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F* fr il 1i 1i INTROD(TCTION AND GENERAL STATEþIENT THE NATURE OF ASTRONOMY Astronomy has as its domain the study of the celestial bodies-the sun, planets, stars, clouds of gas between tìre stars, galaúes-and indeed the entfue universe considered as a single system. A.stronomy's goal is to leam the nature of these diverse obiects and to relate their properties, their motions, and their distribution in space in a uniffed world picture; to under- stand the evolutionary development of the universe from the time of íts formation to the present epoch of obsérvation and beyond; and indeed, to discover, if possible, its original st¿te and its ûnal destiny. Unlike other sciences, where subtle and detailed experimentation can be done ulder controlled conditions in the laboratory, astronomy must be content to study the experiments tflat nature herself makes, 'þerformed' in space by natural causes under uncontrolleil conditions. Àll knowledge rnust be gleaned from the radiation coming from the obiects under study. Although this transfer link is a feeble one, the light beams carry ân amazing of ioformation. Interpretation of the data using the laws of physics "-orrrrianow them ( d}'namics, atomic and nuclear physics, thermodynamics, as we l plasma physics) has proiluced our present untlerstanding of the external universe. DEVELOPMENT OF A WORLD PICTURE Astronomy is the oldest of the sciences. As soon as man could write, he preserûed his thoughts antl speculations about the universe around him on cuneiform clay tablets, on papyrus, and in the Greek anil Arabic documents that form our ieritage. Ancient man observed the daiþ rising and setting of the sun, its annual ioumey northward anil southward which produced the Copyright © National Academy of Sciences. All rights reserved.

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of the moon, and the wandering of the planets against seasons, the phases the background of the "ffxed' stars. These regularities of tle cosmos câr¡sed much wonder, and out of speculation arose tlose systems of cosmology with which the history of astuonomy is written. In the earþ days of civilization, astronomy had a major role in forming man's concepts of his place in space and time. Primarily as a result of discoveries by Aristarchus, by Ptolemy, by Copemicus, Galileo, Tycho, Kepler, and Newton, man's view of nature passed through a long series of profound revolutions. Earþ man naturally considered the earth to be the center of the u¡iverse-the ffxed stars, tl-re planets, and the sul being creations of the gods or even gods themselves. When regularities within tle system wele discovereil, the geocentric theory with its crystalline spheres and epicycles was invented to explain tìre mo- tions. This theory culminated in the Ptolemaic geocentric tables of planetary conffgurations. Unexplained discrepancies led certain visionaries to con- sider the sun rattrer than the earth to be the center of the world, but tlis hypothesis was so foreign to the ancient mind that not until the middle of the 16th century did Copernicus force a recognition of a heliocentric uni- verse. The transition was so painful that Giordano Bruno lost his life for teaching it and Galileo was forced to recant his belief before tbe Church in Rome. But r¡¡ith the discoveries of the laws of planetâry motion by Kepler and Newton, the revolution was complete. In modem times, an equally profound hansition has occurred with the recognition that the sun, with its planets, is one of a million million other stars comprising a large, flattened, slowly rotating system called the Miþ Way galaxy. In tum, our galaxy, as a membei' of a local cluster of nearby galaxies, is but one of billions of other galaxies that make up the universe. And, in a discovery of deepest signiÊcance, the entire system has been found to be in a state of rapid expansion, each galaxy receding from every other. Less than 50 years have passed since tlis worlcl picture, with tÌìe atoms ordered into stars, stars into galaxies, galaxies ínto clusters, and clusters embeclded in expanding spacè, was established with certainÇ from observa- tions with the large telescopes constructed within this century. No armchair speculation could have coniured tç such a hierarchy of systems to bring order out of apparent chaos. Yet nature, in some way yet dimly appreciated, has fashioned herself into such a pattem. Can we hope to lèarn how or when? Can we comprehend this structu¡e as a sequence of events, each ¡¡nderstandable in itself, un{olding in time? In the broailest sense ttris is the purpose of research in astronomy. Detailed projects on a multitude of sub- 2 Copyright © National Academy of Sciences. All rights reserved.

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w""' ffi xl iects are leading, each in its own wa¡ toward tlis goal. .t¡ il Knowledge tlrat seemed impossible to obtain 50 years ago is now either rì routineþ lnown or c¿n be found with our present capabilities. Today some ,11] of the cleepest problems of ashonomy and cosmology appeat to be on the ,.i verge of fielding. We know the distances to stars, their sizes, surface temperatures, and the abundances of the ehemical elements that comprise tÏ.eir surface layers. We Ïnow their space motions witlin the galary, their ages, tìeir evolutionary history, and tleir probable fate. But tlere are many tTings we don't know. How are stars formed? Why do they condense from tåe interstellar medium into double, triple, ancl multiple systems that revolve around each other in gravitationaþ stable conffgurations? Why do some possess suong magnetic ffelds wble others do not? How ilid the gahxiãs come into ;xistence? \Mhat is the origin of ratlio signals from stars ánd galaxies? What is the origin of cosmic rays, and what are tÌre nuclear processes that give rise to the high-energy gamma rays and X-rays that ipace probes are iust beginning to observe? Perhaps the most {undamental question of all concems the origin of the large-scale ordered magnetic ûelds that recent studies in radio astronomy have found to exist in certain regions of space. Ànswers to some of these questions will undoubtedly come within the next decade; others, now only dimly perceiveil through the mists of present ignorance, must wait until ou¡ present larowledge can be broadened. Progress will be made by clever and aggressive use of telescopes of the largest size, equipped with detectors such as radio receivers, spectrographs, photometers, and photographic plates-instrùments that anaþze the faint incomíng radiation maile feeble by the enormorrs spreading out that has taken place in its long jourrrey ftom its place of origin to the earth. ROLE OF THE UNTTED STATES IN ASTRONOMTCAL RESEARCH r Optácal Astrorømg t, Since 1900, the United States has held a dominant position in much of I observational astronomy. The discoveríes ftom which the present world h picture has emergeil have aünost invariably come from observatories in ttris e ãountry. This was no accident; it came about between 1900 and 1950, ¡Á,j.,. Copyright © National Academy of Sciences. All rights reserved.

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solely because a few aggressive, inspired, and imaginative men in this cor:¡- try secured private fùnds to design and build the large telescopes with which tåe present frontièr position in astrophysics was reached. WitÏout these instruments, buiìt in a period when government supþort did not exist, the lmowledge we have today would have been denied us, The ffrst sys- tematic study of tÏe distances to nealby stars could begin in Ameriea in the earþ 1900t with the long-focalJength refractors at the ,A,llegheny Observa- tory ( Pittsburgh), at the Yerkes Observatory (Chicago), at the Sproul Ob- servatory (Swarthmore), at the Van Vleck Obse¡vatory ( Connecticut Wesleyan ), and several otfrers-because these large telescopes existerl. The discovery of ttre form of our galaxy in 1915 as a higtrly flàtened rotating disk of stars, with the sun and its attendant planets at a peripheral position 30,000 light years from its center, would not have been possible without the 60-inch reflector on Mount Wilson. The discovery of the tme nature of the extemal galaxies as separate island universes" was possible in Ig24 because the 36-inch Crossley reflector of the Lick Observatory ancl the 60-inch and 100-inch telescopes of Mount Wilson were available. And the expansion of the u¡riverse could be fou¡d in 1929 and studied adequateþ from 1g2g to 1938 only with tÏe 100-inch and 36-inch Crossley reflectors and their efieciive nebular spectrographs. Without this progression of instruments .iii of increasing size, equipped with detectors of high sensitivity and sophís- rd tication, asûophysics would yet be largely in an infant state. JT rI Radin Astronomg it ,tl In the new science of radio astronomv, it was the pioneer discoveries of jil young American scientists in the 1930's that opened up t]1e ûeld. The 1.å ìÌ fundamental iliscovery came in 1931, when Karl G. Jansþ of the Bell rã Telephone Laboratories found that radio waves were arriving from space at iÌ an intensity level a million million times greater than could be explained r by the known properties of astronomical bodies. In the late IgS0 s thà raclio ,l amateur Grote Reber surveyed the heavens with a S2-foot paraboloid t{ iì erected in his back yard in Wheaton, Illinois, and produced the frst coarse I map of the radio sþ. These promising beginnings were followed up, how- ever, by bold developments in other countries, and tÏe U. S. position over i tÏe past 15 years of rapid growth has not been dominant. l.! In the postwar years, it was the highly talented European and Aus- ìi tralian scientists, rather than the Americans, who advanced radio astronomy l by adapting wartime electronic developments to the observation of radio- 4 Copyright © National Academy of Sciences. All rights reserved.

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frequency radiation lrom extraterrestuial obiects. Discrete radio sor¡¡ces t- *".L ,oon discovereil, and a treasure trove \¡/as openecl up. Large radio h telescopes. and antenna alrays we¡e bgilt in,{ustralia, Englancl, and the e Nettrerlands, and the United States fell far behincl. t, Serious U, S. efiorts in radio astronomy began in the earþ I950s witl ;- modest projects at the Naval Research Laboratory, where the trst 5O-foot e paraboloid was built, and at Comell University. À maior discovery came ir, 1g5t *h"o the Zl-centimeter railiation of hydrogen was detecteil by t- H. I. Ewen and E. M. Purcell at Harvard. Otlrer important U' S' cont¡ibu- rt tions incluiled tÏe discovery of powerful sporadic railio emissions ftom e ¡adio receiver' Jupiter antl the development of the low-noise maser-type project at Harvard, started in 1953, produced the ,4. radio astronomy n ûrst Ph.D.'s in radio aitronomy. Since 1955, tlevelopments at several uni- e versities, aided by enlightened federal support, have done much to regain e the ground lost whíle ãther countries were surging ¿}eacl. The National Radiã Astronomy Observatory, planned in 1954, is fulfflling its objective of J provrding radio astronomers from any part of the country witÏ instnments f L"yood [h. capability of a single university; its 300-foot transit-mounted 3 paiaboloid coniiderably extends the capabilities of 60- to 9O-foot parabo' r ioids available at several universities' Very recentþ, the completion of a s 1,000-foot, limited-coverage, ffxed-mirror radio telescope at Arecibo, Puerto Rico ( operated by Cornell University ), has given the United States a pre- eminent position in radio astronomy with single-mirror antenna systems' Theïnited States now plays an importânt role in nearþ aII aspects of radio ashonom¡ and in a few ûelds, such as planetary physics, it is in a dominant position. In the use of extended antennâ ârays to achieve high angula.r rJsolution, however, the United States is ileûcient World-wide coåpetition in radio astronomy is intense, and if the Uniteil- States is to keep pacJ with plogress elsewhere, and to realize the lruits of a revolutionary ã"u"lop-"it tÉat began on its own soil, the country must mount a iliversi- ffed and far-reaching program. CURRENT PROBLEMS of astronomical research of A brief survey of recent progless in aspects great current inte¡est deãonstrates the important role playeil by large instmments: Copyright © National Academy of Sciences. All rights reserved.

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Creation of the Chemì.cal Elam¿nts An important deveþment in astronomy during the 1950s has been the spectrographic discovery that the abundance of healy chemical elements in stellar atnospheres varies from star to star and is related to stellâr age. This fact strongly suggests that the elements are continuously manufac- tuled ín tÏe stars tìemselves under conditions of high temperature and pressure, and are clistributed by stellar explosions tluoughout the interstellar meùíum in which ne\ry stars are forme¿l. Here we have the shongest link between ttre large-scale world of ashonomy and the subatomic world of nuclear physics, because we see that the origín of atomic nuclei is tied directly to the astronomical events in outer space. The data would not have been obtained without the use of large telescopes equipped wíth mode¡n spectrographs. Neu Krøuled,ge from Ra.dìb Astronomg Some of úre great advances of the last 15 years have come through the application of radio astronomy methods. In this brief period, new and previously unsuspected phenomena have been foirnd by radio techniques, phenomena that are now changing old concepts and enlarging our víew of others. No portion of the observable universe has been left untouched by the efiects of radio observations; our knowledge concerning the sun, the moon, the planetary system, our galaxy, and distant galaxies has been vastly increased. In particular, the methods of radio astronomy have brought us a diversity of new knowledge-an improve¿l distânce to the sun, the conlgura- tion of the magnetic ûeld of Jupiter, tle temperature and structure of the invisible surface of Venus, the composition and roughness of the lunar su¡- face, the temperature of the solar corona, ttre density clistribution of neutral hydrogen in our galary, and a more complete picture of the rotation of our galaxy. Railio astronomy studies today play key roles in all aspects of the study of space, and continued rapid growth of their role in astronomical research appears certain. Erpbding Galnsi¿s Perhaps the most important radio astronomy discovery was that ce¡tain rare antl unusual galaxies emit prodigious quantities of radio energy by 6 Copyright © National Academy of Sciences. All rights reserved.

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some natural process not completeþ understood. We now have indications that these phenomena, whatever they may be, are connected with enormous e explosions occurring near tÏe centers of tlese systems-explosions that release t energy exceeding even that to be expected from nuclear transformations. Once beforg astronomers faced a símilar prot¡lem: what is the source of the energy of the stars? We need only recall tÏe tremendous consequences of l the study of that problem, which led to tÏe discovery and understanding of I thermonuclear energy souces, to appreciate the import of this greater k f pltzzf,e. The discovery of radio explosions in galaxies ís one of the most far- l reaching of our time because it shows, in addition to the existence of tìese catastuophic events, that general magnetic ûelds exist in space between the n stars ( and perhaps between the galaxies ), and thât large numbers of high- energy particles of udrnown origin are moving through tìese ffelds. The discovery undoubtedly provides the long-sought connection between astron- omy and cosmic rays. The process that produces the radio emission is called magnetíc bremsstrahlung or s¡,nchrotron radiation. It occurs when t high-energy electrons, traveling near the speed of light, encounter a mag- netic Êeld. They are deflected by the ûeld in a well-understooil way, and in ;, so doing are accelerated, wíth a subsequent emission of electromagnetic t radiation. For certaín ranges of electron energies ancl magnetic-ffeld shengths, this radiation is in the radio region of the spectrum. If the energies and ffeld strengths are high enough, part of the energy can also be radiated v in optical wavelengths, and there are well-known examples in which this occurs. The Crab Nebula, which is a lemnant of an ancíent supernova, is one such example, anil the exploding galaxy M82, shom in Figure 1, ís another. Direct evidence is available in M82 from optical polarization data to show that magnetic ûelds exist extending 10,000 light years from tlhe I center of the galaxy, and that high-energy electrons interacting with these r ffelds procluce the observed ¡ailiation. The implication of these data for cosmic-ray ashonomy and for the problem of the evolution of galaxies is enormous. v To learn more about these events in space we must have many types of h observational data. Information on the amount of radiation in difierent frequency ranges, i.e., the characteristic continuum spectrum of the sources, must be found. If we know the polarization of the radiation, we can map tle pattem of tÏe magnetic ffelds. The variation of the emitted flux with time gives i¡formation on the changing pattern of the telds or on the vary- ing energy clistribution of the electrons as the explosion evolves. Parallel Copyright © National Academy of Sciences. All rights reserved.

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witl large and intermediate-size optical telescopes, to studies are neeiled obtain: (1) optical identiffcation of the sources, (2) observations of tleir optical spectrum to ûnd ttre radial velocities in the expanding ulive¡se and hence their distances, and (3 ) their apparent luminosities so tìat the energies involved can be determined. Quasí-Stellar Radio Sour ces Within tle past year, the early stages of such a program have brought a discovery of major signiffcance. Parallel optical studies have led to the identiffcation of a few members of an entirely new class of astronomical objects; tìeir presence had been signaled by strong radio emission coming from discrete point sources in the sþ. On photographic plates these objects ìi '1i appeared to be like ordinary stars; t-hey have no resolvâble disk or extended '.t, structure, and are called quasí-stellar sources. The discovery that members r..i of the class have large redshifts showed that we are dealing with very ir distant objects tlat are radiating energy at an enorrnous rate. Calculations ¡ made from the combined radio anil optical data show that the rate of energy Ft release from these objects is ât least l0 times greater than from the brightest r.t normal galaxies known. Indeed, the total energy stored in the exploding i1 system is so high that there is now a considerable question as to the ade. ii quacy of thermonuclear energy to account for the phenomenon. Calcula- 'a tions show that the energy stored is equivalent to the explosion of a hydro- gen bomb containing one billion solar masses of hydrogen. It apþears likeþ that a new type of energy source is required, and specrilation favors a mechanism involving the ¡elease of energy stored in the gravitational ffeld of a coì'lapsing body. If a mass equivalent to 100 million suns is compresseil into a radius somewhat smaller than the distance from ttre ea¡tì to the sul, enough energy will be released from the gavitational ffeld to account for the quasi-stellar energy sources. Obviously astronomers are only now beginning to assess the implications of this discovery, which may have as great an impact on physical thought as the discovery of nuclear energy ot the expansion of the universe. More data of a kind that is diftcult to obtain are necessary to explore the possibilities openerl up by this discovery. The identiûcation of further sources to the optical limit of our largest tele- scopes must be achieverl; their calculated distances are so much greater than those of previously identiffed individual obiects that cosmological moclels ean be put to an observational test. The spectral-energy distribu- tions, redshifts, polarization, anil spatial distribution must be found. 8 Copyright © National Academy of Sciences. All rights reserved.

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The signals, both in the optical and radio spectral regions, are weak. o Unless largo railio antenna systems anil large optical telescopes had been ir available, the true natu¡e of tlese remarkable obiects would not have been d discovered; further progress in understanding tleir nature is absolutely rs dependent upon suficient access to such facilities' Enougb instruments of the necessary size are not now available to support an all-out attack, even on tfris one major problem, to say nothing of tlre other pressing problems now awaiti.ng solution. The quasi-stellar sources are an excellent example of the complementary rt natu¡e of radio and optical astronomy. New diicoveries by radio techniques e suggest follow-up studies by optical metliods, which may leail in turn ù to the recognition of previously unsuspected phenomena of great im' portance. :S d 's THE INADEQUACY OF PRESENT FACILITIES v s Similar inadequacies of telescopic facilities can be documented in observa- v tional astrophysics. Only a few examples need be mentioned. The study rli it 1 of stellar evolution, which leads to a knowledge of the ages of stars and the history of our galaxy, sufiers from lack of data at the faintest light levels that l: 1 can now be reached witÏ only two telescopes in the world, the Lick 120-inch t- antl the Palomar 200-inch telescopes. Studies of galaxies aie hampered be- cause too few ¡otation curves and mass values have been determined, v due to the demandi of other proiects on the few existing large telescopes. Ð. I Optical measuremerits of polarization of radio sources carìnot be carried on l at a rate commensurable with minimum progress ín the ffeld. The recent resurgence of interest in planetary astronomy, encouraged t by the space program, has created new demands on existing large telescopes that likewise cannot be met. Commitments to programs already in progress v have made it dificult for observatories with large telescopes to divert time s to ground-based re-evaluation of many palameters of planets and their r atmospheres, r¡/hich are of vital importance in planning vehicular missions to I points in the solal system. Nearþ every phase of observational astrophysics is hampered today because tle rate of glowth of new astronomical facilities has not kept pace with the increasing ilemanil for fundamental data' In optical astronomy, we are living largely ãn the legacy of tLe pas! using instruments haniled down to us from the era of private Ênancing. In radío astronomy, U' S' instru- Ð Copyright © National Academy of Sciences. All rights reserved.

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ments are too few in number and not powerful enough to accomplish tbe tasks demandetl of them. If astronomy is to progress, major new faciüties are needeil. After considering the present serious situation, tlis Panel proposes the construction of the new facilities in optical and radio astronomy diseussecl in detail in Sections III and IV. In broad outline, we propose the construc- tion of three maior opticâl telescopes of the 150- to 200-inch size, four inter- mediate-size telescopes (60 to 84 inches), a number of smaller instruments capable of important bright+tar research anil training, two maiol array' type radio teiescopes capable of high resolution, two large paraboìic stðerable antennas of tle 300-foot class, and a number of special-purpose radio ínstruments for the unique problems of great importance. THE RELATION OF GROUND.BASED AND SPACE ASTRONOMY The foregoing recommendations, discussed and documented in Sections III and IV, are io, o"* ground-based installations' What is the relation of these propose OCR for page 1
are: (1) tle detection of gamma- and X-radiation, which give evidence of 1e ultra-high-ènergy events; (2) tle measu¡ement of the intermediate ultra- es violet and X-ray spectra of the su¡r and stars; (3) the study of the absolute intensity of the zodiacal light; (4) the detection of the cosmic light from le the u¡¡esolved background galaxies; and (5) the bringing back of physical )d samples of the surface materials of the moon and planets. High-resolution c- lr- photographs may be obtained from less-expensive balloon-borne telescopes. It is importa.nt to realize, however, that these key data obtained from ts space vehicles will in many cases need to be supplemented by observations v' ic that can be obtained quickly and easily {rom the groulcl. Examples would Ínclude: ( 1 ) opticaì identiÊcatÍon of the objects tlat emit X-ray and gamma- se ray radiation on direct photographs, followed by detailed spectrographic studies; (2) observation of the energy distribution in ordinary optical wave- lengths of those stars for which extreme-ultraviolet data have been obtained, particular'þ those objects that show abnormalities; (3) galaxy counts to tÏe opiical limit of the largest telescopes to interpret the space data on the cos- mic light; (4) planetary studies suggested by space results, such as tem- perature mapping and high-resolution spectra for identiffcation of atmos- II pheric gases. If the capability for rapid acquisition of this back-up inforrna- tion does not exist, the space data will not be inte$ated into as rich or of complete a picture as is ottrerwise possíble. m Astronomy from the ground and astronomy from space complement :d each other. One provides the bulk of the data easily; the other provides )d certain key data, inaccessible from the earth, with commensurateþ great efiort. Each mode of observation sees a part of the universe in a difierent le wa¡ and therefore each must be exploited. :s. The cost of launching telescopes will be borne by the space program, le and since the cost will exceecl, by a large factor, any of the items contained l¡t in our recommendaüons, it is not appropdate to consider here the admittedly ?e huge problem of funding space telescopes. .4,n example of the costs is fur- lIt nished by the 36-inch telescopes now under construction {or the Orbiting ry Àstronomical Observatories. Each instrument will cost $60 millíon launched, rh and each is designed to last one year. Comparable numbers for a similar út telescope on the gtound are $0.3 million for the basic instnment and a life- k- time of at least 50 years. Even with a generous allowance for the greater )e eficiency of space telescopes arising from better resolution and the darker re sþ babkground, the mst of doing the same observations from space that )e could be done f¡om the ground is at least 100 times greater, Obviously, no observation that can be done from the grounrl should be done with a 1t r{ Copyright © National Academy of Sciences. All rights reserved.

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space telescope. These instruments must be reserved for observations that they alone can make, A proper balance in expenditures for space equipment and for ground- based instruments must be achieved if ashonomical lmowledge on all fronts is to be gained at an optimum rate. The Panel's. recommendations for new facilities are based bottr on the genuine needs of ground-baseil astronomy in its owri dght and on the equipment needed to adequateþ supplement the space program. It would indeed be urrealistic to concentrate support on the space efiort without corresponding attention to the requirements for terrestrial facilities. More gror:.nd-based telescopes are needed if neces- sary data are to be obtained with suficient speed at minimum cost. Our recommendations cover the next 10 or 15 years in ground-baseil astronomy. They are, in a sense, minimal. That is, for example, we ilo not recommend constructioà projects that technically could be carried out, such as a 400-inch optical telescope, though it would be of benefft to the science. We believe that the recommendations are ¡ealistic in terrns of what can be achieved within our present technology anil of what will be of most benefft from 1965 to 1975 anil some years beyond in the present wave of advance. If new facilities are not created, either tlrough private fulding or tluough government support, then gifted young astronomers will turn to other ffeldl tlre promise of astuonomy will remain unfulfflled, and .{merican astronomy ii will surely stagnate in this century. tl .:l 12 Ë- Copyright © National Academy of Sciences. All rights reserved.