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Ground-Based Astronomy: A Ten-Year Program (1964)

Chapter: 2 The Present Position in Ground-based Astronomy

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Suggested Citation:"2 The Present Position in Ground-based Astronomy." National Academy of Sciences. 1964. Ground-Based Astronomy: A Ten-Year Program. Washington, DC: The National Academies Press. doi: 10.17226/13212.
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Suggested Citation:"2 The Present Position in Ground-based Astronomy." National Academy of Sciences. 1964. Ground-Based Astronomy: A Ten-Year Program. Washington, DC: The National Academies Press. doi: 10.17226/13212.
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Suggested Citation:"2 The Present Position in Ground-based Astronomy." National Academy of Sciences. 1964. Ground-Based Astronomy: A Ten-Year Program. Washington, DC: The National Academies Press. doi: 10.17226/13212.
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Suggested Citation:"2 The Present Position in Ground-based Astronomy." National Academy of Sciences. 1964. Ground-Based Astronomy: A Ten-Year Program. Washington, DC: The National Academies Press. doi: 10.17226/13212.
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Suggested Citation:"2 The Present Position in Ground-based Astronomy." National Academy of Sciences. 1964. Ground-Based Astronomy: A Ten-Year Program. Washington, DC: The National Academies Press. doi: 10.17226/13212.
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Suggested Citation:"2 The Present Position in Ground-based Astronomy." National Academy of Sciences. 1964. Ground-Based Astronomy: A Ten-Year Program. Washington, DC: The National Academies Press. doi: 10.17226/13212.
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Suggested Citation:"2 The Present Position in Ground-based Astronomy." National Academy of Sciences. 1964. Ground-Based Astronomy: A Ten-Year Program. Washington, DC: The National Academies Press. doi: 10.17226/13212.
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Suggested Citation:"2 The Present Position in Ground-based Astronomy." National Academy of Sciences. 1964. Ground-Based Astronomy: A Ten-Year Program. Washington, DC: The National Academies Press. doi: 10.17226/13212.
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Suggested Citation:"2 The Present Position in Ground-based Astronomy." National Academy of Sciences. 1964. Ground-Based Astronomy: A Ten-Year Program. Washington, DC: The National Academies Press. doi: 10.17226/13212.
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Suggested Citation:"2 The Present Position in Ground-based Astronomy." National Academy of Sciences. 1964. Ground-Based Astronomy: A Ten-Year Program. Washington, DC: The National Academies Press. doi: 10.17226/13212.
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Suggested Citation:"2 The Present Position in Ground-based Astronomy." National Academy of Sciences. 1964. Ground-Based Astronomy: A Ten-Year Program. Washington, DC: The National Academies Press. doi: 10.17226/13212.
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Suggested Citation:"2 The Present Position in Ground-based Astronomy." National Academy of Sciences. 1964. Ground-Based Astronomy: A Ten-Year Program. Washington, DC: The National Academies Press. doi: 10.17226/13212.
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Suggested Citation:"2 The Present Position in Ground-based Astronomy." National Academy of Sciences. 1964. Ground-Based Astronomy: A Ten-Year Program. Washington, DC: The National Academies Press. doi: 10.17226/13212.
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Suggested Citation:"2 The Present Position in Ground-based Astronomy." National Academy of Sciences. 1964. Ground-Based Astronomy: A Ten-Year Program. Washington, DC: The National Academies Press. doi: 10.17226/13212.
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Suggested Citation:"2 The Present Position in Ground-based Astronomy." National Academy of Sciences. 1964. Ground-Based Astronomy: A Ten-Year Program. Washington, DC: The National Academies Press. doi: 10.17226/13212.
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Suggested Citation:"2 The Present Position in Ground-based Astronomy." National Academy of Sciences. 1964. Ground-Based Astronomy: A Ten-Year Program. Washington, DC: The National Academies Press. doi: 10.17226/13212.
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Suggested Citation:"2 The Present Position in Ground-based Astronomy." National Academy of Sciences. 1964. Ground-Based Astronomy: A Ten-Year Program. Washington, DC: The National Academies Press. doi: 10.17226/13212.
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Suggested Citation:"2 The Present Position in Ground-based Astronomy." National Academy of Sciences. 1964. Ground-Based Astronomy: A Ten-Year Program. Washington, DC: The National Academies Press. doi: 10.17226/13212.
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Suggested Citation:"2 The Present Position in Ground-based Astronomy." National Academy of Sciences. 1964. Ground-Based Astronomy: A Ten-Year Program. Washington, DC: The National Academies Press. doi: 10.17226/13212.
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Suggested Citation:"2 The Present Position in Ground-based Astronomy." National Academy of Sciences. 1964. Ground-Based Astronomy: A Ten-Year Program. Washington, DC: The National Academies Press. doi: 10.17226/13212.
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Suggested Citation:"2 The Present Position in Ground-based Astronomy." National Academy of Sciences. 1964. Ground-Based Astronomy: A Ten-Year Program. Washington, DC: The National Academies Press. doi: 10.17226/13212.
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Suggested Citation:"2 The Present Position in Ground-based Astronomy." National Academy of Sciences. 1964. Ground-Based Astronomy: A Ten-Year Program. Washington, DC: The National Academies Press. doi: 10.17226/13212.
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Suggested Citation:"2 The Present Position in Ground-based Astronomy." National Academy of Sciences. 1964. Ground-Based Astronomy: A Ten-Year Program. Washington, DC: The National Academies Press. doi: 10.17226/13212.
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Suggested Citation:"2 The Present Position in Ground-based Astronomy." National Academy of Sciences. 1964. Ground-Based Astronomy: A Ten-Year Program. Washington, DC: The National Academies Press. doi: 10.17226/13212.
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Suggested Citation:"2 The Present Position in Ground-based Astronomy." National Academy of Sciences. 1964. Ground-Based Astronomy: A Ten-Year Program. Washington, DC: The National Academies Press. doi: 10.17226/13212.
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Suggested Citation:"2 The Present Position in Ground-based Astronomy." National Academy of Sciences. 1964. Ground-Based Astronomy: A Ten-Year Program. Washington, DC: The National Academies Press. doi: 10.17226/13212.
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Suggested Citation:"2 The Present Position in Ground-based Astronomy." National Academy of Sciences. 1964. Ground-Based Astronomy: A Ten-Year Program. Washington, DC: The National Academies Press. doi: 10.17226/13212.
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Suggested Citation:"2 The Present Position in Ground-based Astronomy." National Academy of Sciences. 1964. Ground-Based Astronomy: A Ten-Year Program. Washington, DC: The National Academies Press. doi: 10.17226/13212.
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Suggested Citation:"2 The Present Position in Ground-based Astronomy." National Academy of Sciences. 1964. Ground-Based Astronomy: A Ten-Year Program. Washington, DC: The National Academies Press. doi: 10.17226/13212.
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Suggested Citation:"2 The Present Position in Ground-based Astronomy." National Academy of Sciences. 1964. Ground-Based Astronomy: A Ten-Year Program. Washington, DC: The National Academies Press. doi: 10.17226/13212.
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Suggested Citation:"2 The Present Position in Ground-based Astronomy." National Academy of Sciences. 1964. Ground-Based Astronomy: A Ten-Year Program. Washington, DC: The National Academies Press. doi: 10.17226/13212.
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Suggested Citation:"2 The Present Position in Ground-based Astronomy." National Academy of Sciences. 1964. Ground-Based Astronomy: A Ten-Year Program. Washington, DC: The National Academies Press. doi: 10.17226/13212.
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that ¡nd- onts THE PRESENT POSITION new IN GROUND-BASED ASTRONOI,TT lmy ìent port ents ces- It is clear that ground-based astronomy has spread before it a wealth of inviting prospects. Questions of the most fundamental nature regarding med the structüe and evolutionary history of the universe can be asked with DOt reasonable hope of obtaining answers. But on one frontier after another uch the growth of knowledge is limited because we need far more extensive oce. obse¡vational data than we now have. rbe What new facilities are needed to exploit the opportunities? In arriving refft at a recommended program, the Panel has conside¡ed the existing facilities, oce. and has reviewed how they came into being and were brought to their ugh present state of operating eficíency. It has compared the technical capabil- tds, ities of existing proven telescopes with the requirements set by the observa- )my tional tasks now clearly foreseen, It has also considered a projection of astronomical manpower over the next ten years, to keep the facilities and the number of observing outlets ín step with the demands of a growing body of researchers, and yet not outrun the expected supply of experienced instru- mentalists and observers needed to build and operate t-he new major installa- tions proposed. The Panel presents here its evaluations of tìe present posi- tion as a background for the recommendations tÏat follow in Sections III and IV. EORET IC AL AST ROP HY SIC TH S Before éxtensive new facilities are recommended, it is necessary to ínquire whether progress in understanding the universe is not as dependent on interpretâtion of old observations in the light of known physical laws, and on the new ideas that may thus come from theoretical astrophysicists, as it is on accumulation of still more observations. In the earþ decades of the 20th century, when the highly successful mountain-top observatories in tle western United States were exploring the virgin ffelds laid open by the great new telescopes, it was perhaps tme that not enough time was spent t3 Copyright © National Academy of Sciences. All rights reserved.

on relating observaüons to theo¡etical lmowledge, The interpretations were not long in coming, but they came mainly from elsewhere. The founda- tions of modern theoretical ashophysics-theories of stellar atmospheres, the internal constitution of tlle stars, and cosmolog¡ for example-wãe hid in Europe, where cloudy skies anil small telescopes discouraged rapid develop- ment of observational astronomy. The Panel believes that any imbalance that may once have existed in this coultry has long since been co¡¡ected. At many universities in the United States tlere are groups of mature practitioners of theoretical astro- physics. Graduate schools give every young astronomer ín training a basíc grounding in the subiect, and at certain centers a number of studànts pre. pare for caree¡s in that field. Physical scientists trained in neighboring ûelds have become interested in astronomy and have made maior theoretica-i conkibutions to problems of thermonuclear energy soutces, to stellar evolu- tion, and to the radiation physics of radio sources, for example. Another desirable development has been the near disappearance of t}re separation between observationalists and theo¡ists. euite a number of U.S. astronomers are adept in both roles, and a balance in the numbers of spè- cialists of the two Çpes is maintained in most university graduate depart- ments. Through Irequent visitation and extended sojoìlrns at maior centets, the pure theoretical âshophysicists maintain fairly continuous contact with . :,1 the latest observational results, and there is immediate feedback of their ideas into proposed new observations. The Panel concludes that progress in observational astronomy is not idealimited. The limitation is still well on the side of obsewations, which come much more slowly than the flashes of insight that may be their initial ilspiration. While the Panel has concentrated its attention on the facilities needed to accelerate the acquisition of new observatíonal data about tÏe universe, it also recognizes the great importance of a continuing buildup of strength on the theo¡etical side. OPTICAL ASTRONOMY Present Domínant Position of the UníteiL States The position of Ieadership that thd United States enjoys in optical astronomy has been won as a direct result of its superior observing facilities. The event of greatest hístoric signiffcance was the building of the S6-inch refractor T4 Copyright © National Academy of Sciences. All rights reserved.

at Lick Observatoïy on Mount Hamilton in the 1880's. This was the ffrst rtions permanently occupíed mountain observatory anywhere, anil quickly demon- unda- itt"ted t¡" advantages of such a site' The greât success of tle 36-inch tìe s, Crossley reflector at Lick Observatory a few years later leil naturaþ to ricl in tle perfecting of the large modern reflecting telescope, with all its advan- 'elop- tages for askophysical research. The founding of the Mount Wilson Ob- seivatory witl its 60-inch reflector, completed in 1908, and its 100-inch in :ed in 1918, was perhaps the decisive step towaril achieving leatlership. It was n the not entirely a matter of size and superior atmospheric conditions, however. astlo- The insistence of tle builders of all these pioneering telescopes on the high- basic est sta¡dards of optical and mechanical performance also contributed to ¡ pre: their spectacular success. The McDonald 82-inch telescope in West Texas oring in 1939, the giant 200-inch reflector on Palomar Mou¡rtain in 1949, and the etical 120-inch reflàctor at Lick Observatory in 1959 complete tìe list of tle rvolu- telescopes that have continued ttre tradition. All save the last were private grftr; th" 120-inch was ffnanced by tax monies of the State of California. rf the Íhese great telescopes are the peculiar American contribution to the devel- : U.S. opment of asbonomy. Inshuments like them are so essential to astronomers I spe- tlat nerv large telescopes are being planned in other parts of tÏe world. )part- À 104-inch reflector at the Crimean Observatory in the U.S.S.R. is iust get- nters, ting its auxiliary instruments, and a 237-ínch for a mountain site in the with U.S.S.n. is being planned. A 150-inch reflector for the Southem Hemisphere their is beíng planned by a group of European countries, and anottrer one of similar size for t}re Southern Hemisphere is being discussed by British s not Commonwealth nations. The momentum of the .{merican observatories will vhich not be quícHy overcome, but inevitable continuation of a position of leader- ¡itial ship should not be assumedl, leded i¡else, Thø Limìting Fa.ctor for Future Success rngth \ryith these excellent instruments in thè good-climate areas of tÏe western United States, what limits more rapid progress on the unsolved prob- lems already opened up? The Panel believes that it is not a lack of a unifying tleoretical concept or of new ideas, as explained earlier; not is it the lack of a proper number of skilled and imaginative observational âstronomers, It is not tÏe need to wait for crucial bits of data from space telescopes, helpful as these may be in certain cases. Neither is it delay in the con- nomy struction of a larger telescope than any yet made to get pâst an all-important event threshold of information. The limíting factor is, rather, simply the ertremelg actor t5 Copyright © National Academy of Sciences. All rights reserved.

smnll m.rmber ol telescopes of ad.equnte siza in d.ark-skg Incatians and, úrc l consequent slow accumulation of urgentþ needed observational data. Only : a handful of ast¡onomers can now be engaged in a sustaineil attack on fron- tier problems at any one time. This dilemma arises because astronomical soulces are so faint tlat tele- scopes of the largest size are required for at least part of most problems. If we compute tle output capacity of all telescopes with adequate light- collecting area now in operation any'rvherg and compare this with the crucial I problems requiring certain numbers of photon-hours for their solution, we immediately perceive that our present instrumental facilities are entirely inadequate to meet the astronomical demand. Thus data precious to the advance of astrophysics are presently denied us. Only two existing telescopes are adequate for pushing current frontier problems to the observational limit. These are the Lick 120-inch and the Palomar 200-inch reflectors. (The 100-inch telescope on Mount Wilson has lost efiectiveness because of the light from nearby metropolitan areas.) These two telescopes do not begin to satisfy the requirements of mid-2Oth century astronomy. Experience over the past 20 years at the McDonald, Lick, Mount Wílson, and Palomar Observatories, shows that the most effi- cient exploitation of large telescopes requires carrying on several programs at once-work on faint obiects at the photomehic limit during the dark of tle moon, and spectroscopic work during moonlight. There is, however, an optimum number of perhaps 10 long-term problems that can be handled at any one time-giving each of them about 35 nights a year. Even then, such problems as t-he distance scale of the udverse, where cepheid variables must be found and measured. in galaxies, require.two to four years to com- plete at tlis rate, because of the large number of plates required. This means that 10 to 15 stafi astlonomers per major telescope is all that can be efiective. With onþ two major frontier telescopes operating, this means that no more than two or th¡ee astronomers in tTe entire worlil now have the opportunity to work on the most excitíng problems in any given ûeld. Competition and the obviously needed opportunity to check results are lacking. The problem, serious enough from the standpoint of progress, is even more serious in another respect: it squeezes out of research life at the frontier top-notch men who, by accident, are not among the fortunate staff members of big observatoríes. This is an extremely unilesirable situa- tion from many points of view. The problem can be, and is, documented every month by the adminis- trations of both Lick and Mount Wilson-Palomar, where meritorious projects 16 r-_ Copyright © National Academy of Sciences. All rights reserved.

bv competent "outsicle" astronomers must be fumed down time after time il the fár hck of guest-investigator time at tbe telescopes' Ooly The establishment of the Kitt Peak National Observatory will begin to fron- ease the problem, but it is so acute that tÏe establishment of only one more 50-inch) is ot a sufficient answer' This is partþ -rio, t"i"r"op" (the 1be the only non-private instnment available to the tele- : because Kitt Þeak will n ,lems. more thnn 700 obsørcer canÅ,íilntes' ( Neither the Lick nor tle Mount Wil- IiCht- instítutions, ancl ,on arrd Pulomar Observatories are federally supportetl rucial thei¡ instruments are not generally available' ) If the yearþ assigned observ- n, we ing ,i*" on any large telescope is cut below 15 niqhts p3r proiect, no real tirely mã¡or problem'can be completed successfully in less,than three or four o the .,""r.. *hi"h is extremeþ long by modern standarils' There will, of course, L" i"* spectacular onå-shoi discoveries made with only a few nights, but rntier th" "follo*-ìp of these leads, so essential in the orclerly, progressive advance tl the of astronomy, will be missing. /ilson The inádeq-uacy of the existing large telescopes for the difficult prob- :eas,) lems involving fãínt sources would be even more acute if telescopes of lesser i-20th size could ,to-'t b" used to câlry the considerable fraction of the needed rnald, observations that do not demanil such geat light-gathering power' Tele- t efi- scopes of intermediate size can perforrn all the standard- observational tasks ms at ove-r most of the brightness range covered by obiects of a given class' For ,i thu some types of measrirement, toãh ut the study of nebulae, there is almost )f, an no loss of efficiency in going to a quite motlest telescqpe' ndled of the most productive use of Recent astronãmy it t"pl"t" *ith then, "*amples telescopes of small and intermediate size. Examples are: (1) photoelectric iables photometry of hundreds of sta¡ clusters to iletermi¡e color-magnituile dia- com- g."-., (2j the study of the rotation of galaxies from- spectrographic r-adial This ielocities, (S) spectroscopic studies of physical conditions and abundance an be ratios in gàsåous nebdaã, (4) the study of intrinsic variablg stars a¡d neans eclipsing iinaries, ( 5 ) narrow-band ûlter photometry for determining have lumlnosity and chemical composition of stars, and (6J obiective prism ûeld. suruey, fó, the discovery of peculiar emission obÍects and t-he iilentiffcation s are of stars of a particular class. gress, Interest L these valuable lines of research has maintaineil a steady ife at pressure on telescopes of small ancl intermediate size, which has been unate ànly pa*ly relieved b'y the facilities alreacly completecl at the Kitt Peak situa- Ñ"íi-"t óbservatory. The inadequacy so strongly felt at the largest tele- scopes is equally critical all along the line, and plans to bolster observing ninis- poiu, by U"lai"g new telescopeì must give attention to the whole range oiects t7 Copyright © National Academy of Sciences. All rights reserved.

of sizes in order to provide an eficient set of observing tools tailored to the varied obsewational needs of the astronomical community. RADIO ASTRONOMY PÍesent Posítiøn of the United States The United States now has an impressive group of major radio telescopes; contrary to the situation in optical astronomy, however, it can not be said that the Àmerican position is dominant. The ûrst line of American tele- scopes, all constructed in the recent past, includes three large telescopes: the 1,000-foot ffxed-mirror irìstuument at .,{recibo, Puerto Rico, the 300-foot paraboloid at the National Radio Astronomy Observatory (NRÀO), and the 600-foot cylindrical paraboloid of the Universíty of lllinois; the latter two are tuansit instruments. Then there are the two-element interfetometers at the California Institute of Technology anil NRAO, and the soon-to-be- completed, 140-foot, fuþ steerable radio telescope at NRAO. As power- ful as these i¡strûments are, they are exceeded in capability (in ways to be discussed later ) by such foreign instuuments âs the 2l0-foot telescope in Australía, tÏe 22-meter millimeter-wave telescope near Moscow, and ttre large cross-q4)e arrays nearing completion near Sydney and Moscow. A {urther development that will outrank American telescopes in capability is tlre proposed high-resolution instrument to be constructed by the Benelux nations. for Hàgþ Angulnr Resolutian NaeiL Even more important than the capabilities of U. S. railio telescopes rela- tive to tlose in other parts of tlre world, however, is the capaciÇ of these telescopes to provide the key data requirecl by the central problems now confronting radio astronomers. In one ffeld of research after another, existing and projected telescopes fall short in one all-important respect: angular resolution. The reason for the exceedíngly |uzzy view o{ the radio sþ given by these instruments is that they are not large enough, measured in units of the wavelength of the receíved radiation, to narrow the instru- mental diflraction patter:n to efiective levels. It must be remembe¡eil that radio telescopes difier f¡om optical telescopes in their ability to resolve ûne detail because the wavelengths of the radio waves are as much as a million times longer tlian the wavelength of the optical railiation. t8 t_ s Copyright © National Academy of Sciences. All rights reserved.

opes; , said tele- opes: )-foot , and r two retels o-be- lwef- ys to scope , ?nd scow. .bility 7 ¡elux The peculiar galary tr482 in hlJd,rogen light. Thø frLaments eúend,íng upøard and Fíguîe are composeð. ol nateîial tlxrolÙn oltt bg an erplosion in tlle nuclear regioñ of the dotL;nuaard, galaq about I milliþn geo.Ìs aga. rela- these ; now other, rpect: radio !sured nsfuu- I ttrat 'e ûne lillion É. Copyright © National Academy of Sciences. All rights reserved.

r Fígure 2 The spiúL galaxg M31, uíth íts tüo compaìnioß, as photogruphed þith øn optícøl telescope giDíng a rcsolu- tion of 1 second, of arc- iJ- Copyright © National Academy of Sciences. All rights reserved.

The galarg M31 øs ít u;ould, appeu to a lelesaope 4 ¡esoluÍían ol 34' The gaünV M37 Fìgure seen tD¡th 12, resohttìon- o.s L íts tØo aompaníons, ,ope eíþíng ø rcsolu 5 galatg M31 as seen aith 3' resolut¡on- 6 Th.e The galary M37 as seen @ìth ft Figurc rcsolutìon. Copyright © National Academy of Sciences. All rights reserved.

8 The spiîol golLxg M87 os seen Ðilh 7' rcsolutíon' Fìs|iîe galarg M87 as seen aíth an optícal 7 The l)71n, tio" tttot pott¡ble Øíth er'islìñg rcilìo relescopes spìto¿ Fìeu¡e telescope gioíng 7" tesolution The uhbþool galary as seen 1þith 7' resohiìon' The whi pool ¿alaxg,M51' as seen þith an optí' 9 Figure gioìn! 7" resolulion' cal telescope i I- l Copyright © National Academy of Sciences. All rights reserved.

seen tDíth 7' xs ting tad,io t el¿sc opes. 12 Thé bared spi¡al gala*g NGC 1300, a's seen Th.e barred' spâ¡al' gala*E NCC 7300' as seen r-igute 11 of existirl! radío Loith 7' lesolution, begond the cøpabi\ta optícal telescope giDing 7" rcsolutìon telescopes, Copyright © National Academy of Sciences. All rights reserved.

Figr.ue 14 The model skg of Figure 13 as it Lþoul¿' be 13 A s(nlple of si,mulated' sk{ populated @ith tun- FígØe seen at a rcsohttion oÍ 7', or about th&t possìbtø @ilh a d,ontfu d.ístrtbuted. radìo soØces of a consíderøble tunge ol 300-foot tudio telescope üorkiltg at 2f cm. ifltensífies, seen under híeh resolution. The area shoøn cott- tains about 70 squ rc degrces. L I Copyright © National Academy of Sciences. All rights reserved.

Fl,gurc 16 Th,e modd skg oÍ Figure 13 at a îesoh.ttt'n of ít toould, be The model skg of Fi,gute 73 at a resohttioí of 3' aà oossíble üíth a 7', begond, the capabllitv of ang eíìsting rudia telescopes. Copyright © National Academy of Sciences. All rights reserved.

Thus the maior factor that limits the advance of rarlio astronomy today is not particularly lack of obsewing time with frontier instruments, as in the case of optical astuonomy, but rather the lack of instuuments oI the proper design to meet problems no\M recognized. Two important facts should be recognized in an analysis of the Ameri- can-and tÏe world-wide-program in radio telescopes: I ) None of the pro- posed or existing instruments will provide the versatility, the speed, anil particularþ the resolution demanded for substantial progress with tÏe prime astronomical problems. The only ínstrument that approaches the require- ments is the proposecl ântenna system for the Califomía Institute of Tech- nology; its limitations are tlat its resolution is not su.ficiendy good, its energy-collecting area is limíted, and its sídelobe levels are high. Thus it may reach only the strongest sources efiectively. The resolving power of all the other existing instruments falls far short of the requireil speciffcations. 2) Conùary to the situation in optical astuonomy, railio telescopes have not yet nearly approached the ultimate limitations in performance produced by intromogeneities of the eaïth's atmosphere. Theory anil preliminary experiments have indicated that the ultimate aknospheric limitations on radio-telescope resolution will be about the same as tltose for optical tele- scopes-a fraction of a second of arc. Thus, there is no natural barrier that prevents building radio telescopes on the ground witl an angular resolution far beyonrl tlìat yet achieved, and thus to go beyond an all-important threshold of information. Tuming now speciûcaþ to the problems presented by existing radio resolution, we demonstrate graphically the efiects of this resolution tluough the presentation of actual photographs of celestial objects made with a resolution simulating that of radio telescopes. These photographs were prepared by Dr. J. S. Högbom at Leiden Observatory, using optical plates from tle Mount Wilson and Palomar Observatories. In prepäring these illustrations, a technique is used in which high-quality optical photographs, which have an efiective resolution of a few seconds of arc, are reproduced with an out-of-focus enlarger that simulates accurately the performance of a radio telescope of interest. Resolution of Ra.dio Galnrìes The loss of detail in viewing a nearþ galaxy is shown in a series of pictures made by the above proceilure. A standar<l photograph of the giant ipiral galaxy M31 is shown in Figure 2. Its optical image has a major axis of about I 5! Copyright © National Academy of Sciences. All rights reserved.

see the galaxy as it would appear to a telescope with 180. In Figure 3 we value given by present 85-foot telescopes at 21-cm wave- 34' resolution, a length. It is obvious that at this resolution all detail disappears, except for the flatteníng of the galary. More alaming, the image of the small elliptical galaxy near M8l merges with the image of M31, giving tÏe illusion t¡.at M31 perhaps possesses a iet of radiating material. Such structu¡es actually occur in some very abnormal galaxies, and so it is very undesirable that an efiect such as this may appear spuriousþ. Figure 4 shows tle galaxy as seen with 12' resolution, about the resolution of the 300-foot telescope at 2l-cm wavelength. Still most of the important spiral structure of the galaxy is indiscemible, and Doppler studies of the rotation of the hydrogen gas in the spiral arms can give only a blurreil picture of the motion. Figure 5 shows the galaxy with 3' resolution, about that obtâinable with the 1,000- foot telescope, were it able to reach the declination of this obiect. á.t this resolution, important detail begins to appe in tle outer part of the obiect, but tÏe important nuclear regions remain unresolved. Finally, in Figure 6, where the resolution is 1', a clear picfure of the nuclear stmcture is begin- ning to appear, and there is hoþe that a clear observational picture of the physical structure of this object could be obtained. Yet no existing tele- scope can achieve this resolution. Equally discouraging is the fact that this is the galary of greatest apparent size in the northern sþ' To gain a clear underitanding of the structure of the various forms of galaxies in thè ll universe, a large number of more-distant obiects must be observed, anil a resolution of the order of seconds of arc will be required, Examples of the difÊculty in observing more-distant obiects are shown in Figures 7-12. Figure 7 is a photograph of the galaxy M81, whose major ;lli,. axis measures about 20'. Figure 8 shows the galaxy as it would appear at ;l the presently unavailable 1'resolution. Much important detail has been lost. ,.r, Figure I is the famous Whirlpool nebula, about I in diameter, and Figure 10 is its image with a 1' resolution. Its true form is only barely discernible, and the structure of the nuclear regions is lost. Figure 1l shows the barred spiral galaxy NGC 1300, and Figule 12 its image agaín with a 1' resolution. È-ìr Such ã radio picture, standing alone, might well be only a controversial enigma. :ï $ tì Resolution and the Cosmologi'cal Problem ,$ The important role of resolution in radio astronomy is nowhere more clearly Ì demonstrated than in radio observations associated with problems of cosmol- 20 i:i -81- Copyright © National Academy of Sciences. All rights reserved.

Itis now well established that moilerate-size radio telescopes hav-e ogy. 'ith sthci.ot sensitiviÇ to detect numerous radio sources even at the bou¡ds .ve- of the observable universe. Thus, in principle, the changes in mrmber, ept density, brightress, anil spectrum of these sources can be examinecl over rall the vast eons of time spanned as we look to such great distances' From ion such studies, the history of the universe can, in principle, be determined' Lles However, this can be accomplished only if we can see the most distant .ble sources clearly, which is to say that the telescope resolution must be sufffcient axy to distinguish well the most distant sources from oire another and ftom )pe ,r"uru. ro-*""r. It can be calculateil that this requires the clear resolution of the all radio sources when the total number of sources visible in the whole gen sþ is about one million. ufe Figure 13 shows a sample of about 10 square degrees of a simulated r00- sþ poslsessing in all about one million sources ilistributeil randomly' Figure this t¿ ,iro*t thiJmodel as it appears with a ¡esolution of 7', ¿ little better than ect, the resolution of the 300-foot telescope workíng at 21 cm, and the resolution ?6, of most existing 85-foot telescopes at their shortest opeÏating wavelengths' Iin- It ís obvious thãt ,ton" of the fainter sources can be reached at all with such the resolution. Fígure 15 shows the model as seen with 3' resolution, about that ele- of the 1,000-fòot or 140-foot antennas, each working at the shortest wave- hat length túat its accuracy perrnits. The picture ofthe sky obtained is still quite na inaãcu¡ate. ,A' striking fãature here is the high frequency with which appar- the ent double and multiple soulces appear spuriously' Double sources appear da featirre of the real radio sþ, so a spurious prodtiLction of to b" u "o-*on them is an extremeþ serious defect in any observing instrument' Lastþ, rwn Figure 16 is a view óf the model with 1' resolution, presentþ not available' rior O;ty at this resolution is a clear rendition o{ the model beginning to appear' rat Hoi.rrer, close comparison between Figures I3 and 16 shows that further ost. resolution will be reqired if a tr.uly accurate reproiluction of the model is to ure be obtaineil. In actual fact, it can be calculated that a resolution of 3Û' or ble, better is required to produce a pictùe adequate for cosmological computa- red tions. Cleaily, from ìhe preceding figures, no deffnitive krowledge of the ion. radio sources'throughout the universe can be obtained until ¡esolution of the sial order of seconds of arc is available to radio astronomers' Melhods of Achíeoing High Angulat Resolution of the Increased resolution can be obtained only by increasing the linear size trly to build a single antenna that Fortunateþ, it is unnecessary 101- "ri"nr",y.t"-. 2L iì Ë 8,, Copyright © National Academy of Sciences. All rights reserved.

fflls the complete area spanned by the most distant compolents of the sys- give the a*.ìLput"å, relativeb small ant",,nas spaced on a-Iong baseline necessafu'pattern of hígh resolution witì a small total area' -- Á Éà" e*ample-of this approach is the Mills cross in Australia' in *fri"n u- hrg" nu-Ë", of simple-dipole energy collectors are spaced out on il;"I¡ndï th; pattern o{ i "roti; io the sirnilar Ch¡istiansen cross' small p"ru'boloid, ,"""ivô th" urr"tgy. The wiilely spread energy coilectors are con- of '""","a so that thã perfo.-"o"L i*itat"t well the performance "f""oi""ly of us greit tlimension as the largest dimension of the ,"fl"cto, "ì*pi"a" " -,iooth"t - cross pattern. advance is the development in England of a scheme Ior using two-element interlerometer antenn¿s on a variable baseline in such a man- the electuical perform- ,r"" tUut, after many observations at clifierent times, ; co*pl"t"íy ffIlecl aperture of greai dimension- can be imitated' or ;;; ;.yott interfeiometer expedments have brought great atten- "ri""d."-fhesehat any distribution of radio sources, or radío "bright- tiáo to tttu concept t be represented as an infinite Fourier series of intensities ,r"r." in th" tþ, í"u"I".tgth, projected on the sþ' An interferometer' at âny ""n "iïUlp"i*f ;J;f; recording oã" of thlt" Fourier components' Given time' ynthesis enough ;;;;;;;" can b""obtuio"d to allow a combination in.a Fourier s th"i ."p.od.t"", with good accuracy the appearance of tle raclio sþ' It now tÏe o this technique õp""i aft"r, if sufficiãnt care is tafenrwith mapsbservations' The procedure of tÏe sky' froa,r""'"""*ate high-resolution ailio vilgor in England and at other places' It becomes evi- "ãå i, biog prttuud with ã"", i.?å any careful slucly of thL aperture-syntlesis technique' however' that the procådure is a very lengthy and teilious- one; fu¡tlermore' when a - where ex- larse ,ro;ber of Fourier compoients are needed, as is the case it"it" ."r"1",i"" is required, ii b""o*"t very difficult to maintain suficient the Fourier accuracy in tlle measurement of the phases and amplitudes of com'onents' A compromise solution to the problem is to use many rerceiving elements simultaneoirsly, so that many Fourier comporr"ttT ut" received simultane- components to be ;"rto À iudiáíus choice cán be maile of tÏe Foufier in ,u""i,r"il,'.o that the prime astrophysical in.formation about the source q";.tiá; rt emphasizeå. The ¡esuli is a rapict acquisition of data' and a sys- i"- io *lti"ft e^rrors in phase and amplituãe âre more easiþMills and Ch¡is- discovered-and corrected, Ieading to acceptable accuracy in the results' The ai'e, in faci, examples of this procedure' It has become clear ti"rrr"n "lt" ,eqoired resolutions åf f"* secónck of arc are to be obtained .orr", il t tlr"t, " 22 ,-L Copyright © National Academy of Sciences. All rights reserved.

with tìe ffrrancial and tecbnological resou¡ces realistically presumed to be available, this indírect but efiective procedule must be used, Rapid steps in this direction a¡e being taken. Examples are the construc- tion of the 1.6-lqn cross of the Universþ of Syilney, now nearing comple- tion; the l-lar¡ cross nearly completed by the Lebeclev Physical Institute, Moscow; the l-kn cross of the UniversiÇ of Bologna; anil the new aperture- s¡mthesis ínterferometer of Cambridge University, Extensive experience in aperture-slzrthesis techniques eústs in the United States; one of tÏe out- standing interfe¡ometers is tlat of the California Institute of Technology, which has given many young astronomers backgrounds in tlese techliques. Soon the long-baseline interferometer of the National Radío Astronomy Obsewatory will have given a new group of scientists experience in this ffeld. I Collecting Area and Sídelabes as L¿nxi,ti,ng Factors t- Two major factors besides resolution must be considered in evaluating )s radio telescope desígn: energy-collecting area, and secondary responses or v sidelobes ofi the main beam. The two are interconnected. h Secondary responses or sitlelobes arÈe from the fact that every antenna is collects a small amourt of energy from all parts of the sky. In certain direc- tions, this response may be an appreciable fraction of the response in the te main beam, i.e., from the ilirection the telescope is pointing. When the side- re lobe response from a strong source equals or overwhelms that from weak .i- sources in the main beam, confusion and error resulg since the receiver )fr sums all the ¡eceived energy. This problem is particularþ acute when only a two or very few antenna elements occupy the space between tihe extreme x- separation requireil for speciffed resolution; hence the need to reduce the nt so-called grating response by adding the many Fourier components previ- ET ously mentioned. One solution is to ffll Ín the area between the two extremities completely. Its This is done in the paraboloid, for which tÏe sidelobe trouble is negligible. te- The collecting area is enotmously increased and signals from weak sources be are lifted out of the backgrouncl noise present in all radio receivers. The in advantages of paraboloids for many problems, discussed in a later paragraph, i's- are well k¡own. But in achieving resolution dre area is wastefully used, since nd the resolving power goes onþ linearly with the aperture and the cost goes is- as the 2.5 power of the aperture. ( See Section VI and the Àppendix. ) As the )ar size increases, the engineering dificulties of holcling a precise parabolic shape in a moving System impose severe obstacles. The compromise of a .ed 23 lÉ!. Copyright © National Academy of Sciences. All rights reserved.

úansit instrument, in which the paraboloid moves only about a single east- west axis, reduces tlese problems somewhat, but limits the observations of a given obiect to a few minutes each day while it is passing through the north-south plane. ,4' ffxed-mirror system permits a still larger apelture at the price of restricted sþ coverage' For mapping and investigations of indiviclual faint radio sources scat- tered over the sþ, it is much more efficient to use multi-element arrâys arrangeil in the form of a cross. The¡e must be a carefully calculated balance between the energy-collecting area needed for a satisfactory signal-to-noise ratio on the weakãit sorrtc"s tliat are clearþ resolved, and the number ancl spacing of elements required to suppless sidelobes adequateþ. Too large a "h[-in factor" not only ìs wasteful, but also, in tle case of the paraboloiil, it actualþ brings so many extremely faint sources above the detection level tìat a larger. aperture increases the confusion between such sources by a factor greãter thao the capacity of the aperture to resolve them. The result is a "cðnfusion-limited," ratler than an "íntensitylimited," system On the other hand, too small a "ûll-in factor" means higher sidelobes and a limita- tion to brighter sources. The rieans of achieving balance between the three interconnected fac- tors of resolution, energy-collecting area, and suppression of sidelobes are now well understood and are being taken into account fur designs for radio telescopes now projected. Techniques have been developed for iilentifying and eliminating siclelobe responses, with less fflling-in of the total aperture- spread of the antenna system than straighüorward optical theory would re- qìir". By slightly varying the frequency, or by combining the signals from tir" ,rarió.rs cãüecting elements with an altered set of weighting factors, the sidelobe response can be changed wíthout afiecting the main beam appre- ciably, thus providing a means of separating spurious sources. Parabolíc Antewøs Critical as is the need for high resolution, complex arrays are not the com' plete answer. A balanced anil fully efiective program of radio telescopes wlll include fully steerable single paraboloids of the largest feasible aperture' There is a class of problems, as in the stucly of variable radio sources, galactic shucture, and Lhe polarization of railiation, tÏat tlo not require the highest resolution. Studies of the 21-cm line of hydrogen and other spec- tral lines, or any problems that require frequency scanning, are extremely difficult with arrays. Not only for these problems, but also in situations where 2A 1; &._ Copyright © National Academy of Sciences. All rights reserved.

a telescope is required to serve a heterogeneous group of observels, as at the National Railio Astronomy Observatory, a single paraboloiil has been for:¡d to be the best solution. Indeed, such an instrument can be operateil on widely difierent frequencies simultaneously, thus facilitating use of dif- ferent programs on tle same ilay without change of i¡strumentation. When o""erráry, instrumentation at the single receiving point can be quicldy changed and experimental eqrdpment for exploratory measulement conven- iently and cheaply attached. And, not the least in importance, ease of use and versatility make tle paraboloid ideal for gtaduate students, thus giving them personal f¡st-hand experience. From the foregoing discussion it is clear that straighdorward applica- tions of known technology could produce radio telescopes considerably superior to any now existing in the United States. The giant 1,000-foot tele- scope at Arecibo, Puerto Rico, may produce a resolution of a few minutes of arc, but has limiteal sky and frequency coverage, and a major part of its obserøng tjme ís committed to a program of geophysical stuclies. The 600- foot telescope of the University of Iìlinois is limited by its frequency cover- age.to resolutions of the order of 10' of arc, and as a bansit instnrment it cannot track objects across the sky. The National Radio ,{stronomy Observa- tory (NRAO) 300-foot railio telescope is also limited in its frequency and sþ coverage, and by its inability to track. The interferometers at the Cali- foinia Instiìute of Technology and at NRÀO ( consisting of two 9O-foot and two S5-foot antennas respectiveþ ) are limited by their small efiective col- lecting area, which restricts them to stuily of stïong sources, and by the speed with which they can acquire data. The compound interferometer at StanJord UniversiÇ, which forms a fan beam less than one minute of arc wide, is limited to less than a dozen sources. Soon the NRAO 140-foot telescope will be finished; it will achieve resolutions of the o¡der of a few minutes of arc at best. There also exist in the Unite¿l States more than a half-tlozen 85-foot- class paraboloids at various institutions' Àlthorrgh these serve well for certain classes of problems, they are too small to provide adequate resolving power and collecting area. In summary, then, the tremendous U. S. progress in recent years has proiluced a series of impressive insbuments for radio astronomy. Their use has clearþ indicated fairly direct paths to profounclly important information about the univetse. But none of the instruments now in existence anywhere or authorized for construction are adequate for meeting these challenges. The United States should proceed with production of instruments that will uoss the resolution threshold, lest we neglect one of the most signiûcant 25 i:: . h ft" Copyright © National Academy of Sciences. All rights reserved.

scientiûc heritages of our tímes, The proposals in Section IV look toward a construction program suficient to overcome the inadequacies we have dis. cussed here. THE DILEMMA OF THE ASTRONOMY GRADUATE SCHOOL IN 1964 Equally as serious as the problems arising from tle lack of large frontier telescopes is the cur¡ent situation conceming the instrumentation at gradu- ate schools throughout the country. The demand for grailuate astlonoÍìers is very high. Whereas 15 years ago the few new astronomers produced each year were suftcient to satisfy the immediate needs of that era, today there are not enough astronomers either to satisfy the demands of the space pro- glam or to keep pace with expanding university requirements. On the sur- face, present demand and potential supply might appear to be on tÏe way toward a satisfactory balance.. Graduate schools are now flooded with appli- cations in âstuonomy; enrollment is higher than it ever has been and is in- creasing at the unprecedented growth rate of 19 per cent a year. (See the l discussion of manpower, pp. 28-37.) But herein lies the problem: Of the 30 Ph.D.-granting institutions, only a hanclful-perhaps tluee or four-are well llr enough equippetl with adequate instruments to teach âstronomy and astro- ll physics in the manner required. Most departments possess equipment (small i'., telescopes, light detectors, spectuogrâphs, data-¡eduction instruments ) t]1at dates from approximateþ 40 years ago. These deparknents are now asked to train students in this modern era. A parallel task would be to maintain high-level research and teachíng departments of physics without nuclear , accelerators o¡ modern low-temperature laboratories; or to teach chemistry with only Bunsen burners and test tubes; or to teach molecular biology with- out electron microscopes ancl X-ray apparatus. The circumstances leading to the present lack of university research facilities in astronomy can easily be traceil. Before World War II, astronomy was an "ivory towef' subiect in the university cur¡iculum, Most astronomy departrnents were small, consisting of one or perhaps tv¡o men with very few students. Almost no university could justify the creation of research ' facilities fo¡ such a small fraction of its activity. There were a few institu- tions, however, that did obtain research equipment, either by gifts from interested outside indiviiluals or from enlightened administrations that 26 i:.ì t. M. Copyright © National Academy of Sciences. All rights reserved.

ïï I strongly supported small but active astronomy programs' These few schools then ãevelopeil into the only graduate departments in the Unitetl States that stressed observational astrophysics, and tley a¡e the schools from which most graaluate astronomers have emerged' Not only thes-e schools, but also schooli that wânt to stør, astronomy programs' face almost insurmount- able problems in the present era with its increased pressure for excellence. Except for a hantlful of radio telescopes, there have been very few major adilitions to tÏe equipment of the existing graduate schools for mâny years. Even mo¡e serious is the fact that most of tle newly created grailuate depart' ments have virtually no instrumental legacy from the past. This problem was recognized about ten years ago when the discussions leading tJ setting up tÏe Kitt Peak National Observatory anil the National Radio Astronomy Observatory were begun. If the Kitt Peak Obserwatory did not exist, the situation in optical astronomy would now be almost intoler- able. At present, some of tìe graduate-student pressure is relieved because students from any institution in the courìtry can use the national facilþ at Kitt Peak. But it is estimated that Kitt Peak can satisfy only 25 per cent of the total demand that will develop in the near future. Furthermore, there is a fundamental disadvantage in reþing solely on the national facilities. Faculty members and students must travel from their home institutions to distant places in order to collect material for their re- search problems. They then return to their own graduate departments to analyze t}'te data. It is usuaþ the case in all experimental science that, as insight into a problem develops, difierent data are required or new tech- niqies must be employed at intermediate stages in the research. It is dificult .meet this requirement unless the research facilities are constantþ at to hand at the home institution. The most efficient use of the telescopes at Kitt Peak and NRAO would be in the Ênal push toward solution of problems, after observational techniques had been thoroughly tested on nearby mod- ern instruments. Thus, the necessariþ limitetl period with a larger telescope and good skies for optical observers could be usecl far more productiveþ' it is the opinion of this Panel that a number of graduate schools in tÏe country should be supported in tlreir attempt to acquire moderate-size tele' scopes so tåat such a icheme of operation could be adopted generally' There a Iimit to tlie size of the optical telescope that can be iustiûed i*, åf "orrrse, in parts of the country with low percentages of clear nights' In tlre opinio'l of ihe Parrel, telescopås hrger than 48 inches should not be built in areas of relatively poo, *""|h"r. Ho*"u"t, ít is abundantþ clear from results ob- tainecl, íoiexample, at the Case Institute of Technology, the University of !t Copyright © National Academy of Sciences. All rights reserved.

t, Wisconsín, and the University of Michigan that telescopes of 24- to 4O-inch size can anil have contributeil enormously to tle progress of observational astronomy. The research of both faculty and students _at these institutions is of high caliber, and exempliffes what can be done under relativeþ poor sþ conditions. The existence of modern telescopes at individual graduate schools has many advantages. À healthy ,"s""r"L atmosphere is almost automatically f"culty and students alike. The equipment is available for "r""i"d stronoirical pioblems that could not be solved on an expeditiola,ry "*orrf many a basis at a nauonal fãciüty. Specíal work on novae' comets, planets, and the moon at certain unprediótable times requires obsewations thât could not be made at a national observatory huntlreds or even thousands of miles away' Any problem requiring close iurveillarce, such as those posed by irregular ]rarialle stars, eJipsirig binaries, int¡insic variables, and tìre radio emission of Jupiter, cannotie ãealt with away from home because the neecl is for ,"j"uiu,l obr"*"tions at selected tímes. Most importânt is the fact that most uniiversity-connccted astronomeïs are engaged in teaching and hence a¡e on students are' t-he campus for three quarters of the year. A'nil this is where the If maxiirum use is to be made of equipment, it must not be locateil hun- dreds of miles away, but must be easiþ accessible, not more than one hour's travel time awaY. MANPOWER We have now outlined the present position of optical and radio astlonomy with respect to the facilitiei needeil for an aggressive attack on problems awaitinj solution. There remains the important question of the balance l¡e- t*e"o tie creation of facilities and tìe number of astronomers that wiII be demanding observing time when the facilíties are completed' The a-nswer to this question cannot be given in hard bookkeeping terms' because the availability of facilities afiects the choice that young scientists l, make on whether to g; into tÌìeoretical or into observational astronomy' The for evidence we have cit-ed earlier in this discussion-the unsatisûed demand centeï and the desire of many univer- the telescope time at maior observing sity graduate departments for modern, locaþ based observing equipment- poLis to tlte current severe limitations in facilities' Fine new instmments ^o.rdonbt"dly do attract and inspire imaginative use by outstanding young 28 ,i tn Þ -,.. Copyright © National Academy of Sciences. All rights reserved.

lr ì ì LC scientists. Without allowance for such intangibles, the Panel has examined the growth rate in the number of asttonomels in recent years, anil has at- tempteil to set upper and lower limits on tìle nunber of U. S. astronomers a decade hence. The conclusion points to no less than a doubling in t}re next ten years. If the current rapid growth in graduate enrollment continues, the factor of increase may be as large as 2.4. Truiníng of As'tronnmers Comparcd to Ttainíng of Other Phgsical Scíenfists Astronomy is one of the smallest disciplines among the engineering, mathe- matical, and physical sciences. The annual proiluction of Ph.D.'s has been widely used as an index of the growth rate in these Êelils, The following studies contain material relevant to the present discussion: Doctorate Productíon in tJni,teiJ Statas Uniqersitíes. Ofice of ScientiÊc Personnel of the National Àcademy of Sciences-National Research Council, Publication 1142. (See also Phgsics Toil'ag, 15:21, 1962 for ilata on physics Ph.D.'s.) Comparìson of Eørned Degrees Aaarded 7907-1962 ttsith Ptoiectioru to 2000. Nàtional Science For:ndation Report NSF 64-2. lnoestíng án Scíentìfic Progress. National Science Foundation Report NSF 6l-27; also Report NSF 62-43. Meating Manpouer Naeds in Science ønd' Technologg. Report No. 1, Graduate Training in Engineering, Mathematical, and Physical Sciences, by President's Science Àdvisory Committee, Dec.12, \962. The semilogarithmie plot of Figure 17 shows the annual U' S. Ph.D. proiluction in astronomy, physics, and all physical sciences (ûrst two refer- ãnces above ) . It is apparent tha t ouer the long term +Áe country's astuonomy education system has not consistentþ maintained tÏe smoothed growth rate of about 7 per cent per year (doubling time, 10.2 years) that has prevailed in related ,ãi"n""r. The decline in the period 1935-4I may have been causeil by the paucity of ¡obs in astronomy at a time when the field ofiereil many fáwer industrial and government openings than were available to physicists' The Ph.D.-production rate is perhaps a less reliable basis for estimating tÏe U. S. wolking force in astronomy than in othei physical sciences because of the importani fraction of foreign-born, foreign-trained scientists in the group. Môreot er, there is good evidence that an appreciable proportion of ihe present astronomy force transfened into astronomy aftel Ph'D' training in o-ther disciplines, such as physics and engineering. Yet Figure 17 shows 29 Copyright © National Academy of Sciences. All rights reserved.

tl:l 'i ,l;l il rl i,. .t r970 1960 1950 r940 1930 1920 Fígure 77 sciences ùt the fJnitect States' Annual Ph.D, 11ro¿uctìott itu attÍonony and other Ttlrysical t i &_ I 1,u.. Copyright © National Academy of Sciences. All rights reserved.

steady growth at about 3.8 per cent a year ( l9-year doubling time) through all the lostwar years, including the I950's, when physics-Ph.D. proiluction was onã plateau. Since 1956, there have been signs of an upsurge that may lead to a much higher growth rate. Before exploring the implications and making a projection based on the best cu¡rent data, it ís of interest to con- sider alnother'index of research activity in astronomy to see if corroborative evidence exists. rdÀIt 89í PER Fígøe 78 the lntemational Astrononúcal Uniotu 7921-1963' Crouth of U,5. membetship ¡tu proiecte¿ to f972. tlw Infernatianal Astronomical Union (J. S. Membershâp ín Figure 18 shows the number of U. S' members in the International Astro- nomical Union (IAU) from 1923 to 1961. Membership in the IAU is univer- sal enough among established professional astronomers so that weighting in favor of [he intemational-minded is negligible. Yet the standards of member- ship are such that, at any one time, a number of young and productive ,"rã"."h"r* who make heavy demanils on facilities are not being counted' The membership ffgure is tìerefore lower than the actual force, presumably by a constant percentage in a period of stable growth. The enumeration is insensitive to fôreign birth and training, anil to transfer into asEonomy from initial training in another ûeld' The plot in Figure 18 shows a steady growth rate of-4'5 per cent per year ( iloubling Umã, fO years) from 1923 to 1955. The-tlree points {rom (The íSSS ìo fSO¿ Jrow a sharp ltptorn to a doubling time of nine years 1964 point is an estimate from the U. S. National Committee of the IAU, 31 lì -t þ B'- Copyright © National Academy of Sciences. All rights reserved.

tle impression gainedJrom the glowÌb based on nominations. ) This conffrms tìe American Astronomical Society, and from the rapid in membership of swelling of the astronomy graduate student population' Since the latter gives the most up-to-tlate irformation, it has been made tl-re subiect of a special study. . Graduate Stuiønt Populntion in Astrotwmg Depattments The current survey gïew out of a census made by W. E. Howard III for the 1962 Conference on Graduate Education in Astronomy, held at Bìoomington, Indiana. Material for this study was gathered by inquiries to the 28 clepart- ments listed in the brochure entitled "Careers in Astronomy," published in 1962 by the Committee on Education in Astronomy of the American AStro- nomicál Society, plus four new departments known to the committee' The replies on tìe .t,rmbets of students in the falls of 1957, 1960, and 1963, plus eaich deparunent's estimate of the 1966 enrollment, are listeil in Table 1' The totals, plotted in Figure 19, establish a growth rate within the graduate schools of 19 per cent a year (a doubling time of 4.0 years )' This is near-þ twice the rate attained or projectecl in related sciences A simple extrapola- tion predicts 2,590 graduate students in astronomy ín 1973 The ffrst efiect of this surge was a Þh.D. output of 30 in 1962, considerably higher than ìn any previJus year, but a figure consistent with the assumption that the ph.O.t should'be at least 10 per cent of the student population, with a three- year lag to allow for the fact that rapid growth means a hígher proportion of ginning graduate students. be - What it the source of this boom and how long will it continue? In the opinion of the Panel, some o{ it was a natural growth, stimulated by general among science-inclined undergraduates of the exciting derrelop- "i"."rr"r,astronomy of the postwar years, and fostereil by wise supplemen- ments in tary support of resåarch and instïumentation in many universities by federal A new anil strong influence came with the ffrst Sputnik in 1957 ancl "gá.t"iår. tÈe widespread interest in space that followed. Since a good part of the university-based space efiort is in special institutes separate from astronomy departments-often dominated by physicists, geophysicists, and engineers- thJ rapidly growing student population in the departmental tâbülation of Table ì reprãsents a broad spectrum o{ interests, and something like the tra- ditional pioportion of tlre students may be expecteil to go ínto ground-based observational astronomy. The new astronomy students irndoubtedly lepresent a shift in interest Copyright © National Academy of Sciences. All rights reserved.

7 THE NUMBER OF CA.NU ATE STUDENTS IN ASTRONOMI TABLE BY INSTITUTION 1966 1960 1957 1963 . (nxrncrao) 22835 Untuersitu ol Arízona O 19 22 CaliÍorûia. In'stítute of Tealnolagg 35 16 35 23 tlnÍaeîsítv of CøInÍoîrìa, BØkelea 65 20 28 20 Unìoeßitg oÍ Ca.UÍomùt, Los Angelzs 40 3 51720 Case htstitute of Techrølogv 1 71420 Uítueîsftv of Chí'cago 6 641 Unioeß¿tg of Chûìnnati 0 42 I5 Uflioeßìtg oÍ Colþru¿o 50 7 5412 Columbíø UûbeßìtlJ 5 Uníoeßítg 2 Conell 01220 Florìdø Unbetsìtg of 0 40 31 Georgetoün Un oeßtfg 45 22 40 28 Haroard Uníoeßìta 55 24 813 Utuloeßìtu oî lllítuois 17 2 25 23 30 Indí.anafJnìaersítE 16 0610 Iotþ4. State Uníaeßitg oÍ 0 026 Un¿aeßitg O Louí9íøna Sta.te 22555 Ilntuersüg of Marllønd 0 32 28 Untuersttl! of Mtch¡'gan 76 40 011 NorthØestern uníoeßìtg 15 1 71425 Ohio St tte Unheîsìtu 5 81520 unìoeÍsifv ol Pennsgh)ania 3 6710 Pr¿ncehn Aníþeßíig 6 r8-13 RensselnetPolgtechn¿clnstitlûe 0 228 tJniÐeÌsitg oî Roch¿ster I É712 Stanford Unloeß¡tg 5 51225 ' Unioersitg of Terns 0 026 Vand.erbilt Uû¡þeßítg 0 o2L6 l Uniþersítg oÍ V¿rginial 2610 Wesl.egafl Uníoersitg 0 19 14 Uníoersitv of Wbconsín 30 2 62840 Yalþ Uníoeßíta 5 Totals within the 25 per cent fraction of the physical-science doctorates thai have been going into astronomy, physics, and geo-scien ces (Doctorate Production ín Uãitel ffiates Uníoersitíes, see p. 30). This percentage has remained stable over many years, as has the over-all fractíon of abdut one sixth of total doctorate production going into all the physical sciences' The shift diil not need to b; a hrge one to produce the drastic increase in astronomy alone, since astronomy plt.¡.t irr the years 1957-62 were only 3 per cent o{ t'hose in physics, rising to just over 4 per cent in 1962. An íncrease of the astronomy Ph.D.'s to 8 pei cent of the physics production, as was the case in the pre- nuclear decaãe of the 1920t, or even to 10 or 12 per cent, woulil not be Copyright © National Academy of Sciences. All rights reserved.

UNIFORÀ{ CROWTI¡ / , :¡ÀPERED GROWTII NUIIIER OF ASTRONOI4ENS GB¡.DUATE STI'DE\TTS I]NIFOR}I CNOWTII , 19ø PER YE,lû TÀPERED GÂOWTII 7 ¡¡n va¿¡ n¡ 1973 Fígurc 19 Ninnbet of gra.Iuate st¿(lents í'n asftonontg, the number of PhD"s 1954-1962, and Prcìecte¿ Ph.D. prcductíon an¿ total nuñl)et of \stronomeß to 7973' I l I I I L-"- Copyright © National Academy of Sciences. All rights reserved.

emphasis among the physical -sci- tantamount to a drastic redístribution of when o{ astronomers is stilitlisproportionately small ,¡" ;ö;ä ;the"*¡er manpower in physics' geophysics' and " total "î"ärï"" astronomv combined. """^îîãrå"r be support for increas- a" tustain a high growth rate there must National Defense Education Act is t-.,;;;; of øraduate ,úraÉots' The in a1l the phvsical sciences' and the efiect Ïiäil"ff;.'"i;"ì"pìr"'i""itt maximumpáint' The new National Aero- ;ililåå;;"i vet '"""h"d supportetl Administratiãn iN¡'s¿') i"16ç5hip- ^program and 886 fel- iäöä.ii;;r;ãJ. i" il n"1'{' ii" r0 institutions tur1s62-63' sources' to "",îu"r- ""Jóp"""' to nsease' according to- NASÀ it is expected lows in 1963-64; rn view of the announced pur- ;îi;;;*'t; as 4,00ô graduate students' fraction of the recþients could be assumed' :::ili1Ë;s;;;;*i" *ho *ot'Id otherwise have go, e into some other ;;;il;r*¿""" í""il this influence could accel- ;hy"*üì;;;;. ,{ltho'tghnitis conceivable that high ffgure' it is probably p'"'"nt very erate the growth late even "yoJ th" Ñns¡' fellowships mav be not safe to attempt such " p;;ñ;ti"";*' rhe cur- o"" ofthå sources of support that will sustain the ;;;ã,;";"d ", of inte¡est in astronomv in the universities' ;';;;";;;;n""sion A Ten-Iear Proiectíon in the Uniteil States will be Two projections of the number of astronomers growth rate in It may be assumed that the 19 per cent a;ear long enough to "aì"nñ,"d. truduáte-st.'ilent pàpuìation- has-bee¡ in efiect äsiffi;; long as the growth rate is sustainetl' achieve a new equilibtitt"', "íã'tttui, "s at u 19 p"t cent a year rate' starting Aä ph.li. ptàa"Ë,íon will also increase f he production' it mav il;;ouap* of 30 in 1962' For a high estimate on tP-h.D. procluction.will rate i further be assumed th"t th;';;r""t g:rowth 1SOS-1SZS Since it is difficult to iä*"i" ""¿""ged in the tetþ' p"t"iod can be sustaineil over a long maintain that such u pft""o-áouily high rate on some assumption as ;;i;ã, ; t""t" conser-vatíve ostimate rÀust be baseclFor the low estimate' a e i" ift"'ait"i"g of a tapering fi of the growth rate' t"i tfte ûrst year' decreasing uniformly 19 per cent $owth rate ¡ """"ft tU" Z per cent lóng-term growth rate char- tt"t*ã by 1.2 per cent per year to t ten-year period' **õiah; i aì" nf..i"¡ *ià""át i" genåral by the enil oI theSociety on Janu- "ä".tråã " r,36^0 itmbets ãf the Ãmerican'Astronomical hold doctorates or professorships' "-, I laR4 620 have U. S' "iådt"1t"t santl fringe asrronomers and persons "a"a"s ome ü,J'",,mI)-J;"d""u*a( 35 i I á-... Copyright © National Academy of Sciences. All rights reserved.

IN THE PREDICTED ASTRONOMICAL MANPOWER TABLE 2 UNITED STATES uNrFoRM cRowrr¡ RÀTE (79% a gea¡ or 4-gear d,oubling perlod) 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 43 59 71 83 98 118 I38 162 50 I95 Neø Ph.D.'s 663 703 751 8-tr 882 967 7071 7193 1337 1512 SubJotal . 11 14 16 18 20 10 11 12 13 l-54 23 Loss 653 692 740 799 869 953 1055 1175 1317 1489 Total 620 ø geaî ín first geaL d,eøeasíng to 7% ø geøÌ at eñd) cRowûr R.41æ (791¿ TÀPERED 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 42 49 56 72 8_t 90 98 106 113 64 Neu: Ph.D,'s 662 701 747 800 860 928 7004 1087 717',/ 7272 Sub-totøI 10 10 77 13 14 15 16 18 19 t2 1,5% Loss 652 691 736 788 847 914 989 1071 1159 1253 t: Total 620 ,il with primary interests in other ûelds, but there is probably approximate compensatíon by the active astronomers in the other 54 per cent of the mem- ,,1 bership who do not hold doctorates or professorships. The National Register ,i 'j. of Scientific and Technical Pe¡sonnel lists 483 full-time astronomers in the ii United States in 1962. (W. L. Koltun of the National Science Foundation, ,tl,ì il :t,l which maintains tle Register, estimates that tÏe listing, basecl on responses ii to a questionnairg is only 80 per cent complete. If allowance is made for ) l incompleteness and for about 40 Ph.D.'s added since 1962, and also for the standard loss of 1.5 per cent a year by death or retirement, found by the l ll National Science Foundation to apply generaþ ín scientiffc-manpower srü- veys, the corrected total becomes 626 full-time astronomers at the beginning :, of 1964. This is a confirrnation of the previous ffgure of 620, and that number i may be adopted as a base for the prolection. l Two projections are worked out in Table 2 and plotted in Figure 19. l|1 The high estimate shows an increase in total ashonomical manpower by a l l' ; / lactor o12.4in ten years. The low estimate proiects an increase by a factor of 2.0. Thís tabulation does not attempt to classify astronomers by categoties ì,,' of inte¡est-theoretical or observational, optical or radio, ground-based or ili space-oriented. Since shifts in emphasis occur quite slowly, no complete :' lrl overturn ín percentages would be expecteil in a decade. A prediction would I l ,i be hazardous, but the proportion of tlle student population in graduate de- i tLl partments that place emphasis on ground-based astronomy, compared with I .; ')' 36 l: Copyright © National Academy of Sciences. All rights reserved.

ì the proportion in departments that have taken up space-orienteil astronomy, *orild årgo" againsf any immediate drift away from the present division of interest. Conclusían The surge of students into the graduate departments of astronomy has fol- no sign lowed aiteaily upward course for at least six years, and as yet shows from the cur-rent enrollment are àf ,ou.rding oif. If only the Ph.D.'s expecteil in the countetl, a"sharp increase in growth rate of the number of ast¡onomers in the count yis ioevitable. Arry reasonable assumptíon about a ¡ounding-ofi *o*tí t"t* of graduate enrollment leads to not less than a iloubling of the iumber of astrolnomers in the United States in the next ilecade' --' iin"" grounil-baseil astronomy has been shown Jo be uncler-instru- program of new facilities that menæd forïe demand already ""ittittg, " to work efiectively at moilern *ilt p"t-it roughly twice ", -åoy obseivets i"lããop", *orrãt úe consiclered rash. There will sureþ be more than enough astronomers waiting to use the new instruments' Copyright © National Academy of Sciences. All rights reserved.

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Astronomy has as its domain the study of the celestial bodies—the sun, planets, stars, clouds of gas between the stars, galaxies—and undeniably the entire universe considered as a single system. Astronomy's goal is to learn the nature of these diverse objects and to relate their properties, their motions, and their distribution in space in a unified world picture; to understand the evolutionary development of the universe from the time of its formation to the present epoch of observation and beyond; and indeed to discover, if possible, its original state and its final destiny.

Emphasizing astronomy as a pure science, this report presents the challenges scientists and the government face in regards to radio and optical astronomical programs. Ground-based Astronomy: A Ten-Year Program explores a balanced course for new facilities of ground-based astronomy in the next decade, and provides recommendations to create a progressive program that considers a wide spectrum of past inadequacies and future growth components. Outlining guiding principles and estimates of facility costs, Ground-based Astronomy examines present positions in research and development to further advancement of astronomy in various sectors.

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