familiar members of the Solar System is now ex­cellently placed for observation in the evening sky. This is Vesta, the brightest of the swarm of asteroids or minor planets. It is far from spectacular, and even in large telescopes it appears as nothing more than a star-like point, but keen-sighted observers may be able to glimpse it without optical aid provided that they know exactly where to look for it.

Vesta is of the sixth magnitude, which means that from the viewpoint of the naked-eye observer it is hidden by the slightest trace of mist in the Earth's atmosphere; a dark, transparent sky is essential. Telescopically it looks exactly like a star, so that its nature is not evident at a glance. The only way to identify it with certainty is to observe the whole area from night to night; the stars will remain in the same relative positions, but the minor planet will move. This is brought out by Acfield's photograph. The date of the photograph itself was 8 September 1964, at 0.30 hours; the cross well to the right of Vesta shows the position of the minor planet in the early morning of 13 September. The five-day interval has been quite enough to reveal a decided shift.

Since Vesta is on the fringe of naked-eye visibility, even a very keen-sighted observer will be hard pressed to identify it without optical aid; binoculars, however, should suffice. Its faintness is by no means surprising in view of its small diameter and its con­siderable distance from Earth. Vesta is a mere 241 miles across, and moves round the Sun in a period of 3.6 years at a mean distance of 219,300,000 miles. A drawing showing Vesta and Eng­land to the same scale would demonstrate that we are indeed dealing with a dwarf world; yet only two of the minor planets - Ceres and Pallas - are larger.

The existence of at least one body moving in the region be­tween Mars and Jupiter was suspected long before the first asteroid was discovered. The Solar System is divided into two distinct parts. First come the four terrestrial planets (Mercury, Venus, the Earth, and Mars), after which there is a wide gap. Then follow the four giants (Jupiter, Saturn, Uranus, and Nep­tune) together with Pluto, a curious little world which may not be a true planet; according to some authorities, it is merely an ex-satellite of Neptune which has moved off in an independent path. A striking mathematical relationship, known as Bode's Law, led astronomers of the late eighteenth century to suppose that an extra planet might exist between Mars and Jupiter, and in 1801 the missing world war duly found. The Italian observer Piazzi, who discovered it, named it Ceres. It never attains naked-eye visibility, but with its diameter of 427 miles it remains the senior member of the asteroid swarm.

Further discoveries followed: Pallas in 1802, Juno in 1804, and Vesta in 1807. Number 5, Astrsea, came to light almost forty years later, due to the systematic labours of a German amateur named Hencke, and since 1847 no year has passed without the discovery of several new minor planets. Several thousands have now had their orbits worked out. On the other hand, very few are of appreciable size; most have diameters of under fifty miles, and the smaller members are probably not even approximately spherical.

Most asteroid discoveries have been made by means of photo­graphy. With a time-exposure, a star will appear as a sharp point, provided of course that the telescope is clock-driven to compensate for the east-to-west movement due to the rotation of the Earth; a minor planet will crawl across the sky, and will appear as a short trail on the photographic plate. Astronomers are not always glad to see these trails. Plates exposed for quite different reasons are often found to be crowded with asteroids, all of which have to be checked and eliminated. To make matters worse, some of the minor planets have high orbital inclinations - over 34 degrees in the case of Pallas, for example - so that they do not keep within the bounds of the Zodiac in the same way as the true planets. One infuriated observer referred to the asteroids as 'vermin of the skies'.

Most of the asteroids keep to the main zone between the paths of Mars and Jupiter, but some have eccentric orbits which carry them into other parts of the Solar System. No. 433, Eros - dis­covered in 1898 - may pass within 15,000,000 miles of the Earth ; No. 1566, Icarus, has a curious path which carries it closer to the Sun than Mercury, the innermost of the main planets, while No. 944, Hidalgo, swings out almost as far as the orbit of remote Saturn. In 1937 a dwarf body now known as Hermes approached the Earth to within 500,000 miles, and there were suggestions that it might even collide with our world. Such an event is most unlikely, but in any case Hermes can be little more than a mile in diameter, so that it could cause only local damage; it could certainly destroy a city, but it could not produce world-wide devastation.

Vesta appears the brightest of the minor planets because it is appreciably closer to the Sun and Earth than its two seniors, Ceres and Pallas. Even so, its distance from us is never as little as 100,000,000 miles, and to study details upon its surface is quite out of the question, even with the most powerful telescopes in existence. We can only speculate as to what it may be like, but we have at least a few concrete facts to guide us.

First, its small size means that it must have a very low escape velocity. The most important result of this is that it can retain no vestige of atmosphere, while its surface temperature must be very low indeed. No precise value for the escape velocity can be given, since we have no information about its density, but its gravita­tional pull is certainly very feeble. An astronaut who managed to land there would find that he would be able to jump an im­mense distance above the ground, and his subsequent descent would be extremely gradual. Yet it is not correct to say, as some writers have done, that a man could jump clear of Vesta by the power of his leg-muscles alone. This would not be possible except with an asteroid less than about two miles in diameter, assuming normal density; and Vesta, though small, is very much larger than that.

Probably, too, Vesta is more or less spherical, which means that its surface must be sharply curved; the 'horizon' would be strangely close. Minor variations in its light have led to the con­clusion that its rotation period is about 10 3/4 hours - slightly longer than the periods of either Ceres or Pallas, and three hours longer than that of Juno. This may indicate either that its shape is not entirely regular, or that some parts of its surface are more reflec­tive than others. _

When we come to consider the nature of the surface, we have to confess our complete ignorance, but Vesta seems to be a better reflector of sunlight than its companions. Its albedo, or reflecting power, has been estimated at 25 per cent as against 3 per cent for Ceres, 5 per cent for Pallas, and 11 per cent for Juno; the value for the Moon is considerably less than 10 per cent. Vesta, therefore, may have a smoother surface, but one cannot be sure, and moreover the albedo estimates - due to the German astronomer N. Richter - are bound to be somewhat arbitrary.

The origin of Vesta is similarly uncertain, but it was certainly formed in the same manner as the other members of the asteroid swarm. There are two main theories. It may be that the asteroids resulted from the break-up of an old planet or planets which used to move round the Sun between the orbits of Mars and Jupiter, in which case they are the visible remains of a tremendous out­burst which took place thousands of millions of years ago. Alter­natively, it has been supposed that the asteroids, together with meteoroids, were produced from material which was 'left over', so to speak, when the major planets were born.

The first of these theories is attractive, and has met with wide support, but it is not easy to see how a former planet could have met with disaster; a direct collision between two smaller bodies seems to be the only real possibility, and it is worth noting that the total mass of the asteroids is relatively small. There is no definite information as to the total number of members; R. S. Richardson, in the United States, has suggested 44,000, while Russian astronomers tend to believe that the true number may be as large as 100,000. Yet even if all the asteroids could be lumped together, the prove difficult to solve, and for the moment, at least, the nature of Vesta and its companions is not known.

It is worth noting, incidentally, that some of the smaller satellites _of the main planets may be captured asteroids. This applies to /Photos and Demos, the dwarf attendants of Mars, both of which appear to be less than a dozen miles in diameter, while the same may be true of the seven outer satellites of Jupiter and the smallest satellites of Saturn and Neptune. There is also a possibility that a second asteroid ring exists in the outer regions of the Solar System, though to observe small bodies at such a distance would be impossible with our present-day telescopes.

Science-fiction writers have put forward the idea that in the far future, when interplanetary travel has become commonplace, navigational beacons may be set up on Vesta and other asteroids. It would be rash to say that this will never be done, but at least it is not likely to be attempted for many centuries, even if it proves to be desirable! It is pointless to speculate about the pos­sibility of finding valuable minerals upon worlds such as Vesta, and we need spend no time upon another science-fiction idea, that of wrenching small asteroids free from their present orbits and steering them into more convenient paths to serve as natural space-stations. This remarkable scheme has been seriously dis­cussed by American scientists during the past few years, but it is quite impracticable. The energy needed to alter the path of an asteroid would be so great that there is no chance of anything of the sort being attempted.

If an astronaut could in fact go to Vesta, he would find him­self on a strange world. The temperature would be very low; there would be no atmosphere, and the Sun would appear relatively small and pale in the black sky. The constellation-patterns would of course seem the same as those we know, but there would be many additions to the sky, since Vesta lies within the main minor planet belt, and many of the other members of the swarm would appear as conspicuous naked-eye objects. From time to time, passing asteroids might even appear as distinct disks, and they would not add up to a body as massive as our Moon. The problem of the formation of the asteroids is likely to chances of collision certainly could not be ruled out. The pull of

gravity would be slight, though persistent; an Earthman would have very little weight.

There is one fact about which we may be quite positive: Vesta, like its companions, is utterly without life; no living organism of the kind known to us could survive under such conditions. In its way, Vesta is just as hostile as the Moon. Whether it will ever be reached seems extremely doubtful - and yet it is certainly not devoid of interest. If we knew how Vesta came into being, we should be well on the way toward solving the problem of the origin of the Solar System.

August 21 1964 - Colour in the Universe

During the television coverage of the ig6y lawn tennis championships at Wimbledon, the BBC started putting out programmes in colour. Of course, tests had been made much earlier, and colour television had begun in some countries ; but Wimbledon marked the start of a new era so far as Britain is concerned.

I can see that in the future, this change-over will cause some complica­tions in The Sky at Night programme. Colours in the sky are not strong, except with rare phenomena, and how they will show upon a television screen I do not know. However, it may be interesting to look back to a programme I devoted to this topic as long ago as the summer of 1964, when colour television still seemed to lie a long way in the future.

What is the colour of the night sky? Most people would probably answer this question by saying 'Black, with white stars' - but in fact the situation is not nearly so simple. There is plenty of colour in the universe, provided that the observer knows where to look for it. The planets, for instance, have their own distinctive hues, though only in the case of Mars is the colour really conspicuous to the naked eye.

Saturn, the outermost of the planets known in ancient times, is now visible in the south-east after sunset, and remains above the horizon all night. It has a dull, leaden aspect, and the astrolo­gers of past ages regarded its influence as baleful. It appears in the guise of a moderately bright star, lying well below the prominent Square of Pegasus; there should be no difficulty in finding it, since the only possible confusion is with the first-magnitude star Fomalhaut in Piscis Austrinus (the Southern Fish). Fomalhaut, however, is lower down and not so bright.*

Saturn, like the other three giant planets, is made up of gas, and this gas is known to be largely hydrogen. This means that the details on its surface are constantly changing, and it is im­possible to draw up permanent maps, though the main cloud belts have persisted since the start of serious telescopic observation. Spots are rare, but now and then something really spectacular is seen - the last occasion being in 1933, when W. T. Hay dis­covered a brilliant white spot near the planet's equator. Of course, Saturn is less easy to study than Jupiter, partly because it is smaller and partly because it is farther away. Its equatorial dia­meter is just over 75,000 miles, while at the date of opposition 24 August 1964) its distance from us was no less than 816,000,000 miles.

The general colour of Saturn's disk is yellow, as any small :telescope will show. During 1964 there were interesting changes there. For much of July the whole equatorial zone of the planet appeared to be tinged with brown or deeper yellow; I detected :his aspect on 9 July, and it has since seen confirmed by Ameri­can observers, while in Britain it has been recorded by A. W. Heath, Director of the Saturn Section of the British Astronomical Association. By mid-August the unusual hue was less pronounced, though it had not quite disappeared. The cause of this sort of phenomenon is not known.

The real glory of Saturn lies in its ring-system. The rings, made up of large numbers of small particles moving round the planet in the manner of dwarf moons, are of great extent, but are also very thin; their thickness can hardly be more than ten miles. The appearance of Saturn therefore changes markedly according to the angle at which the rings are placed with respect to the Earth. The rings are creamy, and are actually more brilliant than Saturn itself.

Jupiter, too, is predominantly yellow, but since 1959 its appearance has been unusual. Generally there are two distinct cloud belts, one to either side of the planet's equator, together - with other belts in higher latitudes. In 1959 the whole equatorial region turned an extraordinary orange or brownish hue; this persisted, with variations, until 1963, when the two equatorial belts had run together to form a continuous 'wedge of colour' right across the disk. It now seems that things are reverting to normal, and by August 1964 the separate belts were again identi­fiable. The remarkable feature known as the Great Red Spot has also been very much in evidence - and it really has been decidedly reddish in hue, though it has lost the brick-red colour which, from all accounts, it showed for a few years following 1878. It must be admitted that, so far, we have no real idea of the nature of the Great Red Spot, and neither do we know why Jupiter exhibits these peculiar changes in colour.

A small telescope will suffice to show the yellowness of Jupiter, together with the main belts and the four large satellites. Venus, which is a fine object in the eastern sky before dawn, is even more brilliant than Jupiter, but is less spectacular telescopically. It is a very different sort of world, since it is slightly smaller than the Earth, and is closer to the Sun than we are. Like the Moon, it shows phases, and at present it is 'gibbous', i.e., between half and full. Unfortunately no details are visible on its disk, since Venus is permanently covered with a dense, obscuring atmosphere which, according to recent results obtained from balloon-borne instruments sent up from the United States, con­tains a considerable amount of water vapour. Venus is slightly yellowish, though the naked-eye observer will probably call it pure white.

Through a powerful telescope, Mars is brilliantly coloured. Most of the surface is reddish-ochre, and is thought to be coated with some sort of mineral, possibly felsite or limonite. The polar caps, which are probably made up of some icy or frosty deposit, are glittering white, while the dark patches are said to have a greenish hue at times. H. Strughold has paid great attention to Mars, and has called it 'the Green and Red Planet', but to my eyes the dark markings generally seem grey. At any rate, it seems possible that they are due to living organisms, even though doubts have arisen lately.

Of the remaining planets, Mercury is somewhat pinkish, Uranus green, and Neptune bluish, while it has been claimed that Pluto is on the yellow side of white. However, these colours are not striking, and only experienced observers will be able to detect them. Mercury is always elusive; Uranus is on the fringe of naked-eye visibility, and both Neptune and Pluto are much too faint to be seen without optical aid.

In discussing the colours of the stars, it is natural to begin with our own particular star - the Sun - which, of course, is yellow. Its surface temperature is 6,000 degrees Centigrade, and it is in every way unremarkable. There are many similar stars in the Galaxy, and no doubt plenty of other stars are attended by in­habited planets. The only sensible way to observe the Sun telescopically is to project its image on to a white screen; to look straight at the Sun, even with a very small telescope, is extremely dangerous even when a dark filter is used. By projection, however, any sunspots which may be present are well seen. These spots appear dark, but this is an effect of contrast; if they could be seen shining by themselves they would be very brilliant, but they are less luminous than the rest of the Sun's surface because they are some 2,000 degrees cooler. During the summer of 1964 sun- spots were scarce, and there were long periods when the disk was completely blank. However, this was only to be expected; the Sun exhibits a roughly regular 'cycle' of eleven years, and from now on it is likely that spot-groups will become more frequent again. The next period of maximum activity is expected around 1969.

Stars which are hotter than the Sun will be white or bluish, while cooler stars will appear red. Binoculars are powerful enough to show these various colours well, while there are some stars whose hues are evident without any optical aid. A good example of this is Vega, in the small but interesting constellation of Lyra, the Lyre or Harp. Vega is extremely bright. It cannot match Venus or Jupiter, but of the so-called 'fixed stars' visible from Britain only Sirius is its obvious superior. Moreover, Vega is almost directly overhead during summer evenings, so that there should be no trouble in identifying it. It is definitely blue; it is fifty times as luminous as the Sun, and its distance from us is twenty-seven light-years, so that we are now seeing it as it used to be twenty-seven years ago.

The blueness indicates high temperature, and in fact the sur­face temperature of Vega is about twice as hot as the Sun. There is an interesting contrast with Arcturus, which now lies in the west, more or less in line with the curve of the 'tail' of the Great Bear. Arcturus shines about as brilliantly as Vega, and is actually twice as luminous, but its surface temperature is lower; only about 4,000 degrees. This means that its colour is a glorious orange. Vega is one of three first-magnitude stars making up what is unofficially termed the 'Summer Triangle'. The other two members are Deneb in Gygnus (the Swan), which is yellowish and Altair in Aquila (the Eagle), which is pure white. Deneb, apparently the faintest of the three, has been found to be a re­markably luminous supergiant, equal to at least 10,000 Suns and lying at a tremendous distance from us.

The best example of the Red Giant star is, undoubtedly, Betelgeux in Orion. Orion is a winter constellation, but now rises before dawn, and the contrast between its two leading stars is very marked; the redness of Betelgeux is as obvious as the pure white light of Rigel. Another Red Giant is Aldebaran in Taurus (the Bull), which lies in line with the three stars of Orion's belt, and is associated with the V-shaped cluster of stars known as the Hyades.

With the naked eye, only a few of the brightest stars are strongly coloured; with fainter objects, optical aid is needed before the hues can be well seen. A good example of this is Herschel's 'Garnet Star', Mu Cephei, not very far from Polaris. To the naked eye it appears unremarkable, but any small telescope makes it look like a tiny glowing coal. The surface temperature in this case is only about 3,000 degrees.

Observers who have access to binoculars or small telescopes will find it interesting to look from star to star and note the various colours; it will not take more than a few minutes to find that the stars are utterly unlike each other. There are lovely colours, too, among double stars, of which Albireo in Gygnus is an outstanding example. Albireo is the faintest of the five stars making up the •.veil-known cross of Gygnus, and to the naked eye it seems white, but a telescope will show that it is made up of a golden-yellow primary together with a much fainter companion which some people term green and others blue. And there are bright red stars, such as Antares in Scorpio (the Scorpion) which have green com­panions. The greenness of the small attendant of Antares is accentuated by contrast, but this does not make it any the less beautiful.

Not all double stars show contrasting colours. Look, for instance, at Epsilon Lyra:, which lies close to Vega. Keen-sighted observers will note that it is made up of two; a 3-inch refractor will show that each component is again divided, so that Epsilon Lyra; is a double-double or quadruple system. All four of its suns are white.

Very faint stellar objects show colours which cannot be de­tected except by photography. There is a good example of this in Messier 57, the Ring Nebula in Lyra, which also lies near Vega. The Ring is a 'planetary nebula', but the name is a bad one, since planetary nebulae are neither planets nor nebulae. Messier 57 consist of a faint central star surrounded by a tremendous en­velope of tenuous gas, so that it looks rather like a very dim, luminous bicycle-tyre. Moderate telescopes will show it clearly, and it is easy to find, but no colour will be detected. A famous photograph taken some years ago with the largest telescope in the world, the Palomar 200-inch reflector, showed that the Ring has a bluish central area with the outer parts yellowish and red.

Star-colours are important because they provide a key to the surface temperatures, though detailed analysis is carried out with the aid of spectroscopic equipment rather than by visual estima­tion. Yet the colours are spectacular, too, so that the casual ob­server who uses binoculars to look at the orange Arcturus, the glittering blue Vega, and the dull yellow planet Saturn can hardly fail to be impressed. We live in a coloured universe; the skies are anything but drab.

June 26 1964 - Astronomy Old and New

Astronomy is a fast-developing science; it has altered more in the past hundred years than it did in the previous thousand. But despite the modern emphasis upon vast telescopes, refined photographic techniques and space probes, it is always worth while to pause for a moment and look back at some of the ideas current in past ages. This was what we did for the July 1964 programme, in which I was joined by Henry Brinton. Following it, I had some amusing letters.

There is one point that should be made. During the programme, I ex­pressed serious doubts about Professor Hawkins' theory that Stonehenge is an ancient computer. My viewpoint was that people who possessed enough knowledge to build anything of the sort would not need to do so; they could manage excellently by calculations, without going to the trouble of constructing a huge monument. Since then, the evidence seems to indicate that Professor Hawkins was right and that I was wrong, so that I hereby retract my scepticism even though I have not altered the article as it appeared in 1964.

Astronomy is the oldest science in the world. The earliest men must have looked up at the heavens and wondered at what they saw there; it was not until later that the pseudo-science of astrology arrived upon the scene to confuse men's minds and hold up progress.

Observational records of celestial phenomena go back for thousands of years. For instance, the ancient Chinese observed eclipses of the Sun and Moon, although they did not know why an eclipse occurs and they would have found it impossible to believe that the Earth is a planet moving round the Sun. At the time of a solar eclipse, the Chinese believed the Sun to be in danger of being eaten by a dragon, so that they used to bang pots and pans and make as much noise as possible in order to scare the dragon away.

Solar eclipses, caused when the Moon passes between the Earth and the Sun, are indeed highly spectacular. When the Moon passes into the Earth's shadow, at a lunar eclipse, the usual result is to make the Moon turn a dim and somewhat coppery colour. The only light reaching the lunar surface during the total phase of the eclipse has been refracted through the Earth's atmosphere, and it is obvious that the state of the atmosphere will affect the look of the eclipsed Moon. Quantities of volcanic dust in the upper air will produce a 'dark' eclipse, such as seen in 1816, following the Tamboro eruption of the previous year; the eclipses following the eruptions from Krakatoa (1883), Katmai (1912), and Mount Agung, on Bali in the East Indies (December 1963), were also very dark.

There is strong evidence that a lunar eclipse was recorded by the Chinese as long ago as 1136 b.c. The Greeks, however, were the first to raise astronomy to the level of a true science, because they did their best to interpret their observations; by using the so-called Saros Period, they were able to predict eclipses with fair accuracy. Thales of Miletus, the earliest of the great Greek philosophers, knew that any solar or lunar eclipse will be followed by a similar eclipse 18 years 10J days later; the relationship is only approximate, but for lunar eclipses, in particular, it works quite well. By 450 b.c. another Greek, Anaxagoras of Clazomenaj, was able to explain the cause of an eclipse of the Moon, and to state that because the Earth's shadow was curved, the Earth itself must be spherical.

Recently, Professor Gerald Hawkins, of Harvard, has suggested that the early Britons, too, were able to predict eclipses. Accord­ing to Hawkins, Stonehenge is nothing more than a primitive computer, the outer circle of fifty-six pits being used as a form of protractor. For instance, eclipses are likely to occur when, to an observer standing in the centre of the monument, the mid-winter Moon rises over the large block known as the Heel Stone.

This fascinating that it may be regarded as a form of observatory as well as a lemple. Midsummer ceremonies are always associated with it, and it is also popularly linked with the ancient Druids. In point of fact, the monument existed long before the Druids were active in England, and there is no evidence that the Druids ever used it, while there is a great deal of indirect evidence that they did not. The same applies to the other stone circles found all over Britain - at Roll right in Oxfordshire, for instance, and Callanish on the Island of Lewis. G. Henderson considers that they could be used as 'star markers' to check the march of the seasons, and this is certainly possible, since the observations themselves would be very simple and straightforward.*

Undoubtedly the old star-gazers were skilled at what may be termed positional astronomy; Egyptian observations, for instance, were very precise, and the later Greeks drew up remarkably good star catalogues. Subsequently, however, some strange theories were put forward. One of the most curious relates to the Egyptian pyramids, with special reference to the Great Pyramid of Khufu. Here again there is no doubt about the astronomical alignment. This is related to the north celestial pole, now marked by Polaris to within one degree, but in Egyptian times situated near the much fainter star Thuban in Draco; the slow shift is due to the phenomenon of precession, or change in direction of the Earth's axis.

The great pyramid

In 1859 John Taylor, an eccentric London publisher, issued a book called The Great Pyramid.: Why was it Built? And Who Built it? Taylor never visited the pyramid, but he believed that he had found various mathematical truths in its measurements which showed him that the Egyptian priests knew most, if not all, of the secrets of the universe, but had prudently decided to keep these truths to themselves. Taylor was, therefore, the founder of the cult of pyramidology, but his speculations would soon have been forgotten but for the fact that he found a strong supporter in Charles Piazzi Smyth, Astronomer Royal for Scotland. Smyth's theory may or may not be correct, but in any case Stonehenge has certainly an astronomical significance, so subsequent book, Our Inheritance in the Great Pyramid, is a classic of crank science.

Smyth began by taking Taylor's discovery that if you divide the height of the monument into twice the side of a base, you obtain a fairly close approximation to the value of pi (the ratio of diameter to circumference of a circle). The square of the height, moreover, is equal to the area of one face of the pyramid. On these and other similar grounds Smyth claimed that the Egyptians were able to 'square the circle'. By juggling with the length of the diagonals, he also considered that he had proved that the pyramid builders had worked out an exact figure for the preces­sion of the equinoxes - the movement of the celestial Pole which revolves once in about 26,000 years. From this Smyth went on by ingenious but rather arbitrary calculations to derive the unit of measure which the builders used. This he believed to be a little more than two feet, and he associated the unit with the cubit of the Bible. He then divided the cubit into twenty-five 'pyramid inches', which were very slightly different from the English inch. Smyth attributed the discrepancy to carelessness on the part of later artisans. This, of course, proved that the pyramid inch was sacred, and in 1879, in Boston, U.S.A., a movement was started for outlawing the 'atheist' metric system. The movement actually had the moral support of President James Garfield.

The possibilities are endless. For instance, the number of pyramid inches in the height of the pyramid, multiplied by a thousand million, yields 91,840,000 miles, which was close enough to the Earth's distance from the Sun (rather less than 93 million miles, on the average) to make Smyth sure that he had found another sacred relationship. But it was in connection with the pyramid's internal passageways that Smyth rose to his greatest heights. When these passages are measured in pyramid inches, counting one inch to the year, and the symbolism is properly interpreted, then - said Smyth - the principal dates in the Earth's past and future are plainly indicated. These include the creation of the world in 4004 b.c., the birth of Christ and of course the end of the world, which has been predicted so often in so many different ways.

When many measures are available, a dextrous mathemati­cian - as Smyth was - can make a judicious selection to prove almost anything. It was a great pity that Smyth himself, who made many valuable contributions to astronomy, should have become a convert to eccentricity of this sort; it damaged his reputation, and also led to a positive craze for pyramidology which lingers on even today. It is perfectly harmless, but it can hardly be re­garded as scientific. Sir Flinders Petrie, the great archaeologist, once caught a fervent pyramidologist filing down a projecting stone to make it conform with his theories.

One feels that the builders of the pyramids were rather more logical than some of the nineteenth-century theorists. Yet the Egyptians made little effort to interpret their astronomical ob­servations; this was left to the Greeks, who made amazing pro­gress in all fields of physical science. Had they realized that the Earth moves round the Sun, instead of lying at rest in the centre of the universe, astronomy would have developed quickly. A few of the Greek philosophers (Aristarchus, for example) did take this vital step, but met with little support, and the reality of the Earth's movement round the Sun was not properly demonstrated until about 400 years ago.

On the other hand, the Greeks knew that the Earth is a globe. The form of the shadow on the eclipsed Moon was only one of their many proofs. For instance, ships disappear below the horizon when sailing out to sea, which would be impossible on a flat Earth. And Aristotle, in about 350 b.c., pointed out that the stars appear to alter in height above the horizon according to the observer's position on Earth; Canopus, a brilliant southern star, can be seen from Egypt, but never from Greece. This is easy to explain on the assumption that the Earth is a globe, but cannot be accounted for by supposing the Earth to be flat. Moreover, yet another Greek scientist, Eratosthenes, measured the circum­ference of the globe with remarkable accuracy. The value which he obtained was much better than that used by Christopher Columbus on his pioneer voyage so many centuries later.

It is rather surprising, then, to find that even in the modern age there are still some people who doubt the spherical form of the Earth. The International Flat Earth Society flourished up to a year or two ago, and issued pamphlets as well as holding meetings. Their 'proofs' were fascinating, though hardly con­vincing. They pointed out, for instance, that a time-exposure of the night sky will produce a photograph showing star trails, which are hard, sharp lines. Astronomers attribute this to the rotation of the globe. The Flat Earthers, however, considered that the sharpness of the trails showed the world to be stationary - otherwise the trails would have been blurred. And in the town of Zion, Illinois, on the shores of Lake Michigan, may be found the remnants of a religious sect known as the Christian Apostolic Church, founded in 1895 and ruled for thirty years by Wilbur Glenn Voliva, who regarded the Earth as flat, with the North Pole in the centre and the South Pole distributed round the circumference. Voliva held that a huge wall of ice and snow prevented ships from sailing off the edge and tumbling into Hades. He added, as an aside, that the Sun was a mere 32 miles across, and not more than 3,000 miles away.

Other theories have been put forward. In 1818, an American officer, Captain John Cleves Symmes, claimed that the Earth was made up of five concentric spheres, with openings several thousand miles in diameter at the poles; sea flowed through both polar openings, and plant and animal life abounded on the con­cave interior as well as on the convex surface of the next sphere. Later, he petitioned Congress to finance a trip to the North Pole in order to check his theory. Congress did not agree, though it must be recorded that on the second petition Symmes found twenty-five supporters.

Perhaps the strangest theorists of all are those who maintain that the Earth is the inside of a hollow globe, with the Sun in the middle of the structure and Australia above our heads, and then he obtained was much better than that used by Christopher Columbus on his pioneer voyage so many centuries later.

It is rather surprising, then, to find that even in the modern age there are still some people who doubt the spherical form of the Earth. The International Flat Earth Society flourished up to a year or two ago, and issued pamphlets as well as holding meetings. Their 'proofs' were fascinating, though hardly con­vincing. They pointed out, for instance, that a time-exposure of the night sky will produce a photograph showing star trails, which are hard, sharp lines. Astronomers attribute this to the rotation of the globe. The Flat Earthers, however, considered that the sharpness of the trails showed the world to be stationary - otherwise the trails would have been blurred. And in the town of Zion, Illinois, on the shores of Lake Michigan, may be found the remnants of a religious sect known as the Christian Apostolic Church, founded in 1895 and ruled for thirty years by Wilbur Glenn Voliva, who regarded the Earth as flat, with the North Pole in the centre and the South Pole distributed round the circumference. Voliva held that a huge wall of ice and snow prevented ships from sailing off the edge and tumbling into Hades. He added, as an aside, that the Sun was a mere 32 miles across, and not more than 3,000 miles away.

Other theories have been put forward. In 1818, an American officer, Captain John Cleves Symmes, claimed that the Earth was made up of five concentric spheres, with openings several thousand miles in diameter at the poles; sea flowed through both polar openings, and plant and animal life abounded on the con­cave interior as well as on the convex surface of the next sphere. Later, he petitioned Congress to finance a trip to the North Pole in order to check his theory. Congress did not agree, though it must be recorded that on the second petition Symmes found twenty-five supporters.

Perhaps the strangest theorists of all are those who maintain that the Earth is the inside of a hollow globe, with the Sun in the middle of the structure and Australia above our heads, and the Earth itself extending infinitely in all directions. This is still the view of a German society, and in 1933, at Magdeburg, a rocket was sent up to test the hypothesis, the idea being that if the ascent were vertical the rocket would inevitably crash-land in the Antipodes. The first rocket rose to a height of six feet and ex­ploded ; the second vehicle was launched horizontally instead of vertically, and after that the experimenters ran out of money.

There are many other eccentric theories which would have seemed strange even to our ancestors. Dr Velikovsky, Russian- born but now resident in the U.S.A., has published some large books in which he claims that the planet Venus is an ancient comet (!) which once stopped the Earth's rotation for a while, causing the Red Sea to divide precisely at the time when the Children of Israel wanted to cross it. The universal ice theory of Hans Horbiger, who regarded the Milky Way as being composed of ice blocks which periodically hit the Sun and produced sun- spots, became so popular in Nazi Germany that the Propaganda Ministry actually had to issue a statement that it was possible to be a good National Socialist without believing in Horbiger's doctrines. The cult spread to Britain, mainly through the writings of H. S. Bellamy, and still exists. Finally, there is astrology, which retains a considerable following even though it has long since been shown to be as baseless as pyramidology or universal ice.

Most of these strange ideas are innocuous enough, and they have their amusing side - yet their continued existence shows that we cannot afford to laugh at the understandable mistakes made by theorists of long ago. Moreover, there is every prospect that the astronomers of, say, a.d. 3000 will look back at us in the same light as we ourselves regard the early star-gazers who be­lieved the Earth to be the centre of all things.

Author's Preface to Book 1 & Video Interview from 2000

(C) Journeyman Pictures

In April 1957 BBC Television invited me to present a series of astronomical programmes under the general title of The Sky at Night. Some time later, Mr Maurice Ashley, Editor of The Listener, invited me to contribute articles on the same theme, based entirely on the programmes, though not verbatim reports (which would have been impossible in any case, since I never use a script when I am 'on the air'; I cannot broadcast that way). It has now been decided to issue some of these in book form, but I feel that one thing should be made clear at the outset: the articles have been published before - the dates are given - and so are not new contributions. Moreover, there is a certain inevitable overlap with other books that I have written. I have done my best to select the articles in which overlap is cut to a minimum, but I would not wish anyone to buy the present book under a false impression!

At this point I should express my sincere thanks to Mr Ashley; it has always been a pleasure to write for The Listener.

The method adopted here has been to reproduce the articles in the original form, though in one or two cases I have added foot­notes to bring them fully up to date, and there are a couple of instances in which I have made deletions so as to avoid including anything which has now been superseded. The articles have been arranged in chronological order, which seemed to be the best way. It is very pleasant to think that the articles have caused sufficient interest to warrant their being issued in a book, and I am most grateful to all those who have given me help in both the television programmes and in the present production.

PATRICK MOORE

East Grinstead August 1964

August 8 1964 - Close-Up of the Moon

This last article — written after the rest of the book had gone to press — differs from the others inasmuch as it has not been published before. When the U.S. rocket Ranger VII was dispatched toward the Moon on 28 July 1964, there was considerable excitement everywhere, plus a general feeling that this time the programme of taking lunar photographs from close range would be carried through successfully. I made a fleeting appearance on television after News Extra on 29 July, and said that in my view the interesting problems likely to be solved were (1} whether the lunar seas were in fact deep dust-drifts, and (2) whether there were many small craterlets too tiny to be seen from Earth. I also said that I had the most serious doubts about the existence of dust, and that I expected large numbers of minor craterlets.

The landing-point of Ranger VII was known, and when it duly hit the Moon on 31 July, after having sent back more than 4,000 photographs, it was clear that we would have to present a Sky at Night ''special'. This was duly broadcast after the end of normal programme time. I was joined by Peter Stewart, the rocket expert, and we tried to call up the Jet Pro­pulsion Laboratories in Pasadena, California. Unfortunately we were unable to establish two-way communication. I could hear Pasadena, Pasa­dena could hear the control centre in London, and control centre could hear both of us, but that was all. Finally, some thirty seconds before trans­mission was due to begin, I rapped out a series of questions which were repeated from control centre and answered by Pasadena.

Half a dozen of the Ranger VII pictures had been sent across to us, so that we were able to put them on the screen less than twelve hours after they had been taken. It was all most interesting, and quite different from our abortive effort with Lunik IV over a year earlier! On that occasion (April 1963) we undertook a similar Sky at Night special as the Soviet probe, launched on 2 April, neared the Moon. The general consensus of opinion was that the Lunik would either make a 'soft landing' or else deposit a package of some kind on to the Moon. During the vital period I carried out a live transmission from Lime Grove; I had a telephone link with Moscow, a radio link with Jodrell Bank (where Colin Ronan was stationed, and where Professor Sir Bernard Lovell generously gave up some of his time to join in), and cameras fixed to the large telescopes at Edinburgh (with Dr Peter Fellgett commenting) and Patcham (where George Hole was in readiness). The idea was to get the latest news from Moscow, listen to the signals from Jodrell Bank, and observe the impact from Edinburgh and Patcham. What actually happened was that nobody in Moscow seemed to know anything, Jodrell Bank could not hear anything, it was raining in Edinburgh and cloudy at Patcham, and in any case Lunik IV missed the Moon by four thousand miles. The programme provided a perfect instance of the workings of Spode's Law.

At 13 hours 25 minutes on 31 July 1964 - that is to say, at 2.25 p.m. British Summer Time - the American rocket Ranger VII hit the Moon. For the previous quarter of an hour it had been transmitting pictures of the lunar surface taken from close range, and when the first photographs became available they proved to be of amazingly good quality. Features much too small to be visible from Earth were clearly shown, and several outstanding problems of the Moon were cleared up at once.

The success of Ranger VII ended almost six years of frustrating failure by the American scientists. The moon-shot programme had been started as long ago as 1958, but it had been dogged by ill-fortune from the outset, and the plan of setting a man on the lunar surface before the end of 1970 had begun to look very over- optimistic. Now, perhaps, the tide had turned.

The first United States moon-rockets were the Pioneers. Five were launched between 17 August 1958 and 3 March 1959, but with somewhat depressing results. The original vehicle reached i2i miles, but then its lower stage exploded and the flight came to a premature end. The next rocket, officially known as Pioneer I, was sent up on October 11 and reached an altitude of slightly over 70,000 miles, but then fell back to Earth and burned up in the atmosphere (at least, this was presumably its fate; no trace of it was ever found). Pioneer III, launched on 9 November, was a total failure, since its third stage failed to ignite, while the fourth attempt, made on 6 December, attained 66,200 miles before it too fell back. The last Pioneer, No. 4, went up on 3 March of the following year; it weighed 13 lb and passed within 37,000 miles of the Moon during the night of 4-5 March. Signals from it continued to be received until it had receded to some 400,000 miles and had entered an orbit round the Sun, so becoming a tiny artificial planet. That, for the moment, ended the series, but meanwhile the Russians had been far from idle; during 1959 they launched their three celebrated Luniks, the second of which landed on the Moon, while the third went on a 'round trip' and sent back photographs of the area of the lunar surface always turned away from Earth.

It was not until 1961 that the Americans were ready to try again. The Ranger programme was initiated on 23 August, but the first two vehicles failed to go anywhere near the Moon. Ranger III, launched on 26 January 1962, seemed much more promising, and for a while hopes ran high; it looked as though the attempt to photograph the Moon from close quarters would be crowned with success. Unfortunately, errors then became apparent. The first stage of the launcher, an Atlas rocket, had been slightly too effective, so that the vehicle moved at more than its planned velocity and never approached the Moon to within less than 23,000 miles. Even so, it was still hoped that photographs would be received, and Ranger III was positioned by remote control, but the ill-luck was still there; further faults developed, so that only the extreme edges of the television pictures could be picked up, showing no details whatsoever.

The story was continued in April, with Ranger IV. The vehicle is thought to have reached the Moon on 26 April, but this time the photographic equipment failed as well as the guidance system, so that no data of any sort were obtained. Ranger V, of 18 October, was even less successful; it missed the Moon by a wide margin, and contact with it was lost at a relatively early stage.

The next attempt came from Russia. On 2 April 1963 the Soviet space-researchers launched Lunik IV, which was said to weigh over 1 1/4 tons and to carry complex equipment. Very few details about it were released, and even now nobody outside the USSR scientific circle seems to know just what it was meant to do. In the event, it merely went past the Moon and continued its journey into space, so that it was clearly a failure.

When 1964 opened, the situation appeared somewhat depress­ing; all in all, very little obvious progress had been made for four years so far as moon-shots were concerned. I think that the news of the launching of Ranger VI, on 29 January, was received with resigned pessimism - and the fears were justified. At least the Americans brought the vehicle down exactly where they had hoped, in the Mare Tranquillitatis, but the photographic equip­ment failed completely. Neither has any trace of an impact-scar been detected, though the exact position of the landing is known.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Photographs of the Moon taken from Ranger VII

Left: The moon from 34 miles the area covered is 16 miles square. Right the Moon from 3 miles; takes 3.2 seconds before Ranger VII hit the Moon.

With the ascent of Ranger VII, on 28 July, the total bill for the American lunar programme passed the £90,000,000 mark, and so far there had been remarkably little to show for it. Yet somehow or other there was a feeling that the new launching would be different - and so it proved.

Ranger VII took 67 hours 35 minutes to complete its journey of 243,665 miles. There were no communication troubles; the probe was tracked from America and also from Jodrell Bank, though the last stages of the flight could not be followed from Britain because the Moon had dropped below the horizon. When the vehicle was some 1,300 miles above the lunar surface, the cameras were turned on, and for the next 16minutes worked perfectly; 4,316 pictures were received, the last of which was still being transmitted when Ranger VII smashed itself to pieces on the Sea of Clouds.

There have been reports that on this occasion the impact was actually observed. Astronomers at Gape Kennedy, using power­ful equipment, described a small black speck about twenty seconds after the crash-landing; this speck mushroomed into a small white cloud 'resembling a three-leaf clover', which rapidly diffused and disappeared. The reports are not conclusive, but they are at least plausible. Whether any permanent scar will be detected seems rather doubtful. If it is visible at all, a giant telescope will be needed to show it.

Before going into further details about the photographs them­selves, it is important to say something about their purpose. It would be pointless to spend over £90m. in doing no more than show fine details on the Moon unless they would add materially to our knowledge of the lunar world, but in fact there were several urgent problems which could not be solved in any other way. The main question concerned the nature of the surface layer.

In 1955 a revolutionary paper had been published by T. Gold, well known for his work in helping to formulate the steady-state theory of the universe. According to Gold, the lunar craters were produced by meteoritic bombardment, while the maria were filled with dust - so that any astronaut unwise enough to land there would be comprehensively swallowed up in a dust-ocean more treacherous than any quicksand. Practical lunar observers were, in general, unimpressed,* but the theory could not be rejected out of hand, and it had to be checked before the more ambitious programmes, involving manned craft, could be worked out in every detail.

Another point concerned the numbers of very small craters scattered over the Moon. From Earth, it is difficult to see any crater with a diameter of less than 1,600 feet or so; in fact, we can examine only the coarser details. It was essential to find out whether any truly level ground existed, or whether the surface were pitted even in those regions which seem smooth and mirror like in Earth-based telescopes. For this reason, Ranger VII was aimed at a mare-surface rather than a bright upland area. It came down in the Mare Nubium, in the general neighbourhood of the low-walled, 36-mile crater Guericke - and the aiming was incredibly precise. A mid-course correction was made, on schedule, but no terminal correction was necessary.

Of the first pictures to be made available, two were particu­larly informative. From an altitude of 3 miles, 3.2 seconds before impact, craters less than a dozen feet across are shown; the last picture, still being transmitted at the moment of landing, covers an area comparable with that of a tennis-court, with craters 3 feet across and a mere 12 inches or so deep. These tiny objects are sharp and clear-cut, which would be out of the question in a surface of soft dust. Moreover, it was stated that some of the other photographs showed rather larger craters (that is to say, over 100 feet in diameter) containing isolated rocks which had been presumably hurled out during the formation of still larger craters — and yet were obviously not dust-covered. In fact, Gold's whole idea was wrong. Any dusty or ashy layer on the Moon could hardly be more than a few inches deep, so that basically the surface would be strong enough to bear the weight of a landing vehicle, even if unsafe areas existed here and there.

Associated with the dust problem was the old, much-discussed argument about meteors versus volcanism as the main force in crater production. Gold had been a strong supporter of the impact theory, and so had many other professional astronomers, such as G. P. Kuiper, H. Urey and F. Hoyle. Urey had even stated that the evidence was so overwhelming that there was no need to talk about it further. Others were not so sure, and at the New York lunar conference held in May 1964, at which I read a paper, I found that the meteor idea had come under heavy fire from geologists as well as practical lunar observers. For instance, J. Green of the United States and G. J. H. McCall of Australia drew attention to a possible analogy between lunar craters and terrestrial volcanic calderas. My own views were quite clear-cut; as I said at the conference, I have always been an 'unrepentant vulcanist', though no doubt numerous small meteor pits exist.

It cannot be said that the Ranger VII pictures give a final answer, but it looks very much as though vulcanism has, after all, been the main factor. At any rate, there can be no doubt that the Moon has been the site of tremendous volcanic activity at some stage in its history. Many of the minor pits in the area where Ranger landed may well be due to impact - but in all probability the bodies producing the pits were hurled out from lunar craters of greater size instead of coming from space.

One photograph, taken from a height of 34 miles, showed what Kuiper called 'a whole nest' of small craters, some of them no more than 15 feet in diameter, said to have rounded crests potentially dangerous to astronauts. This particular area was crossed by one of the bright rays from the 56-mile crater Coper­nicus, and it was evident that some connection existed between the craterlets and the ray, so that the craterlets looked as though they must be secondary pits due to the eruption of Copernicus itself. As for the rays, it was claimed that they were sizeable rocks thrown off during the production of the focal craters - but to me this idea does not seem to be at all convincing, and the rays remain enigmatical.

Moreover, there is at least a chance that some of the rays shown in the photographs do not come from Copernicus at all, but from Tycho. Of course, Tycho, in the southern uplands of the Moon, is a long way from the point where Ranger VII landed — but the Tycho ray-system is more extensive than that of Copernicus and the alignment seems to fit the general Tycho pattern well. Further studies of the photographs will certainly clear up this and other points. Meanwhile, Ranger VII has at least disproved the dust-drift theory, and it now seems likely that the mare surfaces are made up of some material such as hardened lava.

Of course, only a very limited part of the Moon was covered; even the first pictures, taken about i6| minutes before impact, showed an area of no more than 180,000 square miles, appreciably less than that of France. Really level ground was lacking, and it does not seem probable that other mare-surfaces are much smoother; astronauts of the future cannot hope to find any mirror-like expanses big enough to be pressed into service as landing-grounds.

It cannot be said that the photographs have provided any major shocks for those astronomers who have always disbelieved in Gold's dust theory, and who have regarded the lunar surface as essentially volcanic in character. However, it has been pointed out that there seem to be few small cracks or fissures. Fissures of such a kind may be absent, or else they may simply not have shown up; this is a problem for the future, but since there are so many crater-chains, clefts and valleys on a larger scale, it would be distinctly strange to find that small cracks do not exist.

There is one more point which has already been brought up, though not by the American scientists concerned in the experi­ment. It has long been thought that the Moon is utterly without life; even lowly vegetation is improbable to the highest degree. The Ranger photographs have shown nothing that could be interpreted as being due to living organisms, and nobody had had the slightest expectation that they would. The Moon is a sterile world, and probably has always been so.

The success of Ranger VII means that plans for the future can be continued with high hopes. Two more vehicles of the same sort are planned for early 1965; Ranger VIII will go up in January, all being well, and Ranger IX will follow in February. No major modifications to the probes or launchers are expected, but different areas of the Moon will come under study, and it may well be that one of the rockets will be aimed at a bright upland instead of a dark plain. I rather hope that one Ranger will land near Aristarchus, the brilliant crater near which observers at the Lowell Observatory, Flagstaff, reported red patches in October and November of 1963.

This will complete the Ranger series. Next will come vehicles of the Surveyor type, involving soft landings, and 1966 should see the launching of Orbiter vehicles, which will go round the Moon taking high-resolution photographs from heights of 30 miles or so. Whether the Americans will manage a manned flight to the Moon before 1970 remains to be seen. Incidentally, we must not forget the Russians, who have had no real successes with their lunar or planetary probes since 1959, but who are certainly making plans of their own. A soft landing on the Moon by a Soviet space-craft may be imminent.

At present Ranger VII lies wrecked in the Mare Nubium, but I doubt whether it will stay there for ever. At some future date an expedition from Earth will surely collect its shattered remnants and carry them off to a museum. America's lunar probe accom­plished its task more brilliantly than its makers can have dared to hope, and it has certainly earned its place in history.