PHOTOGRAPHING THE SOLAR ECLIPSE

because we cannot see inside the Sun information about solar phenomena often must be obtained by studying events which occur outside the Sun but which are directly influenced by it for example the solar corona are constantly changing pearly white halo which envelops the Sun and extends in more or less definite rays or streamers since the corona is but one millionth is bright at the Sun it becomes fully visible only during a solar eclipse when the sun's disk is blocked by the moon the exact nature of the corona is not known but it's constantly moving patterns reflect the sun's changing magnetic fields and violent activities also the corona emits radiations which produce the aurora borealis and periodically interfere with radio transmissions on the earth coronal illumination is believed to be sunlight scattered by free electrons in the region close to the Sun and by interplanetary dust in the more distant areas some of our most interesting and least understood knowledge about the corona has been obtained by studying the spectrum of this scattered illumination the inner corona shows a continuous spectrum of sunlight while the outer corona reveals an absorption spectrum the dark lines being caused by elements present on the sun's visible surface since each atom or molecule absorbs a certain wavelength the elements can be identified from the positions of their absorption bands in the spectrum the lines are present in the inner corona as well but are obscured by the intense background illumination the coronal spectrum also contains a series of bright emission lines which are radiations emitted by highly charged ions of various atoms these ions can exist only when energy levels are high enough to alter the normal atomic structure for example the normal atom of iron identified as iron one has 26 electrons orbiting around its nucleus if the energy level increases an electron is displaced and the atom becomes an ion identified as iron - if the energy increases further and a second electron displaced the atom becomes iron 3 and so forth these displaced electrons move freely in the space around the Sun and help to scatter the solar radiation we see as the corona for each state of ionization an atom will emit radiations at characteristic wavelengths in the spectrum for example iron 14 which has 13 electrons displaced produces a bright emission line at a wavelength of 5303 angstrom units since the energy required to produce an ion is known we can determine the temperature where it exists ions reveal the temperatures of 1 million degrees Kelvin and higher occur in the corona while the surface of the Sun is only about six thousand degrees no full explanation has been found for this seeming incongruity however it would seem the coronal heating is mechanical in nature and probably resolves from pulses or shockwaves of energy travelling from the surface of the Sun the atomic particles in the corona become ionized because of the mechanical energy imparted to them by these shockwaves research into the mysteries of the Sun is continuous but it reaches periods of peak activity during each solar eclipse when the full corona can be observed and studied in recent years the Los Alamos scientific laboratory in New Mexico has become active in solar eclipse studies although Los Alamos is best known as a nuclear research laboratory and the birthplace of the Atomic Age the techniques employed in nuclear development work can be equally useful in solar studies for example the basic mission of these NC 135 aircraft is to provide stable high-altitude platforms from which precise measurements and observations can be made during nuclear research programs since the same qualities are desirable during solar observations the aircraft are well suited for this work as well solar eclipse expeditions undertaken by Los Alamos in May 1965 and again in late 1966 our typical of the laboratories research into solar phenomena preparations begin many months in advance for the three experiments Los Alamos scientists will conduct during the 1966 solar eclipse the specialized and complex instruments to be used are designed and built at the laboratory the largest is fondly referred to as the Rube Goldberg partly no doubt because of its obvious complexity basically the Rube Goldberg is an 80 inch focal length telescope to which are mounted several instruments for measuring and analyzing coronal light near the lower end of the telescope the main light path is divided by a mirror which reflects one-half the coronal image to a photographic interferometer the remaining part of the image is focused on to the ends of 36 fiber optic bundles which lead to a photometer and a photoelectric interferometer the bundles of glass fibers act as flexible light pipes which transmit light focused on them at the focal plane of the telescope the fiber ends are arranged in a radial pattern so that each bundle samples light from a different point within the corona illumination from the light pipes is analyzed to determine different types of information 30 of the pipes go to the photometer which measures the intensity of the light this instrument is a joint effort of the Los Alamos and Sandia laboratories light from the fiber-optic bundle passes through a collimating lens and a filter which blocks all wavelengths except those emitted by the bright emission of a certain high on the intensity of the light is then measured by a photomultiplier tube or electric eye whose output is recorded on magnetic tape the disks holding the light pipes and the filters can be rotated independently thus by sampling light from different fiber-optic bundles and by changing filters the intensity of various emission lines can be measured at many positions within the corona the photometer will measure the bright emission line intensity of iron 14 calcium 15 and iron 10 shown graphically the vertical scale represents the intensity of the spectrum and the horizontal scale its wavelength in angstrom units the gradually descending line is the background illumination in the corona while the bright eye on emissions appear as Peaks the filter in the photometer blocks the spectral light except at frequencies around the particular emission line being studied the output of the photomultiplier tube then indicates the relative intensity of this emission line the intensity of the other bright lines is measured simply by changing filters so that a different band of frequencies becomes visible intensity is also measured in the continuum regions adjacent to the lines in order to correct the measured emission line intensities for the background light the six remaining fiber-optic light pipes leading from the focal plane of the rube goldberg Kari coronal illumination to the photoelectric interferometer this instrument is similar to the photometer except that it determines the shape of the emission line rather than its intensity again light from the bundle passes through a collimating lens and a filter but then it must pass through an interferometer before reaching the photomultiplier the interferometer further narrows the wavelengths being measured by passing only a very small band of the light it receives it can be adjusted to vary the frequency of light passes the photoelectric interferometer will determine the shape of iron 14 and iron 10 emission lines as before the color filter serves to block all wavelengths except a relatively narrow band around the emission line the interferometer then narrows the band of transmitted light even further since the particular band passed by the interferometer is variable intensity can be measured at different discrete frequencies within the bright emission line a plot of these intensity levels describes the shape of the emission line which is important since the shape reflects the motions of the individual ions in the corona and therefore the temperature Rhona is viewed rather than just selected points and the images recorded into the diagnostic instruments that have been described the rube goldberg is also equipped with a 16 millimeter motion picture camera which monitors operation of the system and a photo tracker which keeps the telescope accurately aimed these units view the corona by means of a beam splitting mirror which reflects 10 percent of the light from the main optical path the data gathered by the rube goldberg will tell scientists more about the temperature of the corona and about the abundance of certain elements that comprise it another of the special Eclipse instruments is the coronal camera here the shutter is being checked to measure the precise amount of light transmitted at various operating speeds the camera uses a 36 inch focal length lens to photograph the corona out to a distance of at least five solar radii from the surface of the Sun exposures are made through a broadband orange filter in three planes of polarization the photographs resulting from this experiment will enable scientists to learn more about the electron density of the corona and about the structure of coronal streamers the third special instrument is the emission line camera which is equipped with nine separate 13 inch focal length eight of these focus images of the corona on a single piece of film while the ninth supplies an image to a stabilization and tracking system the eight lenses used for photography are equipped with narrow band filters each of which passes only the wavelengths of a particular ion or region of the solar spectrum the camera will record the emission lines of nickel 13 iron 14 calcium 15 iron 10 nickel 15 and three regions of the continuous spectrum near these lines the images will provide a photographic map of the intensity and distribution of these ions from which scientists hope to determine the varying temperatures throughout the corona the photo tracker for the emission line camera is the same as those used on the Rube Goldberg and the coronal camera an image of the object being studied in this case the Sun is focused on a ground glass plate where it can be observed by the operator within the plate are embedded four pairs of fiber-optic bundles which carry the illumination focused on them two light sensing photomultipliers the photo tracker detects errors in the position of the image as small as 10 seconds of Arc and send signals to the stabilization system to keep the instrument precisely aimed at the corona the normally spacious interior of the NC 135 research aircraft is nearly filled by the equipment that will be carried during the solar eclipse expedition starting at the forward section of the cabin the aircraft carries the coronal camera and the command and timing stations from which the mission will be coordinated next our electronic data recording stations and two large DRC cosmic ray detectors installed by the Lorentz radiation laboratory immediately after the emission line camera a gamma ray detector and more data recording and control stations the tail section houses the rube goldberg and additional cosmic ray measuring equipment including a unit installed by the Douglas Aircraft Company the Stinger like appendage on the tail holds a magnetometer for measuring the Earth's magnetic fields an important consideration in the design of the coronal camera seen here and the other instruments was that even while being carried in a moving airplane and subject to a variety of unpredictable movements they will have to track the image of the corona in space with great accuracy to satisfy this rather challenging requirement each instrument is equipped with three hydraulically operated aiming and stabilizing systems the first is a manual system which is used to aim the instrument with enough accuracy so that the automatic stabilizing units can take control a 3-axis gyro system similar to an autopilot then takes over and corrects the position of the instrument as necessary to compensate for movements of the aircraft the final system is the photo tracker which has been described the stabilization system is accurate enough that exposures as long as 30 seconds can be made without noticeable degradation of image quality since solar eclipses occur at irregular intervals and can be observed only from very limited areas on the Earth's surface scientists often must travel great distances to observe them the 1966 eclipse will occur on November 12th and his path of totality will move across the Atlantic Ocean off the coast of South America on November 3rd 1966 Air Force 369 the aircraft instrumented by los alamos leaves its home station at Kirtland Air Force in Mexico for the long flight to Buenos Aires Argentina [Music] to similar aircraft instrumented by the Sandia laboratory of a Lorentz radiation laboratory are also participating in the equipped study in addition both the National Aeronautics and Space Administration and the Air Force Cambridge Laboratory are flying aircraft on this eclipse since the long journey to Argentina and back covers a wide range of latitudes both north and south of the Equator the flights provide an excellent opportunity for measuring cosmic ray intensity and magnetic fields at high altitude over a broad range of the Earth's surface since it can fly well over 30,000 feet above sea level the MC 135 provides an ideal vantage point for studying solar phenomena at this altitude observers are well above most of the distorting mechanisms such as haze dust and clouds which occur in the Earth's atmosphere another obvious advantage of such an airborne observatory is that it can readily go to the site of the phenomena to be observed on November 5th the NC 135 s arrived at Buenos Aires where the nuclear scientists joined several hundred researchers from the United States and other countries who have journeyed to South America to study the Eclipse several other Los Alamos scientists have arrived at Rio Grande Brazil some four hundred miles east of Buenos Aires where they prepared to conduct another solar eclipse research project in this experiment instrument packages designed to measure x-ray emissions from the Sun's corona will be rocketed 250 kilometers above the Earth's surface each of the instrumentation units contains eight crystal spectrometers to measure x-rays emitted by highly ionized carbon nitrogen and oxygen atoms the packages are equipped with some sensing units which keep them correctly oriented with the Sun during flight three identical units will be launched at different times so that comparative measurements can be made of radiations from the clear Sun and during the partial and full phases of the Eclipse the data obtained by the instruments will be relayed back to the ground by means of a radio telemetry data link Los Alamos scientists work jointly with personnel from the Sandia laboratory who are responsible for the Nike tomahawk Rockets which carry the instruments the five days following their arrival in Argentina are busy ones for the airborne Los Alamos personnel and their Air Force crews [Applause] the scientists and long hours on the ground and during practice flights adjusting and calibrating their sensitive equipment the long practice flights allow the scientists and Air Force flight crews to check out the procedures and navigation plan that will be followed during the Eclipse flight the mission plan calls for the NC 135 to establish an elliptical holding pattern off the South American coast at an altitude of 32,000 500 feet at a predetermined time the aircraft will leave the holding pattern and follow a track that will precisely correspond with the path of the Eclipse the shadow of totality moving eastward approximately three times the speed of the NC 135 will catch up with cover and then move ahead of the aircraft since the airborne observers are moving with the shadow they will see the full Eclipse for about three minutes while observers on the ground will see it for only two minutes during all practice flights and the Eclipse mission the Los Alamos aircraft carries three Argentine scientists who conduct their own cosmic ray experiment by providing this service the Americans are able in a small way at least to show their appreciation for the excellent support and cooperation they are receiving from the Argentine government finally after the months of preparation and practice it is November 12th 1966 the day of the Eclipse Air Force 371 the aircraft instrumented by the Lorentz radiation laboratory leaves bueno Sade shortly after dawn to scout weather conditions along the proposed flight path the remaining crews and aircraft stand by until their scheduled times for takeoff if visibility is poor in the planned area the three aircraft will fly an alternate course to find improved conditions for viewing the Eclipse by the time the Air Force and scientific crews have boarded their aircraft word has been received from the airborne Livermore plane that weather conditions and visibility are excellent in the Eclipse area a short time later all three flying observatories circle in the holding pattern from which they will set out to chase the Sun shadow all right now I'm telling my car turn in there okay if we could I'd like to decent to get ground speed I think that there may be something about that serious going on Oh or it looks awful clear out ahead now as the aircraft fly in the holding pattern scientists make final preparations to ready their equipment for its brief look at the corona the magnetic tape units which record data from all the cosmic ray and coronal instruments are installed and duplicate to ensure that information will be obtained even if part of the recording equipment should fail each half of the double system records 50 channels of information okay we're coming up on a heading for the Eclipse for us ahead a healthy 137 the scientific commander observes the progress of the Eclipse and checks the position of the Sun in relation to the aircraft by means of an ingeniously simple Sun compass which uses a fixed lens to focus the sun's image on a chart approach of the total eclipse is heralded by the eerie half light of the gathering midday dusk as the moon gradually moves between the Sun and the observers that image is bright enough just to keep it off the fibers a little while okay oh sorry gonna cut the high voltage no you're all right I got the limp recovers in the right lift covered okay pictures will be started at 16 10 16 10 ok repose the ante and put in the 1.5 aperture okay we're set okay I'll pull it off it's exactly zero on Tom I can see the Kuroda on the other side of the Sun and I'll put it on to the fibers oh and trying to photo track better track into hell I can go to track @p you cannot wear you can tie 10-30 all right I've been head of track on two axes thoughts drifting away first all right PL exits better socket see actually Shiro that's the way it should be there's no light to the exes yeah 20 seconds filter for all right don't start going here come along you go ahead lose got it okay you completed that yeah don't forget your ramp when it's time alright 28 okay the provenances the toys-r-us let's filter to build up to green for all the light aha Venus Venus is approximately fired by the 10th degrees no five degree nice filter one robbing position filtered up a three three and nine twenty eight fifty two point eight two eight excellent tracking build an upper one one in still good Trekkie 20 seconds filters three Green to one of those Providence's is just at 45 degrees and it will hit the Pipers nicely 3 3 20 seconds filter 2 I'm saying two axes solitaire stop you are reversed and I'm pulling the polarizer polarizer it's pulled your first Matt go ahead start it in seconds filter three all right we're going unstable I've gone into gyro track all right your pastor contact boy passed a third contact awfully some out of the fibers what was the time of totality it was just about three minutes for life after approximately three minutes of totality the full Eclipse ends as suddenly as it began with the most critical part of the mission completed the crew members relax momentarily as the NC 135 begins its return flight to Buenos Aires however before the aircraft returns to the United States it will fly several more cosmic rays study missions that will carry the scientists far to the south almost to the Antarctic continent the photographic films and magnetic tapes recorded during the Eclipse are removed from the aircraft for careful storage until they can be carried back to Los Alamos to be processed and studied the solar eclipse expedition produced an abundance of raw data about the solar corona and hence about the nature of the Sun itself the films exposed by the emission line camera show graphically the distribution and intensity of various ion forms within the corona the coronal camera recorded more than 40 images at various exposure times in the longer exposures the coronal rays and streamers are visible out to a distance of about 6 solar radii from the surface of the Sun full interpretation of these photographic records and the electronic data from the rube goldberg recorded on magnetic tape will require many months of detailed study and analysis the knowledge thus obtained will help man to better understand the secrets of the Sun and the influence of solar phenomena in space and on the earth in large part the skills and equipment used by the Los Alamos scientists during the Eclipse expedition were originally developed for highly specialized nuclear research for example the sophisticated optical and electronic data recording systems are closely related to the diagnostic equipment employed during the testing of nuclear weapons and the NC 135 aircraft which proved so useful as flying observatories have as their primary mission an important role in the atomic energy development programs of the United States [Music] participation in programs such as the solar eclipse expedition provides an opportunity for Los Alamos scientists to maintain and increase proficiency in their specialized skills and at the same time permits the techniques of a unique scientific discipline to be used to increase man's general knowledge about his environment [Music]