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The National Association of educational broadcasters with the cooperation of the California Academy of Sciences and radio station KPFA in Berkeley presents a program in the recorded series astronomy for the layman on today's program. Leoni Sellon a lecturer in astronomy at the Morrison Planetarium of the academy and John Hopkins an inquisitive layman discuss the origin of the solar system. Mr. Hopkins begins the discussion Leon knowing that you spend much of your time describing and demonstrating the features of our galaxy to the public at the Martian planetarium in San Francisco. You must be the target of all sorts of astronomical questions. For many of these YOU course have exact answers. But what can be done with a fundamental and I suppose a basically unanswerable question Mike. What's the origin of the sun. The origin of the earth origins of the other planets satellites. Well John you put your finger on it right there when you said basically unanswerable
at least for the time being the question has no definite answer and is in fact considered the most difficult question of contemporary natural science questions of origins generally are hard to get at. But in the question applied to the solar system they have an extraordinary difficult thing. But we have an assemblage of planets going around a star that star being our sun. There are nine of these planets attended by 31 moons all together are so-called satellites. In addition to these there are over fifteen hundred cataloged asteroids and unknown numbers of comets and needy orcas. Well Molly when you speak of it this way this sounds like a sort of just an assemblage of parts is there any order to be brought out of this. Yes the order which is exhibited by the solar system is one of the basic things which has to be explained for we have in the case of the
planets the nine principal planets that is paths which are approximately circular that Jackley ellipses to be precise. These are spaced in a fairly regular way from the central Sun the directions of motion are uniform. The directions in which the planets spin will rotate agree approximately with the direction in which they revolve as do the directions of the motions of their satellites. There are exceptions to these things but the tendency is as I've just outlined and these are all regularities and it can be shown that the chances are extremely small that this all could have come about. Fortuitously. I don't know of an exact comparison that one might think of it this way. If you were to put 10 children to play it ten typewriters and then assemble the papers that they had written on and then put this all together and expect to have a sensibly written book in order. You might as well expect that the solar system came together just
by chance. That certainly indicates that there are lines of thought upon which one can approach an answer although perhaps not have a final answer to this question. Yes as a matter of evolution and given certain conditions at beginning how did the thing come about to its present state. That is the question of what should be destroyed and I would like to be able to answer some degree of certainty. Of course I realize that the Greeks and I guess the Egyptians perhaps even other peoples before them made attempts at this. But I don't know how close they came. Oh yes they were always cosmologies the one most familiar to us in our present time and civilizations perhaps the account in the bible of Genesis. But it was seen rather early some centuries ago to be exact that this was inadequate for these accounts. Suppose that the whole thing came about in a rather sudden fashion.
Rather you might say they were it was one of the single act of some supernatural being. And the time that was thought of in those instances was shown to be quite insufficient for a study of this by the geologist progress. It was evident that we were not dealing with matters of days in describing the evolution of the sun's family. But it was rather a matter of hundreds of millions if not billions of years. And so we are of course concerned not with scientific explanations which make use of vast Lanse of time and enormously extensive processes of involving matter and motion. Was that the first change in our line of thinking. The time element is that of the people who began thinking about this after the days of the Greeks and the Egyptians. It was at the time element that first got them started on a new track.
I think that's correct because the traditional account said made it seem as though the event of events could have taken place in the rather short time conceivable to the finite mind of man. While the geological evidence piling up gradually showed that indeed these events must have taken enormous to long times to be completed. That's a rather indefinite long time is it really really how long do you mean. Well one can say several billion years perhaps. In the case of the past history of the sun the solar system. I'm speaking only of their origins but of the evolution of the state in which we find them today. To whom do we owe our first debt. In this expanding the time scale I don't recall anyone in particular in the field of geology but as far as the astronomical interpretation is concerned I think we can start with the French one plus in the year 1796 he proposed a
theory on the system of the world in which he proposed that the planets around the sun condensed from a nebula which existed around the sun itself. Now of course you see we are faced perpetually with this problem of where the nebula come from. But let's make that quite clear before we go any further in these discussions. The scientists must be content with the following situation given certain beginning conditions. Can you be carried forward to a situation that resembles the state of things we find at present. If we can do that in one instance then can we push it back a little farther and gradually achieve progress in getting to an earlier or earlier stage of things. And so for the moment we will say that given certain initial conditions around the sun then how did the planets come to be. These plants are extraordinary interesting interesting things in themselves. And one of the
difficulties of any theory of the solar system is to account for the differences along with the similarities we have for example the inner planets Mercury Venus Earth and Mars which are comparatively small comparatively dense while on the other hand starting with Jupiter and moving on to Saturn with a measuring planet than Uranus Neptune. We have a rather large bodies Jupiter over 10 times the diameter of the earth. And these are also comparatively less dense. We have tacked on at the end rather than as an afterthought the most remote planet Pluto at a distance of four billion times four billion miles or forty times the distance from the earth to the sun now and it resembles not its neighbor and up to him but is more similar as age of the Earth or Mars. Well you see as these things have a variety in structure which would be explained it must be explained along with the whole assemblage.
When I did the theory as you know instead well a plus. Did it take care of all or most of these this wide variety of facts. When the state of astronomical knowledge as of 1796 the physical details of the plans were not known of course as a matter of fact your anus and only recently been. Found by Hershel the asteroids Neptune and Pluto were unknown and the details of the planets which were unknown were quite vague and incomplete as so we wouldn't expect an account of all these refinements. However lost is theory for supposing that the nebula around the sun which was spinning condensed and formed into rings which later gathered into the successive planets would explain a number of important details if indeed the theory was true in the first place. The details such as the fact the planets all go around the same
direction generally in nearly circular orbits orbits which are approximately in the same plane of space. And these things would follow naturally shall we say from an assumption of a nebula around a rotating star. Well these facts then I presume are the ones which were uncovered by Kepler. Those people I mean from them you knew the little plants knew that the plants did have these particular characteristics. Oh yes the general layout of the planetary orbits was fairly well known from the work of the men you mentioned. Also there was a curious relationship which astronomer boded had in seated shortly before which made it seem that the spacing of the planetary orbits followed a numerical pattern a sort of formula which should calculate in advance the spacing of the planetary distances. Well this simply fell into the pattern that the whole thing must of come about as a result of some regular natural forces.
So as far as it went they looked lost and theory was all right and was accepted as the best that could be contrived for almost a hundred years. Well but it was doomed to failure in a thawing way. A very important quantity in studying the motions of the planets is that known as angular momentum. Just just a minute Leon before you go ahead with angular momentum what is an angular momentum or angular momentum is a sort of measure of energy in a rotation. We have a certain mass of matter moving around a central point at a certain distance with a certain velocity. Well this isn't the ring of which you spoke in the elementary formula plus theory. Well the totality of it all really in that I think it would have gain your momentum because it would have mass. It would have distance from the center in this case the sun and it would have an ever last day of motion around.
But of course if it's a flat disk it if I thought you can't say it itself is located at any specific distance although maybe the major part of its mass isn't actually in the last unit area the material is supposed to have been distributed in a succession of rings and that rather pins down me. The average distance at least which this material is located. I suppose each ring then could be treated separately. Yes I am and the upshot of it is that this angle meant momentum quantity is calculated by combining my old cation the mass the distance from center and the velocity of the motion. Now when one calculates. The amount of angular momentum that is contained in the planet that is just the sum of of all the planets and computer angular momenta. And imagine at that one time I was in a nebula around the sun which was supposed to have flattened out and separated out condensed into planets. You would find that the amount of rotation or speed of rotation added to the sun in that process
would not be sufficient to make the sun spin fast enough to break up in the first place. For you see this angular momentum cannot be just created. It can only be transported from one part of a system say a rotating nebula to another. So whatever angular momentum on the simple theory is now in the planets a must at one time have been in the nebula which was peeled off one might say from the sun. No the words are there's no friction the last of the planets moving about the sun. That we can assume that whatever there is now is what there was to start with. Yes unless there's been some interchange with objects on the outside like a passing star. Well this all adds up to the simple conclusion that a rotating nebula around a star would not separate out and during which would condense in the planets in the first place we would simply remain as a gaseous matter around that star sun. So
the simple idea so beautifully and unseated by luck losses simply cannot provide the explanation for the existence of planets. Well the planets exist that's an obvious fact and so we have to pursue further an explanation of it. The turn of the century twentieth century found a considerable amount of activity in these investigations. Chamberlain more than a geologist and an astronomer respectively in jeans and Jeffrey's Any same combination worked up theories in which. It was thought that by the interaction of the star material was drawn out from the sun for by all people who generally agreed that the sun preexisted system of plants. Well this then is a theory based on a close approach or a passage of one star by another one of being our sun correct.
The idea being that if a star good comes near enough to the sun exert gravitational pull or tidal action it would dry out material and this material would be the stuff out of which planets could be formed. First of all we must realize that this could not be a very common event for the distances between the stars are very very great compared to the sizes of the stars themselves. I take our sun which is typical as a diameter of over a hundred thousand miles. But it is separated from its nearest neighbor in space the star Alpha Centauri at the present time by a distance of twenty six million million miles. This is considerably more space than separates the individual book shots in a widely scattered charge so the chances of collision are extremely remote. Someway one said that on the theories of Chamberlain molten jeans and Jeffries as a solar system had a narrow escape from happening at all.
Well go ahead I was going to as you said that it did happen though and it is here. Yes. Is there still is there theory still the theory to which we had here to moment no. You know it was demolished several Look up about a decade ago it was demolished by a physicist who calculated that the material which would be drawn out from the sun on such an account would be so exceedingly hot that a mass of it consisting of enough material to make a planet would not have sufficient gravitational pull to hold itself together and would simply parade or blow up in space. By this then you infer that it would be at such a temperature that it would be gaseous. Absolutely very low density. Absolutely the surface of the sun of the present time is at a temperature of about 11000 degrees Fahrenheit and a little bit below the surface must be up around a million degrees going to 20 million degrees at the center. And all present theories of the
evolutions of the stars indicate that the sun was not appreciably different. Take two billion years ago or three billion years ago when the planets were formed of the now. So we can appeal to any conditions very different from those we now find upon the sun. So basically this is the fatal difficulty the probability that the thing couldn't happen that tall is not a fatal one however. We don't like it because we've learned over and over again in astronomy and other natural sciences that we cannot put ourselves in a favorite position. So the chances are that solar systems that is systems of planets around stars are fairly frequent and we happened to be on one of a large number the old bugaboo angular momentum also enters into the difficulties of the so-called Title encounter theory that we've been talking about for it to be demonstrated that if a star came close enough to pull material out and therefore give it enough energy to go out from the sun
it couldn't get it out as far say as a planet and then just drop it off with sufficient and your momentum. The way we have it now and the way the system the present exists with a son with a 99 percent of all mass in the solar system has only 2 percent of the angle of angular momentum and so we have to explain either how the planets got so much anger or momentum or why the sun has too little if a successful theory could do that. And at the present point we haven't found a theory which will give it give us and that it would explanation of these difficulties may sound a little technical. Well but of course it's unavoidable for we are dealing basically with a very complicated thing and we can only hope to sketch in the very briefest outlines. The trend of our thinking along these lines in the matter. I remember reading in Harper's a discussion of some
parts of this by Mr Hoyle Fred Hoyle in which he he felt that our son must originally have been part of a double star. Has that theory received any particular credence. No it hasn't. The idea there was to eliminate the difficulty that the passing of a one star by a single star could not draw material out of the distance of Neptune or Pluto and doubtless sufficient angular momentum of the double star hypothesis being simply that what was encountered was a one of the components of the double star which was demolished by collision with the interloper from outer space and the fragments were drawn about in orbital paths which we now find. As the planets. This is no better from the point of view of the theory of the hot gas state where you see the star which was hit. It will be hot.
Stars are hot and this material would evaporate into your stellar space just as a title filament drawn from the sun. I think it's been said correctly that the Hoyle theory. Oh a little little theory might be an excellent way to produce a gigantic explosion but hardly to produce a closely organized and very delicate system such as that may have planets in thinking of the origins of the planets. It would seem as if of course that the source from which the planets came must have the same composition as the planets now do do we know enough even much say about the composition of the earth to know what should have been the composition of the parent body. Some of the most interesting speculations in cosmology take that point of view that you just brought out one of the best and most recent was not written by a doctor your evening of Chicago and his excellent book The Planets. He
takes the point of view that with our knowledge now of the chemical composition of the earth if Europe's crust least that of meteorites and of the atmosphere of the sun obtained by spectroscopic analysis we should be able with our knowledge of chemistry to predict rather accurately the original state of these things which of course is a step backward in time. Presumably getting a little closer to the question how did it all start. There are certain things which are clear. For example hydrogen is by far the most abundant element in the sun by weight. Helium second only Earth oxygen is the most abundant silicon and nitrogen are also very prominent. We would have to explain of course right off why there is so little hydrogen on the earth. We know however in going a little further in our investigations that large planets such as the huge Jupiter and the nearly as huge Saturn are composed
of ices and frozen materials on their surface which probably contain a great deal of hydrogen for it was in the water methane and ammonia principally. Well this would this gives a key you see it would appear then that a fast moving hydrogen atoms the lightest of all I could easily escape in the primordial state from the interaction of the earths whereas the larger planet would hold. So this seems to be a explanation at least of the discrepancy between the chemical composition of the sun and that of the earth. There are no insuperable difficulties here however. It isn't easy for it is for instance exceedingly difficult to know precisely the chemical composition of the Earth's interior. All we have to go by is the fact that there's a very high density comparable with that of iron nickel meteorites. So your best guess is that the center of the earth if solidified would be similar to the stuff we call an iron nickel meteorite. It's
reasonable on the supposition that in looking at these meteorites we are looking at things which are the remains of say a planet which was shattered during some long past time. But you have certainly put your finger on a very important consideration. And through all the subsequent theories of cosmology we will have to take very careful account of the agreement or disagreement of the chemical compositions of the objects we're talking about. Have you any other clues other than something like that as to where we must look for the parent body or parent material of which the planets are composed. Well we have learned in the last couple of decades that along with the stars and space there is a great deal of interstellar material so-called. It's composite a mixture of dust and gas gas of course as in the atomic and molecular state combinations of atoms while the dust
consists of very small particles of material which many thought of as fragments of a larger object and you can call them grains if you wish. Anything like that will do some of the stuff probably is as large as a grain of sand but most of the dolphins are very much more tiny such as the soot. Well this stuff is in abundance around among the stars. It is thought now that the origin of planetary systems must be sought in the conglomeration of dust clouds which may be near stars. We will find in later discussions that this is also important considering the origin of the stars themselves. But we are now just considering the formation of planets. And it turns out that the most recent theories have turned back to le plus an idea of a sun or some resemblance to what we know as the sun or rotating in the midst of a dust gas cloud. You like very well I
ask Well isn't that to progress backward Didn't we just leave the nebular hypothesis. Well it's a step backward with a difference. We go back to the original idea in form but we change greatly in detail. What we have learned quite a lot about the movements of gases and dust clouds around in rotation. These theories are in the subject called tribunes very important say in the study of motion of airplanes and rockets projectiles through the air. Such a thing goes through air it sets up Eddy is or circulation about violent circulation shock waves and the motions of these things can be observed and to a certain extent calculated. I think we can get credit largely to a brilliant German physicist astronomer Garland by seeker who in 1044 published the first edition of a whole series of subsequent theories which follow the same pattern. I've often thought rather wonderful that
a German astronomer in Germany in 1044 had time to think about the origin of the solar system when his own country was coming down about his ears. Be that as it may it's the truth. Well of course no doubt he didn't do it just during the war he probably had started thinking about it a long time before that. Oh of course. Well the substance of these modern theories is simply this. We do go back to the idea that the sun was in the midst of a rotating dust gas cloud that rings or zones of material were formed by the transmitted rotation. But now we introduce a new factor. The idea of the turbulence and the viscosity that is the resistance of materials like this to to flow. Everyone's seen whirlpools the little black currents that are produced the collection of the flotsam and jetsam in these little places. Well exactly in the same way it is thought that the interstellar material of the
dust and gas cloud. I formed pockets in pockets as these were said into rotation and into revolution. That is rotation spinning a revolution orbit about the sun. These orbits would have the general characteristics of those we observe. One of course wonders what happens to the angular momentum question. It's been pretty well demonstrated that the anomaly which would go on there would greatly reduce the amount of rotation in the sun and thereby explain the small thing or momentum of the sun and allowing the orbital motion the plans to have their seemingly disproportionate share of these things are not entirely clear at the present time. There is still much work being done but I think it's safe to say that we're on the right track and progress is being made. You've been listening to a discussion between Les on a cell in a lecture in astronomy at the Morrison Planetarium in San Francisco and John Hopkins an inquisitive layman
on the origin of the solar system the Ceres astronomy for the layman was recorded at radio station KPFA in Berkeley with the cooperation of the California Academy of Sciences. This is the end of the network.
Astronomy for the layman
In the beginning
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pacifica radio
KPFA (Radio station : Berkeley, Calif.)
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University of Maryland (College Park, Maryland)
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Episode Description
This program discusses the origin of the Solar System.
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Six programs on astronomy featuring Leon E. Salanave, lecturer in astronomy at Morrison Planetarium in San Francisco, and John Hopkins, interviewer. Produced with cooperation of California Academy of Sciences.
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Interviewee: Salanave, Leon E., 1917-
Interviewer: Hopkins, John
Producing Organization: pacifica radio
Producing Organization: KPFA (Radio station : Berkeley, Calif.)
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University of Maryland
Identifier: 55-20-1 (National Association of Educational Broadcasters)
Format: 1/4 inch audio tape
Duration: 00:29:51
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Chicago: “Astronomy for the layman; In the beginning,” 1955-05-22, University of Maryland, American Archive of Public Broadcasting (GBH and the Library of Congress), Boston, MA and Washington, DC, accessed March 1, 2024,
MLA: “Astronomy for the layman; In the beginning.” 1955-05-22. University of Maryland, American Archive of Public Broadcasting (GBH and the Library of Congress), Boston, MA and Washington, DC. Web. March 1, 2024. <>.
APA: Astronomy for the layman; In the beginning. Boston, MA: University of Maryland, American Archive of Public Broadcasting (GBH and the Library of Congress), Boston, MA and Washington, DC. Retrieved from