The Other Side of the Sky

by Arthur C. Clarke

  Geophysics, as I have mentioned, was Dr Paynter’s real business; diamonds were merely a side line. He had developed many remarkable surveying instruments which could probe the interior of the Earth by means of electric impulses and magnetic waves, so giving a kind of X-ray picture of the hidden strata far below. It was hardly surprising, therefore, that he was one of the men chosen to pry into the mysterious interior of the moon.

  He was quite eager to go, but it seemed to Commander Vandenburg that he was relucant to leave Earth at this particular moment. A number of men had shown such symptoms; sometimes they were due to fears that could not be eradicated, and an otherwise promising man had to be left behind. In Paynter’s case, however, the reluctance was quite impersonal. He was in the middle of a big experiment – something he had been working on all his life – and he didn’t want to leave Earth until it was finished. However, the first lunar expedition could not wait for him, so he had to leave his project in the hands of his assistants. He was continually exchanging cryptic radio messages with them, to the great annoyance of the signals section of Space Station Three.

  In the wonder of a new world waiting to be explored, Paynter soon forgot his earthly preoccupations. He would dash hither and yon over the lunar landscape on one of the neat little electric scooters the Americans had brought with them, carrying seismographs, magnetometers, gravity meters, and all the other esoteric tools of the geophysicist’s trade. He was trying to learn, in a few weeks, what it had taken men hundreds of years to discover about their own planet. It was true that he had only a small sample of the moon’s fourteen million square miles of territory to explore, but he intended to make a thorough job of it.

  From time to time he continued to get messages from his colleagues back on Earth, as well as brief but affectionate signals from Mrs P. Neither seemed to interest him very much; even when you are not so busy that you hardly have time to sleep, a quarter of a million miles puts most of your personal affairs in a different perspective. I think that on the moon Dr Paynter was really happy for the first time in his life; if so, he was not the only one.

  Not far from our base there was a rather fine crater pit, a great blowhole in the lunar surface almost two miles from rim to rim. Though it was fairly close at hand, it was outside the normal area of our joint operations, and we had been on the moon for six weeks before Paynter led a party of three men off in one of the baby tractors to have a look at it. They disappeared from radio range over the edge of the moon, but we weren’t worried about that because if they ran into trouble they could always call Earth and get any message relayed back to us.

  Paynter and his men were gone forty-eight hours, which is about the maximum for continuous working on the moon, even with booster drugs. At first their little expedition was quite uneventful and therefore quite unexciting; everything went according to plan. They reached the crater, inflated their pressurised igloo and unpacked their stores, took their instrument readings, and then set up a portable drill to get core samples. It was while he was waiting for the drill to bring him up a nice section of the moon that Paynter made his second great discovery. He had made his first about ten hours before, but he didn’t know it yet.

  Around the lip of the crater, lying where they had been thrown up by the great explosions that had convulsed the lunar landscape three hundred million years before, were immense piles of rock which must have come from many miles down in the moon’s interior. Anything he could do with his little drill, thought Paynter, could hardly compare with this. Unfortunately, the mountain-sized geological specimens that lay all around him were not neatly arranged in their correct order; they had been scattered over the landscape, much farther than the eye could see, according to the arbitrary violence of the eruptions that had blasted them into space.

  Paynter climbed over these immense slag heaps, taking a swing at likely samples with his little hammer. Presently his colleagues heard him yell, and saw him come running back to them carrying what appeared to be a lump of rather poor quality glass. It was some time before he was sufficiently coherent to explain what all the fuss was about – and some time later still before the expedition remembered its real job and got back to work.

  Vandenburg watched the returning party as it headed back to the ship. The four men didn’t seem as tired as one would have expected, considering the fact that they had been on their feet for two days. Indeed, there was a certain jauntiness about their movements which even the space suits couldn’t wholly conceal. You could see that the expedition had been a success. In that case, Paynter would have two causes for congratulation. The priority message that had just come from Earth was very cryptic, but it was clear that Paynter’s work there – whatever it was – had finally reached a triumphant conclusion.

  Commander Vandenburg almost forgot the message when he saw what Paynter was holding in his hand. He knew what a raw diamond looked like, and this was the second largest that anyone had ever seen. Only the Cullinan, tipping the scales at 3,026 carats, beat it by a slender margin. ‘We ought to have expected it,’ he heard Paynter babble happily. ‘Diamonds are always found associated with volcanic vents. But somehow I never thought the analogy would hold here.’

  Vandenburg suddenly remembered the signal, and handed it over to Paynter. He read it quickly, and his jaw dropped. Never in his life, Vandenburg told me, had he seen a man so instantly deflated by a message of congratultion. The signal read: WE’VE DONE IT. TEST 541 WITH MODIFIED PRESSURE CONTAINER COMPLETE SUCCESS. NO PRACTICAL LIMIT TO SIZE. COSTS NEGLIGIBLE.

  ‘What’s the matter?’ said Vandenburg, when he saw the stricken look on Paynter’s face. ‘It doesn’t seem bad news to me, whatever it means.’

  Paynter gulped two or three times like a stranded fish, then stared helplessly at the great crystal that almost filled the palm of his hand. He tossed it into the air, and it floated back in that slow-motion way everything has under lunar gravity.

  Finally he found his voice.

  ‘My lab’s been working for years,’ he said, ‘trying to synthesise diamonds. Yesterday this thing was worth a million dollars. Today it’s worth a couple of hundred. I’m not sure I’ll bother to carry it back to Earth.’

  Well, he did carry it back; it seemed a pity not to. For about three months, Mrs P. had the finest diamond necklace in the world, worth every bit of a thousand dollars – mostly the cost of cutting and polishing. Then the Paynter Process went into commercial production, and a month later she got her divorce. The grounds were extreme mental cruelty; and I suppose you could say it was justified.

  Watch this Space

  It was quite a surprise to discover, when I looked it up, that the most famous experiment we carried out while we were on the moon had its beginnings way back in 1955. At that time, high-altitude rocket research had been going for only about ten years, mostly at White Sands, New Mexico. Nineteen fifty-five was the date of one of the most spectacular of those early experiments, one that involved the ejection of sodium onto the upper atmosphere.

  On Earth, even on the clearest night, the sky between the stars isn’t completely dark. There’s a very faint background glow, and part of it is caused by the fluorescence of sodium atoms a hundred miles up. Since it would take the sodium in a good many cubic miles of the upper atmosphere to fill a single matchbox, it seemed to the early investigators that they could make quite a fireworks display if they used a rocket to dump a few pounds of the stuff into the ionosphere.

  They were right. The sodium squirted out of a rocket above White Sands early in 1955 produced a great yellow glow in the sky which was visible, like a kind of artificial moonlight, for over an hour, before the atoms dispersed. This experiment wasn’t done for fun (though it was fun) but for a serious scientific purpose. Instruments trained on this glow were able to gather new knowledge about the upper air – knowledge that went into the stockpile of information without which space flight would never have been possible.

  When they got to the moon, the Americans decided th
at it would be a good idea to repeat the experiment there, on a much larger scale. A few hundred kilograms of sodium fired up from the surface would produce a display that would be visible from Earth, with a good pair of field glasses, as it fluoresced its way up through the lunar atmosphere.

  (Some people, by the way, still don’t realise that the moon has an atmosphere. It’s about a million times too thin to be breathable, but if you have the right instruments you can detect it. As a meteor shield, it’s first-rate, for though it may be tenuous it’s hundreds of miles deep.)

  Everyone had been talking about the experiment for days. The sodium bomb had arrived from Earth in the last supply rocket, and a very impressive piece of equipment it looked. Its operation was extremely simple; when ignited, an incendiary charge vaporised the sodium until a high pressure was built up, then a diaphragm burst and the stuff was squirted up into the sky through a specially shaped nozzle. It would be shot off soon after nightfall, and when the cloud of sodium rose out of the moon’s shadow into direct sunlight it would start to glow with tremendous brilliance.

  Nightfall, on the moon, is one of the most awe-inspiring sights in the whole of nature, made doubly so because as you watch the sun’s flaming disc creep so slowly below the mountains you know that it will be fourteen days before you see it again. But it does not bring darkness – at least, not on this side of the moon. There is always the Earth, hanging motionless in the sky, the one heavenly body that neither rises nor sets. The light pouring back from her clouds and seas floods the lunar landscape with a soft, blue-green radiance, so that it is often easier to find your way around at night than under the fierce glare of the sun.

  Even those who were not supposed to be on duty had come out to watch the experiment. The sodium bomb had been placed at the middle of the big triangle formed by the three ships, and stood upright with its nozzle pointing at the stars. Dr Anderson, the astronomer of the American team, was testing the firing circuits, but everyone else was at a respectful distance. The bomb looked perfectly capable of living up to its name, though it was really about as dangerous as a soda-water siphon.

  All the optical equipment of the three expeditions seemed to have been gathered together to record the performance. Telescopes, spectroscopes, motion-picuure cameras, and everything else one could think of were lined up ready for action. And this, I knew, was nothing compared with the battery that must be zeroed on us from Earth. Every amateur astronomer who could see the moon tonight would be standing by in his back garden, listening to the radio commentary that told him of the progress of the experiment. I glanced up at the gleaming planet that dominated the sky above me; the land areas seemed to be fairly free from cloud, so the folks at home should have a good view. That seemed only fair; after all, they were footing the bill.

  There were still fifteen minutes to go. Not for the first time, I wished there was a reliable way of smoking a cigarette inside a space suit without getting the helmet so badly fogged that you couldn’t see. Our scientists had solved so many much more difficult problems; it seemed a pity that they couldn’t do something about that one.

  To pass the time – for this was an experiment where I had nothing to do – I switched on my suit radio and listened to Dave Bolton, who was making a very good job of the commentary. Dave was our chief navigator, and a brilliant mathematician. He also had a glib tongue and a picturesque turn of speech, and sometimes his recordings had to be censored by the BBC. There was nothing they could do about this one, however, for it was going out live from the relay stations on Earth.

  Dave had finished a brief and lucid explanation of the purpose of the experiment, describing how the cloud of glowing sodium would enable us to analyse the lunar atmosphere as it rose through it at approximately a thousand miles an hour. ‘However,’ he went on tell the waiting millions on Earth, ‘let’s make one point clear. Even when the bomb has gone off, you won’t see a darn thing for ten minutes – and neither will we. The sodium cloud will be completely invisible while it’s rising up through the darkness of the moon’s shadow. Then, quite suddenly, it will flash into brilliance as it enters the sun’s rays, which are streaming past over our heads right now as we stare up into space. No one is quite sure how bright it will be, but it’s a pretty safe guess that you’ll be able to see it in any telescope bigger than a two-inch. So it should just be within the range of a good pair of binoculars.’

  He had to keep this sort of thing up for another ten minutes, and it was a marvel to me how he managed to do it. Then the great moment came, and Anderson closed the firing circuit. The bomb started to cook, building up pressure inside as the sodium volatilised. After thirty seconds, there was a sudden puff of smoke from the long, slender nozzle pointing up at the sky. And then we had to wait for another ten minutes while the invisible cloud rose to the stars. After all this build-up, I told myself, the result had better be good.

  The seconds and minutes ebbed away. Then a sudden yellow glow began to spread across the sky, like a vast and unwavering aurora that became brighter even as we watched. It was as if an artist was sprawling strokes across the stars with a flame-filled brush. And as I stared at those strokes, I suddenly realised that someone had brought off the greatest advertising coup in history. For the strokes formed letters, and the letters formed two words – the name of a certain soft drink too well known to need any further publicity from me.

  How had it been done? The first answer was obvious. Someone had placed a suitably cut stencil in the nozzle of the sodium bomb, so that the stream of escaping vapour had shaped itself to the words. Since there was nothing to distort it, the pattern had kept its shape during its invisible ascent to the stars. I had been skywriting on Earth, but this was something on a far larger scale. Whatever I thought of them, I couldn’t help admiring the ingenuity of the men who had perpetrated the scheme. The O’s and A’s had given them a bit of trouble, but the C’s and L’s were perfect.

  After the initial shock, I am glad to say that the scientific programme proceeded as planned. I wish I could remember how Dave Bolton rose to the occasion in his commentary; it must have been a strain even for his quick wits. By this time, of course, half the Earth could see what he was describing. The next morning, every newspaper on the planet carried that famous photo of the crescent moon with the luminous slogan painted across its darkened sector.

  The letters were visible, before they finally dispersed into space, for over an hour. By that time the words were almost a thousand miles long, and were beginning to get blurred. But they were still readable until they at last faded from sight in the ultimate vacuum between the planets.

  Then the real fireworks began. Commander Vandenburg was absolutely furious, and promptly started to grill all his men. However, it was soon clear that the saboteur – if you could call him that – had been back on Earth. The bomb had been prepared there and shipped ready for immediate use. It did not take long to find, and fire, the engineer who had carried out the substitution. He couldn’t have cared less, since his financial needs had been taken care of for a good many years to come.

  As for the experiment itself, it was completely successful from the scientific point of view; all the recording instruments worked perfectly as they analysed the light from the unexpectedly shaped cloud. But we never let the Americans live it down, and I am afraid poor Captain Vandenburg was the one who suffered most. Before he came to the moon he was a confirmed teetotaller, and much of his refreshment came from a certain wasp-waisted bottle. But now, as a matter of principle, he can only drink beer – and he hates the stuff.

  A Question of Residence

  I have already described the – shall we say – jockeying for position before take-off on the first flight to the moon. As it turned out, the American, Russian, and British ships landed just about simultaneously. No one has ever explained, however, why the British ship came back nearly two weeks after the others.

  Oh, I know the official story; I ought to, for I helped to concoct it. It is true as f
ar as it goes, but it scarcely goes far enough.

  On all counts, the joint expedition had been a triumphant success. There had been only one casualty, and in the manner of his death Vladimir Surov had made himself immortal. We had gathered knowledge that would keep the scientists of Earth busy for generations, and that would revolutionise almost all our ideas concerning the nature of the universe around us. Yes, our five months on the moon had been well spent, and we could go home to such welcomes as few heroes had ever had before.

  However, there was still a good deal of tidying up to be done. The instruments that had been scattered all over the lunar landscape were still busily recording, and much of the information they gathered could not be automatically radioed back to Earth. There was no point in all three of the expedition staying on the moon to the last minute; the personnel of one would be sufficient to finish the job. But who would volunteer to be caretaker while the others went back to gain the glory? It was a difficult problem, but one that would have to be solved very soon.

  As far as supplies were concerned, we had little to worry about. The automatic freight rockets could keep us provided with air, food, and water for as long as we wished to stay on the moon. We were all in good health, though a little tired. None of the anticipated psychological troubles had cropped up, perhaps because we had all been so busy on tasks of absorbing interest that we had had no time to worry about going crazy. But, of course, we all looked forward to getting back to Earth, and seeing our families again.