The Guardian du lieu suivant : London, Greater London, England • 6

SCMEXCE TO-M9A Venus, in blue light, 200-inch photograph, Mount Wilson and Palomar observatories SUN ftr our rwxj I Scientific orrestttrt den r- uvittJh there is no chance that a similar mechanism can be at work on Venus (which has no satellite and is too far from the earth). However, it ia possible that the ashen light mav be the resu.t of scattering of sunlight on the hign and largely transparent surface of Venus in much the same way as is now known that ultraviolet light from the sun can be scattered on to the dark side of the by hydrogen at heights above 1.000 kilometres in the earth's atmosphere. A further field of study which has not been energetically pursued is the study of the shapes of the sharp pointed cusps of the planet in its extreme crescent forms just before and just after inferior conjunction. That these cusps are brighter than the rest of the surface has been suggested for several decades, but, only recently has Dr James Edson in' the United States pointed out that a sufficiently careful study of these questions could help substantially with an understanding of the atmosphere. A series of photographs which he and his colleagues have obtained show that at new planet Venus often surrounded by a complete ring of light in which, moreover, irregular brightnesses can be discerned.

These phenomena must be due to the refraction of sunlight in the atmosphere of the planet and its transmission towards the earth. Tentative interpretations of these photographs have not yielded convincing results, but in principle it should be possible to infer from them a great deal about the extent of the atmosphere and the variation of its properties with height. Ironically in these days when dozens of scientists may be engaged for a year or more on the preparation of a single satellite experiment, Dr Edson complained in public less than a year ago that he could not find an astronomer who was prepared to devote himself to this more tedious task. As a result of the uncertainties of present knowledge and understanding of Venus it is not surprising that there are conflicting views of what it would be like to live there. On this question everything turns on the presence or absence of water on the planet.

And there seems to be no doubt that if the solid surface of Venus is above freezing-point, there can be no water there. For if there were, the carbon dioxide in the atmosphere would be rapidly converted into carbonate rocks. Alternatively it may be that the surface temperature of Venus is below the freezing-point of water, when it might be imagined to be covered with a layer of ice. In other words, the picture of the surface of Venus as a dry and extremely hot kind of greenhouse is starkly opposed to the notion that on its surface everything is frozen hard in a matrix of ice. For various reasons intermediate views are less tenable.

In the circumstances it cannot be expected that a rocket to orbit ofT Venus will do much to throw light on this question, though it will be especially interesting to see whether there are variations of the composition of interplanetary matter along the route. But in the end it is probable that the safest guide to an understanding of what Venus is like will be to go there and see. Rotation of Earth JSSl jpjpdp VTTHERE do we go from here This is what the astronauts have been asking themselves ever since the last Russian rocket brought back a picture of the moon. And by now there seems to be little doubt that Venus will be the next target for the rocket engineers. Indeed if rumours current for some weeks are correct, it is probable that the Americans aim a rocket towards the orbit of this planet within the next few dav.

Jt will be recalled that two rockets of this kind were meant to have hecn launched from Cape Canaveral lust June. The choice of Venus rather than of Mars for example as the next target in interplanetary balli.sti.-s is sensible enough. For a number of reasons it should he easier to send a rocket to this planet than to any other, and a i-ncul deal easier recover information from the flight, largely because tne planet comes closer to the earlh than any other a mere 2fi 0r 21 million miles at approach compared with between million miles and fi.D million mi'es for Wars. Then there are good reasons for wishing urgently to know more about the nature of Venus, for oven though it is the nearest of the planets it is in many respects the most puzziing. Even such simple facts as the time taken for the planet to revolve once on its axis wherever that may be are still unknown.

The composition of the planet's atmosphere is equallv a mvsterv the fact that large proportions of carbon dioxide have been identified there does not assist towards an easy understanding. However it is unlikely that the forthcoming rocket venture will succeed in yielding much information on these points or even in getting vcrv close to the planet. It will be nearly a vear fnn January in, 11)611 before the relative positions of the earth and Venus are suitable for a close encoun to account for the absence of permanent features on the observed disc of Venus. To be sure astronomers have for more than two centuries reported dark shadows on the visible surface, but others have shown how easily these could be simulated by optical illusions as much dependent on the telescopes used as on the nature of Venus. Probably this question will not be settled until it is possible to look at the planet from outside the atmosphere of the earth, but the unfortunate consequence is that it has not yet been possible to tell how quickly Venus may be rotating, or even whether it is rotating at all.

By following the motion of dark patches on the surface of the planet, and by accepting that they are real, estimates of the period of rotation ranging from fifteen hours upwards have been produced by more than a hundred different observers. The view that Venus does not rotate at all in the sense that it keeps one face permanently pointed towards the sun is supported by a large body oi influential but necessarily ill-informed opinion. The best that can bp said is that the shorter periods of revolution would seem to be contradicted by the absence of any detectable flattening of the planet, while the tidal influence of the sun might be expected in time nobody knows just how much time to bring about a permanent one-sidedness of the planet. Unfortunately no assistance on this point has been provided by a comparison of the measured temperatures of the dark and the sunlit side of lh planet, mainly because of the great variation in the results obtained. which range from minus 30 degrees to plus 60 degrees centigrade.

The chemical composition of the atmosphere has been studied with most of the methods now available to astronomers, but so far only one predominant conclusion has emerged that the atmosphere of Venun contains large proportions of carbon dioxide. This material can be recognised by its characteristic spectral lines. Attempts to discover the presence of water and of oxygen by the use of similar techniques have universally failed. Suggestions based on chemical speculation, current since the war, that the atmosphere of the planet might contain strange materials like formaldehyde have not been confirmed by observation, though in this field it is necessarily difficult to know how much weight should be given to a negative conclusion. Two other routes to an understanding of Venus which might be expected to yield some information about the structure of the planet have not so far met with much success.

There is, for example, the existence of the ashen light reported on several occasions to have been observed when the planet is near inferior conjunction and when the sunlit side of the planet is pointed away from the earth. Then, it is said, the dark side of the planet can be seen to glow faintly and much more faintly than the sunlit surface. This phenomenon is similar in appearance to the moonshine of the new moon in which a bright crescent is seen to embrace a faint image of the satellite itself. But moonshine is due to the reflection of sunlight from the earih to the moon (and back again) and Venus i Tt-elaf-ive I Ear? I Possible elliptical orbit of ro ckef crossing orbit of Venus urn tiwmm ter between a rocket and the planet. Urr.il then the best.that can be done will be 'o send a rocke.

towards" the orbit of the fi.iinet about the sun in the hope that this will yield information about that region of space which wi.l bear on a more complete understanding of the sun's influence there and only indirectly on the many problems of Venus itse'f. The mechanical problems of sending to the nearer planets have been extensively worked over bv several authors in (he last half-century, and there is hale doubt. that tnese earher calculations have now been substantially refined by means of electronic computers. The essentials of the situation do not however demand the use of these elaborate techniques. Venus moves about the sun in one of the most perfectly circular of a't p.anetarv orbits.

Its average distance from the sun is 67.2 million miles-some per cent of the corresponding distance for the earth. This distance fluctuates from one part of the Cytherean year (Cvtherean Venutian) to another bv no more than 4.5lt,r)0" miles, or bv 0.07 per cent. Because the planet's orbit is smaller Irian that of the earth, and because the gravitational attraction of the sun is therefore greater, the speed of Venus in its orbit must be greater than the speed of the earth. These figures are respectively 21.7 miles a second and 1R.3 miles a second. Similarly the gravitational situation implies that the length of the Cvthet-ean vear the time taken for one revolution about the sun should be less than a terrestrial vear.

The numerical value is 244.7 davs or 62 -per cent of the terrestrial vear. (The quantities concerned are the sidereal years, or the times taken to complete one revolution of the orbit against the background of the fixed stars It follows from this that any attempt to send a rocket to Venus or The Presidential Palace, Brasilia, the to Northern Ireland and the Continent neighbourhood must consist in making it move in an elliptical orbit aboir: the sun of such a form that the most elongated part of the orhit must extend to the distance of the earth whence the rocket must start from the sun. and that ellipse should at some point cross the orbit of Venus. This in turn implies that the rocket must escape from the gravitational influence of the earth with such a speed and in such a direction that it would seem to be moving about the sun with a somewhat less than that of iho earth in its orbit about the sun. For when this is accomplished the rocket's speed relative io the sun will not suffice to maintain a stable orbit at the earth's distance, and the object will be diawn in towards the sun on a curved path along which its speed will increase to and beyond the point at which a stable orbit would be possible.

This situation is indicated in the diagram, but for rocket engineers on the earth docs not appear in such a simple form. So that the rocket should become a satellite of the sun and not merely of the earth, it is of course necessary that its speed at launching should be greater than the seven miles a second or so needed to surmount the earth's gravitational field and thus to escape into space. But a rocket fired from the earth with a speed virtually identical to this escape velocity would only just escape from the earth's gravitational influence, so that after several days it would appear from the sun to be moving roughly in the earth's track with a speed only negligibly different from that of the earth. So that this speed should be sufficiently different and smaller than that of the earth in its orbit it is necessary that the velocity at launching should be substantially greater than seven miles a second and that the launch should be so timed that the rocket will appear from the earth to move backwards along the earth's orbit. This inci- new capital of Brazil.

Architecf.Oscar.Nicmeye PLASTICS, PAIST, WOOD PULP dentally implies that the launching of a rocket to Venus should take place towards dusk or, more accurately, that a rocket accurately bound on a feasible course to the planet should spend several days at the beginning of its journey in a position in the sky such that it would reach its zenith at dusk when observed from any point on the earth. The most economical means of launching rockets like these have been considered in some detail by people like Hohman (who produced his calculations before the first war). In this context the concept of economy is that of minimising the launching velocity needed to send a rocket to Venus. If full advantage is taken of the variations of speed and distance from the sun of the earth in its orbit. Hohman calculated that the most economical journey of a rocket to Venus would take 146 days, and that the launching should be timed to take place exactly 87.

6 days before the time at which the two planets were closest together and in a direct line with the sun the inferior conjunction as it is called. Such a rocket might be expected to come very close to Venus and would thereafter travel in an elliptical path taking 2Q2 days to encircle. Necessarily, occasions when these most efficient journeys may be started are comparatively rare inferior conjunctions recur at intervals of 440 days. Then because these ideal orbits entail comparatively small differences of speed between the rocket and the earth, the accuracy with which they can be guided to a close encounter with Venus is necessarily smaller than it would otherwise be. (Considerations like these presumably Influenced the Russians in their avoidance of the most economical orbit in the launching of Lunik II the rocket that landed on the moon.) Finally, there is the difficulty that such an ideal encounter with Venus would take place nearly 59 days after inferior con i unction, bv which time the distance between the two planets would have increased from its smallest value to something like 60 million miles.

This would entail that power of radio transmitters needed to send information back from the rocket during the close encounter would be nearly ten times as great as that needed in the most favourable circumstances, when the eartn and Venus were closest together. These arguments imply that actual attempts to guide rockets to Venus will be made at higher launching speeds than those known to be most economical, so that the time taken to travel to the planet will be substantially reduced from 146 days, and mat me rocnet so launched will travel in an ellintical the sun whose period of rotation is less than twice this amount. ine launching which is now imminent from Cape Canaveral will not, however, be able to arrange for a close encounter between a rocket and Venus when the planet is reasonably near the earth, for the planet is now still moving farther away from the earth towards the superior conjunction (on June 22 this year) when it will be on the opposite side of the sun from the earth. In these circumstances the venture will be valuable principally for the test it will provide of techniques for communicating by radio over vast distances. The record so far is close on half a million miles the point at which the batteries of the American Space rocket loot- failed.

If communication over tens of millions of miles is to be possible, substantial improvements of technique will have to be built into the new rocket. For one thing it is plain that the rocket will have to get most of its bower from the energy collected by Iwht Even so the total f'P' the power supply will Probably be close on 1001b It will further be necessary that radio transmission should only be carried an hour a day. and that the fullest use should be made cf modern techniques of using an extremely narrow range of Fadio fr carr'ine information back from a rocket. Informa- availab'e from the united States suimoctc these devices and with the help of sensitive radio receivers 9. radio-telescope at Jodrel! Bank-it should be possible from6f 1V badcast transmissions from a rocket bound for Venus over miles.

But obviously it will be a substantial technical triumph. if this in practice-and if the course of the rocket can be fol owed for a substantial part of its orbit about the sun is all this for? Why shou'd here be such interest in Venus Part of the reason is its expected similarity to the earth. Its masfor example. four-fifths of that of the of between 'nn "inn ye is on-v some1 son or 4no les than 'hat of similarity tne ner. of the two planets i )j.

iMair suppose that their i-umposiTion is similar so m.gnt be expected that Venu wpu.rf snow the same geophyica' features can be observed op the eartn. Th.s is a false expectation, i Mo. probably the dramatic I deferences wmch astronomers 1 ooserve are to be accounted for bv the greater intensity of unifh't must fall on the atmosphere of enus tnough the planet is -3 mil. ion miles nearer to the suit is the earth, solar radiation must be nearly twice as intense. But so far there is no clear understanding uj.

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