a scieI1tist aI1d his hobby REFLECTIONS

On a cold, late evening last] anuary, of his origin, nature, and destiny; the disciplines of physics and mathe­ I called to my younger son to come in that presents to the eye only events matics, and this led to a career as a from his "observatory" in the front that are already past, yet with such physicist. To this day, continued yard. His reply-that it was neither precision and conviction that on its efforts to keep abreast of some of the too cold nor too late, and that school word I was one day to travel halfway major developments in astronomy tomorrow was much less important around the world for a date with sun, serve a double purpose, since many than] upiter's moons in transit now­ moon, and a bench mark. Which is by recent advances in physics are in­ set me to thinking. Time had now way of saying that by suitable choice volved. closed its full circle since his grand­ within the full scope of such a hobby, father, too, had turned resignedly from all ranges of ages, skills, and interests My limited purse, on the other a son whose inner clock ran on tele­ can find expression - from occasional hand, led inevitably to the attempt to scope time. diversion up to several lifetimes of build or improvise instruments. And serious activity. there are few who, having done so, I could not help but muse awhile will not put their efforts to practical on the propertks of this optic tube Suppose one takes a hobby point use. Whether simple star gazing or that bends light just so; that shows so of view perhaps best described as op­ attempting to photograph an astral clearly what young and old scarcely portunist, a sort of balance of one's body, holding "telescope night" for a can believe to exist; that, itself a purely resources of age, interest, and skill. In scout troop or taking off on an eclipse physical tool, enlarges man's concepts my own case, I chose early to combine expedition, a substantial reward library resources with an attempt to accrues. Each success carries with it a Irvin H. Schroader, Assistant Supervisor of develop manual skills. My early at­ sense of personal achievement; the the Satellite Design Group, is a member of tempts to read widely in the locally inevitable imperfections only whet the American Physical Society and of the American Association for the Advancement available literature on astronomy the appetite for another try, better of Science. soon required supporting study into planned next time if time allows.

Eclipse of the moon, September 25-26, 1950. The four views were selected from a series taken as the moon moved through the earth's shadow .. They were photographed by mounting a 3 5-mm camera, with lens removed, at the prime focus of a reflecting, 112-inch-focal-Iength telescope; that is, so that the telescope focused a sharp image directly on the film. The exposure was determined experimentally by considering the moon to be a cbunk of grayish rock illuminated by the sun.

8 APL Technical Digest of a TELESCOPE MAKER

I. H. Schroader

Grinding the Telescope 'Iirrol' carborundum grains between. The Russell Porter and Albert Ingalls, and upper disk, when stroked back and principally to the sponsorship of To illustrate, I recall standing in­ forth over the lower, tends to wear to Scientific American magazine. side the darkened dome that shelters a smooth concave surface if moved in the IOO-inch telescope on M t. Wilson, all possible directions. The rough Perfecting the ~lirror surface resulting is then made The working of glass is still largely smoother by several hours of grinding empirical- more art than science in with successively finer grades of abra­ its dependence on personal skill. The sive. mounting of the optics to form a com­ At this point, further progress to­ pleted telescope can be kept very ward a smoother surface requires simple unless the amateur decides to polishing by rubbing the upper con­ take a turn at fine machine work. One cave disk over a rouge-saturated layer of my own particular interests has of pitch. Some hours later, the surface been in perfecting the paraboloidal of the glass will become beautifully surface on a mirror and measuring it smooth and free of pits and scratches with high accuracy. This is a project if cleanliness is carefully observed. that consumes large amounts of time So far, work; from here on the em­ and little money-a good combination phasis is on minimum work with for a hobby. Section of the moon at first quarter, taken maximum skill, for the contour of the Surprisingly enough, the mirror by the same technique as that used in the September 25-26, 1950, moon·eclipse se­ surface of the glass must be carefully surface can be measured for deviation ries. The shadows cast by mountain ranges and crater walls cause the surface features modified so that it assumes the form from the desired paraboloid within, to stand out in bold relief. The mountain of a paraboloid of revolution (a dis­ say, 2 millionths of an inch by illumi­ range is the Lunar Apennines, and the larg­ est crater is named for Archimedes. torted pattern of stroking the upper nating it with an artificial star-an disk over its pitch lap is employed, so illuminated pinhole of light aimed to wishing for a look through the giant that more glass is polished away in strike the average center of curvature instrument. However, since the staff the center area of the disk). For the of the mirror surface. The mirror will astronomers themselves seldom ob­ tyro, give or take 5 millionths of an served visually, luck was not with me. inch is near enough to perfection. The With better fortune sometime later, final step requires that an extremely two nights spent at Lick Observatory thin layer of aluminum be evaporated provided opportunity for magnificent over the glass surface to render it observations of Mars, Jupiter, and highly reflective. When assembled in a Saturn that might have ended all tube, the curved mirror surface will satisfaction with smaller instruments then reflect light rays from a star to had not the element of personal form a real image that can be further achievement counted so heavily. enlarged by a magnifying eyepiece. So I made a telescope of my own by The first look through one's own the following process, based mainly on creation is a never-to-be-forgotten simple principles and hard work. Take experience. Thousands of amateurs two round disks of Pyrex glass,' say 6 of all ages have completed successful Comet Ar.end-Roland, taken with a 35-mm inches in diameter by I inch thick, and instruments, thanks in large measure camera attached to a 6-inch telescope. The telescope was mounted so that it could be grind them together with coarse to the guidance of such men as the late moved to follow the motion of the comet.

July - August 1963 9 retlect the incident light back to a somewhat distorted image of the pin­ hole. So simple a device as a razor blade can then be used (by slicing the light, so to speak) to locate the point where rays of light from any small selected area on the mirror come to a focus. Eye and mind can soon be educated to "see" the contour of the glass surface, with deviations from a perfect spheroid as small as a fraction of a millionth of an inch standing out in bold relief under test. A combina­ tion of measurement and simple calcu­ lation leads to a knowledge of the actual mirror surface contour, which Illustration of the Foucault test setup for determining precision of mirrors during polishing. can then be corrected toward perfec­ tion by always polishing off the high when compared with precise meas­ cause of some minor imperfection in places. This method of testing bears uring screws. Second, the test instru­ the equipment. ments and methods have been used the name of its inventor, Leon ) lot()graph~ and AstronOlll. Foucault.! repeatedly, with a high degree of By a combination of the mathe­ success, by a number of interested To be continually attractive, a matics that describes in detail how a telescope makers. Third, I completed hobby must offer less demanding goals 2 paraboloid reflects light and an in­ a chapter in Amateur Telescope M aking as well. With little talent for sketching, genious use of fine wire for examining describing the test in detail. I have had only limited success in the reflected image of an illuminated A major undertaking in mirror drawing what is seen through the slit, Enrique Gaviola devised a making is the task of working a disk of eyepiece. On the other hand, photo­ " caustic test" for determining mirror glass to achieve a surface contour so graphing astronomical events and ob­ accuracy. This method depends, for close to that of a perfect paraboloid jects has proved to have very interest­ its high degree of accuracy, upon the that testing errors become important ing possibilities. I have tried a variety uniform diffraction of light around a in stating the accuracy achieved. It is of devices, from very simple lenses up fine wire. The position of the wire evident that glass can only be removed, to those in much more sophisticated must be known accurately as observa­ so the worker must continually think cameras. Perhaps most interesting tions are made to measure surface in­ in terms of an imaginary surface lying have been attempts to photograph the accuracies as small as Hoo of the principally just under the actual glass moon, planets, and comets, using the wavelength of light (about .>-5 of a surface. As the real and imaginary greater light-gathering capability and millionth of an inch). surfaces approach each other within resolution of the largest available tele­ Over a period of several years, less than a millionth of an inch, the scope. Here again it is easy to become worked with the late A. G. Ingalls, a work of wearing away the high areas absorbed in an attempt to develop Scientific American staff editor, on ways must approach the vanishing point, techniques to the limit of perfection of developing this technique so that it perhaps 7100 of a millionth of an inch and then play games with atmospheric could be used by amateurs. Of particu­ of glass removed per stroke. At this turbulence in the hope of catching the lar interest, the instrument for moving stage the emotional outlook of art, the sharpest possible images. the wire with a precision of, say, 200 rational viewpoint of science, and the Whatever the success achieved, it is millionths of an inch had to be de­ empirical basis of technology blend in an established fact that the eye and signed with the limited shop facilities almost exquisite form to force comple­ mind can better read through the of even the advanced amateur in tion before the anguish becomes un­ atmospheric turbulence to catch and mind. In simple terms, a form of con­ bearable. I have succeeded on surfaces remember fine detail momentarily struction that depended on the assem­ as large as 12 inches in diameter, less perceived than can the photographic bly of readily available materials well on larger surfaces. In defense of image that averages its impression had to be used. Careful adherence to such painstaking effort, it must be over the exposure interval. An ama­ the principles of geometric design realized that the constant turmoil of teur's carefully made 12-inch tele­ virtually assures required accuracy. the earth's atmosphere will often blur scope directed at the moon or planets This effort brought success of several the finer details of even the most will show to the eye all that can be kinds. First, several test instruments marvelous image- of Mars, for ex­ photographed through the largest were constructed and tested, using ample. However, the chance-of-a-life­ telescopes with present cameras . only hand tools and inexpensive, com­ time critical moment on an almost mercially available components; these perfect night can be lost forever be- A Family ,\ffair proved to have the required accuracy There are times when nature con­ 21. H. Schroader, "The Caustic Test," in trives to schedule an event so fleeting 1 A. G. Ingalls (ed.l, Amateur Telescope M.ak­ A mateur Telescope M.aking (Book Three) ing, Scientific American Publishing Co. A. G. Ingalls, ed., Kingsport Press, Inc. or so magnificent that photographic New York. 1933. Kingsport, Tenn., 1953. coverage with the best equipment on

10 APL Technical Digest command at the time becomes an by gasoline-lantern light. By then the To t le Fa C r "'r." ~f the P urgent necessity. Thus, an entirely new day's thunderstorms went their way Some months later, at lunch with area of interest opened up for me and left the atmosphere crystal clear Father Heyden, S.j", Director of several years ago. for a never-to-be-forgotten 60 seconds Georgetown University Observatory, A total eclipse of the sun always of totality. when he mentioned his need for help occurs somewhere else, and it almost By careful pre-planning, I managed at a forthcoming eclipse, I literally demands a photograph to convince to squeeze into that interval six ex­ leaped up to volunteer at a chance to one of its reality since it is here and cellent exposures on Kodachrome film, go on a real eclipse expedItion. This gone in seconds. Contrary to the im­ ranging from >~ o second up to 15 one had elements of travel, diplomacy, pression so far given, amateur seconds in duration, along with a quick science, and adventure, along with a astronomy is not necessarily a lone­ look at the sun. The first exposure re­ chance to make a useful contribution wolf operation. Early in 1954 I ex­ corded the last thin crescent of the to geodesy. I was to be responsible for changed correspondence with Mr. L. sun's photosphere-an instant before a team of five men to photograph a A. Pommerening, Forest Supervisor of the moon completely blocked its not-quite-total eclipse of the sun from a Chequamegon National Forest in blinding radiance- to reveal the location in Ceylon. The carefully Wisconsin, asking for permission to set fainter crimson chromosphere ac­ timed observations were to be com­ cented with hydrogen-gas prominences up equipment to photograph the June bined with those of other groups that exceeded five earth diameters in 30 sunrise eclipse of that year. The spread out along the eclipse path in forest would provide a pleasant camp­ height. Stepwise increases in exposure Africa and Asia in an attempt to inter­ enabled the limited dynamic range of ing vacation as well, but posed the lock geodetic survey grids and perhaps difficulty of finding a clear shot at Kodachrome to record, first, the to derive an improved radius of the sunrise. Mr. Pommerening kindly pro­ chromosphere, then the relatively earth. vided a clear location at the base of bright inner corona, with the longest A travel log filling a secretary's note­ Long Mile Fire Tower, which indeed exposure recording faint extensions of book twice over, hundreds of color proved perfect. the corona extending outward several slides, and some vivid memories re­ This kind of thing can become some­ sun diameters before fading to the main as mementos of the trip. Among thing of an adventure, with family, same brightness as the general sky them, from my notebook, is the sim­ dog, and equipment to care for, along illumination. Here again the eye ple entry: with mounting concern over losing proved vastly superior to film in reso­ everything to the weather at the ap­ lution and dynamic range. In the 20 "Saturday, November 26- Al Kobar: ' pointed moment. My telescope, seconds remaining after exposing film, mounting, and camera were cleaned, I was easily able to observe and re­ followed by five blank pages. And set up, and adjusted in fine June member, well beyond the camera's thereby hangs a tale of East meets weather, and in a cloud of flies that ability to record, both the magnifi­ West with but slight understanding of literally covered every square inch of cence of the phenomenon as a whole each other. exposed skin. It was impossible to kill and the ray-like structure of the corona The five of us from APL- C. T. them (two boxcar loads had just been with its faint extension. Holliday, L. W . Fraser, L. W. Bennett, imported to eat tent caterpillars), just Even the best laid plans can go D. C. Small, and I - went by cab from grin and bear it while my family astray, however. The inevitable small Dhahran Air Force Base, Saudia, complained from behind mosquito detail overlooked showed up as a neat Arabia, to visit the small nearby Arab netting. Seven hours before sunrise my crescent-shaped hole in the camera's town of Al Kobar. We were wary with German shepherd lost his challenge shutter, burned into the black cloth our cameras lest offense be taken by match with a porcupine; he was a as the sun waxed large again. For­ some devout Mohammedan who pitiful sight for some hours as I re­ tunately, my exposures had already might involuntarily become accessory moved quills and dressed his wounds been made. In another way, I came to the formation of an image, ex­ close to complete failure not more than pressly forbidden as they read the Ten a minute before the total phase be­ Commandments of Moses. Somehow gan. I had made no provision for we wandered too close to the resi­ shielding the telescope lens from the dential area and shortly were on our dew that inevitably forms as the tem­ way to the local police station under perature drops rapidly, leaving the armed escort (a bayonet). There we glass cooler than the moist air. I knew were courteously seated, facing the that wiping the moisture away would police captain in western military uni­ be utterly useless, as it would quickly form and several other personages in reform. What a welcome sight it was white robes. Their English vocabulary to watch the dew evaporate in the seemed to consist of the word "pic­ warmth provided by my Coleman ture," and later also of "women," at lantern, which, by great good fortune, which we then realized our predica­ The Solar Corona, June 30, 1954 (from a was still burning. Three hours later ment. My Arabic escaped me, and Kodachrome original). The original was made by attaching a 35-mm camera to a we left the site to the flies, gathering English protestations were in vain un­ small telescope, of 35-inch focallengrh, storm clouds, and a porcupine in a til Lorie Fraser, in an inspired that was mounted and clock-driven to follow the sun. tree. moment, took up a slow chant-

.lilly - August 1963 11 time indication with that broadcast throughout the world by WWV and log the difference within a few thou­ sandths of a second. The task facing us was to photo­ graph the sun well over 100 times during the eclipse, record accurately the instant in time when each ex­ posure was made, and get the photo­ graphic negatives safely returned to Georgetown Observatory. A number of technical details had to be worked out on site. Very slow (low-sensitivity) glass plates were to be used rather than the more familiar film. Each plate had to be loaded into "old­ fashioned" plate holders. This would have been easy in a darkroom with a safety light; in our case, however, the darkroom was a light-tight box about the size of an orange crate. Plate hold­ ers entered and left the box by a light­ tight sliding trap door, while the operator's arms worked through light-tight sleeves. With only four plate holders on hand, the trick was to keep up a rate of one exposure every 30 Eclipse day, Ratmylana Airport, Ceylon. Clyde Holliday (left) and the author are at their op­ seconds during the middle of the erating stations. The remainder of the APL group are at stations in the tent to the right, and a group of interested Ceylonese form the background. eclipse. Lorie Fraser's practiced hands made it with not a plate out of order. "American School Professor edge of the airport, a concrete pier Clyde Holliday struggled with de­ American School Professor . ... " had been poured to serve as a stable velopment of the test plates, first in the A few minutes later the local high base for our telescopic camera. An tropical heat of an improvised dark­ school teacher (English and algebra) insulated tent set up by the army of room in the hotel, but later in a cool arrived to solve the communications Ceylon proved its value twice over­ darkroom at the University of Ceylon, problem. Our penalty, as provided by as a shelter from the midday heat and through the kindness of Professor law : turn in our film for local develop­ from the frequent rains that charac­ Mylvanagam, head of the Physics ment (Kodachrome!) to verify the terize the transition period between Department. absence of feminine images, after one monsoon season and the next. Techniques of loading plate holders which it would be returned. The police There followed busy days of prepara­ at the telescope, guiding the telescope, chief made this verification on the tion; what hadn't been accomplished etc., were worked out to perfect the spot by pulling the film out of one in the States had to be finished now, routine. My experience with the spool. Just as I had said, no women. with masking tape and the like. burned shutter in 1954 emphasized An important task was to place in the ever-present possibility of a slip-up ~ 00 ng t c ~ se operation a precision crystal-oscillator due to inattention, momentary dis­ Three weeks before Christmas, 1955, clock and a radio receiver, and to pro­ traction, or even boredom with rou­ we were registered in comfortable vide a standby generator in case of tine. As a drill, we photographed the quarters at the Mt. Lavinia Hotel power failure. The clock had to be setting sun on several evenings and located near the capital city of kept running at all cost, for upon its developed the plates to assure our Colombo, Ceylon. Clyde Holliday accuracy depended a major factor in success. As we drilled, each man de­ and I shared a room overlooking a the success of the expedition. Each veloped the habit of "talking out" fine beach. A few miles away, on the day it was necessary to compare its each step of his chosen task, and listen-

n• • • • • • • • Partial eclipse of the sun, from a series photographed in Ceylon.

12 APL Technical Digest ing at the same time, alert to act as philosophy that must be accommo­ prompter if anyone should bypass a dated if a somewhat dependent econ­ single important step. omy is to survive. We came to December 14 a well­ It seemed not a little strange that as drilled team. I recall wondering how eclipse day neared, some degree of foolish we would look to the local apprehension developed throughout people gathered around if nothing the local population. They had lived should happen. Much to my relief, the through a total eclipse in the previous eclipse arrived on time and passed June, during which many of the people without incident; perhaps the local became genuinely fearful at the sun's Buddhist priest present in the group apparent demise, and were impelled around us served as a stabilizing factor. to restore its former vigor with ap­ We exposed 135 plates before the propriate ceremonies. temperature drop literally brought I was pleased to repay, in part, Pro­ down the curtain on the show clouds. fessor Mylvanagam's favor by writing After a few minutes of elation, the a letter to the University Dean on be­ The author in a moment of relaxation, homeward-bound phase began, and half of the Professor's assistant, Mr. P. at Kandy, Ceylon. it ended at home three shopping A. S. Perera. Mr. Perera had assisted servatory design study was made by a days before Christmas. It could have us with darkroom work at the Uni­ group of engineers and scientists at the been much later, considering the date, versity, made a modification to the Laboratory in cooperation with the for the transportation officer at plate-changing box that enabled us to NASA program for space astronomy. Dhahran tried to send us the long way change plates at a faster rate, and The conclusion of the study incorpo­ home to relieve pressure on his sector. assisted at the site on eclipse day. The rated a telescope design best described By the way, there was one technical letter, I understood, would assist Mr. by the accompanying illustration. failure I must confess- a shutter again. Perera in his application for an assist­ Basically, it is a large reflecting tele­ Half in jest I asked Clyde Holliday antship at Cambridge University. scope (up to four feet in diameter) to one day whether he had checked the be placed in orbit by state-of-the-art shutter of the movie camera he was ~ew Fields to Conquer rockets. Once in orbit, it would relay using. "No," he replied, "but it's the A few years later, and back on this observations back to the ground con­ only thing arou!)d here we haven't side of the world again, other intensely trol station by television and by telem­ checked!" The developed film proved interesting opportunities developed. eter. An important feature is the once again, to our sorrow, that every­ Two of these have absorbed a major system of reaction wheels, which thing must be checked. Every frame of amount of my time at the professional serve to move the telescope under seven rolls was ruined. level. These are the Orbiting As­ ground-based control signals for aim­ With the technical mission accom­ tronomical Observatory and the 60- ing the telescope and for precision­ plished, I cannot help but reminisce a foot-diameter radio telescope nearing tracking of an astronomical body bit about the personal impact of the completion at the APL Howard under study. trip. It was my first trip out of the County site. Another requirement of this age is country, save Canada. Over and over The Orbiting Astronomical Ob- that of transmitting to and receiv"ing again I could only think in terms of how I would feel if my family had to live in such a way as we saw around us MIRROR STABILIZATION in many places. Often only a few steps WHEE LS separated youngsters without hope from those surrounded with every evi­ dence of good living. Our senses eventually became saturated and numbed in the face of our utter in­ ability to do anything about it. Colombo is a beautiful city, with OPTICAL AXIS less that detracted from this beauty X than in many an American city. A one-day trip to Kandy, the ancient capital city of Ceylon, seemed to con­ firm our impression of a clean, well­ dressed, well-fed, and friendly people. Yet Ceylon in that December was in the midst of an election campaign, carrying with it many overtones of the SUN STAR SEE KER TRACKER problems a young nation faces as it develops in self-government-prob­ lems of race, language, and political The orbiting telescope designed at APL, showing major control components.

July - August 1963 13 signals from space. The Laboratory has invested in its future capability by installing a high-performance radio telescope, which consists of a 60-foot­ diameter reflecting paraboloid with associated support, and aiming and driving mechanisms. I shall soon finish my present responsibility as problem sponsor and will then turn to its use. One of the most intriguing possibilities is its use for radio astronomy, a new field of astron­ omy based on the radar technology developed during World War II.

If,

Much of this story was written while making preparations for eclipse day on Saturday, July 20, 1963, again at the request of Georgetown University. Our destination was Ellsworth, Maine. My first responsibility was to repeat the Ceylon experiment, namely, to photograph the partial phases of the eclipse. Three Georgetown astronomy The author is seen on site at Ellsworth, Maine, adjusting the Questar telescope in preparation students collaborated on this project. for photographing the total eclipse ofJuly 20, 1963. The resulting plates were to be meas­ ured in a digital data-reducing part of the event. For this purpose, a re-aimed and I made my first exposure machine at the observatory in order to Questar telescope and camera, on loan on the last thread of the photosphere, define accurately the moon's position from L. R. Sanford (APL), and the for a fine "diamond ring." Six more at mid-eclipse. same camera and lens that were used exposures were crowded into the Results from two other experiments in Wisconsin in 1954 were set up and allotted time, along with a quick look were to be compared, in an attempt checked out. through binoculars-and then it was to detect the errors that were char­ Friday dawned fair but ended over. Just as quickly, and almost as if acteristic of each. One of these cloudy, an ill omen. True to the planned, solid clouds ended all further experiments involved measuring the weather reports, Saturday was the observations. sun's waning and waxing light by same. Both tension and cloud cover I am often made curious by the means of a photometer, from which increased as groups sought shelter viewpoint of persons who look with mid-eclipse time could then be deter­ from the midday heat in order to wonder through my telescope, and mined. The other experiment was to smooth their working routines. Since then ask, "Doesn't it make you feel photograph the sun's spectrum on there were only 45 seconds of totality utterly insignificant?" True, we are movie film, starting a few seconds available, every second had to count. smaller than much of the universe before the total phase. For a brief and are possessed of less energy; but When first contact was announced, interval the resulting spectrum changes it is also true that we are larger than it was a thin black notch most notice­ suddenly from absorption to emission much of it and possessed of more en­ able on the five-inch-diameter image -the flash spectrum-just as the ergy. These factors, of course, count on the ground glass of Clyde Holliday's sun's disk is covered by the moon. heavily in brute contests of will. But camera. A few shots were made on My task being an old one, it went scientific man looks ever for new schedule, but then we began to expose without incident right into the knowledge, fer more effective ways to plates whenever breaks in the clouds eclipse itself. Meanwhile, I helped control, in man's behalf, the large permitted, for a total of 13. By 5: 30 Clyde Holliday and Lowell Bennett forces of nature. PM it was obvious that only pure luck adjust the Georgetown cameras that In such a contest, individual man they were to use to take black -and­ or a miracle would allow us a look at possessed of rational mind and skilled white and color pictures of the suo. the total phase. hands can well afford to lay aside the Since I was not needed to operate Our low spirits must have showed as arrogant pride associated with brute the Georgetown camera for some ten groups wandered from their stations, force in exchange for the ever-renew­ minutes before and after the total but with only seconds to spare a sudden ing personal satisfaction that comes phase, there would be time for pic­ shout directed all eyes to the thinnest with accomplishment of a useful re­ tures on my own of the most exciting ghost of a crescent sun. Cameras were sult.

14 APL Technical Digest