THE PHOTOGRAPH IN Figure 2 shows a part of the sun's visible disk, or photosphere, as it appeared on February 13, 1956. The clearly defined spots and sharp granules demonstrate how effectively the sun can be photographed in white light with a small telescope and an ordinary camera. The picture was made, partly for amusement and partly to show what can be accomplished with simple equipment, by J. H. Rush, a physicist of Boulder, Col., who insists that all science is essentially an amateur pursuit. "By that," he writes, "I mean that when science quits being fun and becomes just a way to make a living or a reputation, one is no longer a scientist."

By this standard Rush has been a scientist since he was 12. "One night I went out to draw a bucket of water from the cistern on the Texas farm where l grew up. I was facing north, and as I stood leaning back against the tug of the pulley rope with nothing much on my mind I recognized the Big Dipper. Stars I had always seen before as a random scatter suddenly fell into a beautiful pattern. Life was never the same again! Shortly thereafter I managed to find some nondescript lenses and fitted them into a caricature of a telescope. It wasn't much as telescopes go, but its power and my enthusiasm both approximated those of Galileo and his first instrument. Curiously I cannot remember my first look through a respectable telescope. It was years later and by that time I knew too much to be greatly impressed.

"But I still enjoy tackling problems in science with equipment normally available to amateurs. The sun is a particularly appealing object in this sense Its abundant light permits excellent photography without need for large telescopes or precision clock-drives. It also has the advantage of shining in the daytime! Amateurs have reported varying degrees of success in photographing sunspot details and the granulation of the photosphere in white light, but many have failed to recognize the full potential of this simple method and the possibility of employing it for-recording certain information about the sun which is greatly desired.

"The granular pattern of the photosphere presents some of the most puzzling questions in solar astronomy, and is the subject of increasingly intensive study. The idea is generally accepted that the photosphere is the outside of an opaque layer of gas through which energy is transported out of the interior of the sun by convection. On this theory bright granules are the tops of rising columns of very hot gas, and dark granules are cells of cooler gas descending back into the interior. Or maybe it is the other way round. In any case, the convection turbulence that appears as mottling or granulation of the photosphere in white light is believed to be intimately related to the spicules of the overlying chromosphere. These spikelike jets, which can be observed only at total eclipse or with coronagraph telescopes at high altitudes, seem to be projections to higher levels of the uprushing gas of the convection cells, which has become transparent, The spicules seem to represent a key process in the maintenance of the corona and in other phenomena of the sun's atmosphere.

"The subject is complex, but enough has been said to indicate that the granular pattern of the 'quiet' photosphere is at least is significant a clue to the sun's behavior as the more spectacular sunspot regions Moreover, granule cells are easily observed in the gray penumbrae of spots. In at least one instance they have been observed in the dark umbra itself. These and other observations of spot detail pose intriguing questions as to the relation between sunspots and the undisturbed photosphere, and the nature of the spots themselves.

"The most obvious approach to the study of the granulation is to determine the frequency distribution of granule sizes, and to find out whether this distribution varies in the vicinities of sunspots, or with solar latitude, or during the sunspot cycle. Several studies under very good seeing conditions have indicated that the granules vary in size over a wide range, the most frequent diameter being about 800 kilometers. These studies do not agree as closely as one would like, and theoretical reasoning—supported by some recent observations—suggests that granules much less than 800 kilometers in diameter must be still more numerous. Why are they not observed? Mainly because the earth's atmosphere is too unsteady. Instrumental defects and heating contribute to the difficulty. Few observers have claimed to find meaningful granular detail much below one second of arc, which is about 725 kilometers at the distance of the sun. Yet so important is this question to a better understanding of the processes going on in the sun that a project is now under way to mount a 12-inch telescope with a photoelectric sun-pointing mechanism on a balloon and photograph the granulation from an altitude of 80,000 feet [see "Science and the Citizen"; SCIENTIFIC AMERICAN, September].

"The problem of extending the observations to granules smaller than one second of arc is not for the amateur, unless he is an instrumental genius. But details of that size and larger often can be photographed, if one is patient and uses suitable techniques, and such observations may contribute toward an understanding of certain solar problems. Besides, the work is fun. Rather than generalize, I shall tell in some detail of an instrumental arrangement and technique that I have used with good results for photographing the granulation and sunspots.

"This work was clone in the late winter and spring of 1956 in the physics department at Texas Technological College. The school is located at Lubbock on a high, flat plain at an altitude of about 3,500 feet. The region probably would be excellent for general astronomical work, if it were not so arid and bare of permanent vegetation. The air usually contains a great deal of suspended dust and thermal turbulence is serious–particularly during the months when the ground is exposed. The visual seeing is usually good at sunrise. It deteriorates rapidly as the ground is heated, and by noon is usually so poor that it prohibits any worthwhile observing.

"Seeing is not a simple matter, however. I found during the period in which I made regular observations that the image of a sunspot usually looked as if it were under water ruffled by the wind. Despite the 'rubbery' appearance of the image the fine detail in it appeared to be good. Apparently a considerable area of image could be displaced at a visible rate, perhaps 10 oscillations per second, without much blurring or distortion of internal detail. Photographs confirmed this impression. A speed of even 1/125 second was enough to 'cut through' the slow, visible disturbances and yield good detail. A variety of evidence indicated that the long-period, large amplitude seeing disturbances that were disastrous to visual work originated very near the ground, while the type of bad seeing that blurred and distorted the fine photographic detail originated at high altitudes and was relatively independent of local conditions and the time of day. In this connection, it is interesting to note that W. A. Miller of the Radio Corporation of America Laboratories (to whom I am indebted for much of the 'know-how' of such observations) has obtained many excellent pictures of the solar granulation at Rocky Point, Long Island –but only when the sky was hazy! When the sky cleared, the seeing went to pieces.

"The best photographic seeing I found at Lubbock occurred about the end of January, 1950, when the sun came out after a week of heavy snow and cloudy weather. On that day the transient spectral colors (not halos) that are common at 10,000 feet in the Rockies appeared in light clouds near the sun, and the sky was the deep blue that is seen at the top of a mountain. Excellent conditions persisted long enough for me to obtain the photographs reproduced here of the great sunspot group that traversed the visible hemisphere of the sun from about February 10 to 23. The printed reproductions cannot, of course, do justice to the exquisite detail in the negatives, which in the best pictures was very near the theoretical resolving power of the five-inch objective that I used. The photographic seeing gradually deteriorated as the windy spring season came on and the clean air once more was burdened with suspended dust. By May opportunities for good photographs were rare.

"The equipment I used is illustrated in the accompanying drawing [above] The High Altitude Observatory of the University of Colorado lent us a portable refractor with an excellent five-inch objective of about 60 inches focal length. To this I fitted a large low-power eyepiece taken from an ordnance telescope, and a Speed Graphic camera with the lens-and-shutter assembly removed. To hold the camera in alignment with the telescope, I clamped a one-by-four-inch stick to the telescope tube and mounted the camera on the stick. After focusing and loading the camera I simply steadied the stick between my knees while leaning forward to check the position of the solar image on the focal-plane shutter screen, and fired the shutter. No motion blurring ever appeared. The mechanical details of this arrangement are unimportant; I mention them only to indicate that good results in work of this kind can be obtained without elegant design or precision workmanship.

"The logic of such an improvised setup is devious, as any experimenter knows. In this case it went somewhat as follows. I had a five-inch objective with an ideal resolving power of about one second of arc. Not wishing to sacrifice any of this resolving power by Stopping down the aperture to reduce the brightness of the image, and having no shutter speed greater than 1/1,000 second, I had to magnify the primary image sufficiently to hold the exposure time to something greater than 1/1,000 second on very slow emulsion. A large image makes visual focusing practicable and saves a lot of tedious photographic calibration–and also saves having to make a camera mount stable enough to hold such an adjustment from one observing period to the next.

"The physics department's Speed Graphic made negatives 2 1/4 by 3 1/4 inches. I settled on a solar image diameter of about three inches, mainly because that was the size that resulted from mounting the camera on a certain one of several holes I had bored in the stick. The adjacent holes corresponded to image sizes that departed too far from the exposure requirements. The plateholders were designed for cut film only, but I wanted to use some Eastman 549-GH glass plates I had cadged from High Altitude Observatory along with the telescope. I cut the plates small enough to fit inside the film slides and stuck them to pieces of cut film with pressure-sensitive adhesive cement (ordinary rubber cement or two-sided masking tape probably would work). One such plateholder with an undeveloped plate served as an excellent focusing screen. The usual ground glass was useless for this purpose; but the yellowish, fine matte surface of the emulsion yielded an image by reflection that was easily viewed and rich in detail. I found it possible to focus critically by eye, racking the eyepiece lens relative to the fixed objective and camera. However, a low-power reading telescope would have been helpful.

"No light-tight cover between telescope and camera was necessary. A large piece of cardboard fitted over the objective cell shaded the equipment from direct sunlight. Since the image was nearly three times as bright as full sunlight, the indirect light that reached the plate was insignificant. I racked the camera bellows back out of the way while focusing, and then extended it during exposure just for safety.

"Lest this account leave the impression that one can throw together anything handy and come up with good solar pictures, it may be worthwhile to point out the essential technical features of the arrangement. First, of course, is the objective. Besides being of excellent quality, it must be large enough to resolve significant small detail. The resolving power of a telescope is inversely proportional to the diameter of the objective aperture, and it is convenient to remember that–subject to some qualification– a five-inch objective can just resolve distinct details one second apart in the object. Even a two-inch instrument will reveal granular details in the photosphere; but these will lack the crisp quality and fineness of structure that can be obtained with a larger instrument at times of superlative seeing. A refractor has some advantages over a reflector, because of the superior optical corrections that are possible in a two-element lens and because of the tendency of a mirror to warp slightly in the heat of the sun. But although I have not tried a small reflector for solar work, I see no reason why a good mirror judiciously used should not give satisfactory granulation detail near the center of its field.

"For the finest work it is best to use a long telescope and photograph the primary image. The amateur, however, is usually limited to a telescope too short to produce an image large enough to avoid compromising resolution with the grain of the photographic emulsion. Furthermore, the f ratio for a short telescope of four or five inches aperture is so great that the necessary exposure time becomes impossibly short for any ordinary shutter. Filters can be used to reduce the light intensity, but they have serious drawbacks. A filter placed near the focus is exposed to intense heating, and any lack of uniformity in its density will show up with startling strength on the high-contrast emulsions that must be used for granular work. A filter near the objective is free from these disadvantages; but it must be as large as the objective, and of similarly high optical quality, or it will affect the definition. Consequently it is usually more practical to introduce a second lens to form a magnified image of reduced brightness, even though any such additional optical element necessarily causes some further deterioration in image quality. In a system designed for this work the second lens would bb carefully computed to match the objective and the conjugate distances at which it would be used. But the amateur usually does what I did at Lubbock. He picks up the most likely looking piece of glass that is handy and tries it to see what will happen. I was lucky.

"The ordinary camera leaf-shutter, working near the lens, is not satisfactory for solar photography. The exposure time is so short that the shutter has hardly opened before it starts to close. Thus if the shutter is used at the magnifying lens, the average aperture during the exposure is not circular and is substantially less than the full aperture of the optical system, so that the resolving power is reduced. If the shutter is operated at the primary image, various portions of the field receive different exposure times. The-only good way out of the dilemma is to use a moving-slit type of shutter (such as the shutter of a Graflex camera) at the primary image or just in front of the film. The latter location is preferable, of course, unless you are using a specially made shutter for the small aperture at the- primary image The main criterion of quality for a focal-plane shutter is uniform speed of travel. Sometimes such a shutter, particularly an old one, is unsatisfactory for high-contrast work because its progress across the image field is jerky and results in bands of varying density on the negative. This trouble may appear on high-contrast emulsions despite satisfactory shutter performance in ordinary pictorial work. I had no such trouble with the new Speed Graphic that I used.

"Given an adequate telescope with a good shutter, the remaining crucial requirement for white-light photography of the sun is a suitable photographic material. Ordinary films designed for pictorial photography have not nearly enough contrast, and usually too much grain, to render solar details satisfactorily. Kodalith or Reprolith can be used with some success, but even these high-contrast copying films are inadequate for solar granulation. Some amateurs have obtained good granulation negatives on Kodak Micro-File film; I have not tried this material.

"The best emulsions I know for solar work in white light are Eastman 548-GH and 549-GH. Of these the 549-GH yields somewhat more contrast and shows less stain; but either is capable of a gamma of 14 or better. These emulsions are very slow. The 548-GH has about a twentieth the speed of Eastman lantern-slide plates, and 549-GH is about three times slower. (Note that I exposed a three-inch solar image from a five-inch objective about 1/250 second on 549-GH!) Thus these materials eliminate the problem of shutter speed v. telescope aperture that makes the use of faster emulsions so difficult. Of course this problem is still serious if you use; an image much 'smaller than-three inches. The resolution of these slow emulsions is extremely high. The manufacturer states that 548GH will resolve more than 1,000 lines per millimeter, and 549-GH more than 1,500.

"The relative sensitivity of Type GH plates to various colors is important. Granulation photographs in the full white-light spectrum yield less detail than in more restricted regions, and some observers report more detail in yellow-green light than in the blue. The GH color sensitization extends the basic blue sensitivity of the emulsion far into the yellow-green, with maximum response at about 5,400 Angstroms and a cutoff at about 5,650. Thus this sensitization does not require a filter to exclude the red. A yellow or yellow-green filter might provide still better detail by excluding the blue and violet.

"The Eastman Company supplies both 548-GH and 549-GH (as well as other spectroscopic emulsions) in both films and glass plates, in several sizes, and with the antihalation backing that is so important for solar work (backing should be specified in the order).

"The Type 548-GH plates are also sold as a regular commercial product under the name Kodak High Resolution Plates. These are not backed, however, and the price is about twice that of the corresponding spectroscopic 548-GH plates.

"In using these emulsions it is particularly important to remove all dust from the plate or film holders before loading, and to brush the plate lightly before closing the holder. The high contrast and resolution of the emulsions make even the smallest dust spots particularly noticeable. Development is best done in a tray with a deep yellow safelight. The emulsions will stand a great

deal of exposure to such a light after they are wet and with a little experience one can learn to judge the state of development by viewing the wet plate with the light behind it. To assure uniform development, first soak the plate or film in distilled water about one minute. Develop in Eastman D-19; exposure should be such that the desired density is reached in about five minutes, but I have obtained good results in underexposed negatives by developing as long as 40 minutes. Rinse in water, fix in acid fixer and wash thoroughly as usual. Water and solutions should be at about 68 degrees Fahrenheit.

"Solar photography, like all astronomical experimentation, is good fun. But let me close on a note of caution. Nothing could seem quite so harmless as a small telescope, and the instrument always attracts visitors of all ages who are ready to seize on any brief opportunity to peek through the eyepiece. The consequences of such a look at the sun hardly needs emphasizing. I never leave a telescope unattended, even for a minute, when the sun is up. I have found that it makes a healthy impression on an audience to stick a piece of paper into the beam at the exit pupil of the eyepiece and let them see it explode into flame. In this connection it should be noted that the use of a dark filter-glass near the focus for visual observation of the sun is a dangerous procedure. If the glass cracks, the eye is likely to be permanently damaged."

Robert Lawrence and Henry Soloway, students at the State University of New York College of Medicine in Brooklyn, write: "The apparatus for measuring the metabolism of mice described by Nancy Rentschler in your department for August is most interesting. We suggest, however, that comparable results can be achieved with the much simpler apparatus devised by D, T. Watts and D. R. H. Gourley of the University of Virginia Department of Medicine.

"In this apparatus, the rate at which oxygen is consumed by the animal in the test chamber is indicated by the movement of a soap bubble through a calibrated pipette connected to the chamber [see illustration left]. Exhaled carbon dioxide is absorbed by a layer of soda lime on the bottom of the chamber.

"The setup consists of a wide-mouthed jar of approximately half-gallon size fitted with a screw cap into which a graduated pipette is sealed with model cement as shown. The calibrated portion of the pipette which extends outside the cap should have a volume of five milliliters. In operation the jar is placed on its side and the bottom covered with half an inch of soda lime. A platform of wire screening is placed inside the jar an inch above the corrosive lime. The experimental animal is .3 first weighed (in grams) and then placed in a small restraining cage of wire screening. The ends of the cage are closed with crosses of adhesive tape. The caged animal is then transferred to the platform, the jar capped and the edge of the cap sealed to the jar with Scotch electrical tape. The animal is permitted to rest for 20 minutes.

"At the end of this interval record the room temperature (in degrees centigrade) and the barometric pressure (in millimeters of mercury). The inside of the pipette is then wetted by means of a .3 test-tube brush dipped in Aladdin's Bubble Set diluted with three parts of water. The soap film (which is to serve as the indicator) is applied by dipping the brush into the soap solution and drawing it across the end of the pipette. The film will move down the pipette slowly, in response to the animal's consumption of oxygen. Fresh air, to replace the consumed oxygen, flows into the chamber through the pipette and drives the soap film before it. Hence a movement of the film from the zero graduation on the pipette to the five-milliliter graduation indicates that five ml. of oxygen have been consumed by the animal.

"The time required for the soap film to move from the '0' graduation on the pipette to the 'five ml.' is a function of the animal's metabolism. Measure this interval with a stop watch calibrated in 100ths of a minute. Make three such runs, add the three stop-watch readings, divide the sum by three and record the quotient. This is the average time (in minutes) required by the animal to consume five ml. of oxygen. Divide .3 by the average time. This converts the consumption to liters of oxygen per hour. Now multiply the consumption in liters per hour by 273 and divide the product by 273 plus the room temperature expressed in degrees C. This converts the volume of oxygen actually consumed to what would have been consumed at standard temperature (zero degrees C.). Next, a similar conversion must be made to what the consumption would have been at standard barometric pressure. If the barometric pressure of the room is higher than 760 millimeters (standard pressure), multiply the consumption (corrected for standard temperature) by the measured barometric pressure and divide the product by 760. If the measured pressure is lower than 760 mm., then multiply the consumption corrected for temperature by 760 and divide the product by the measured pressure. The consumption is now- adjusted to both standard temperature and standard barometric pressure.

"The remaining calculations are equally simple. Look up the logarithm (to the base 10) of the adjusted consumption. Square the recorded weight of the animal, find the cube root of the result and divide it by 1,000. This gives you the surface area (approximately) of the animal in square meters. Look up the logarithm of the surface area, subtract it from the logarithm of the oxygen consumption and, finally, look up the antilogarithm of the difference. This quantity is equal to the liters of oxygen consumed per hour per square meter of surface area at standard temperature and pressure–the measure of the animal's metabolism.

"We hope this procedure, which is much simpler to perform than to describe, will encourage more amateurs– particularly those of high-school age to undertake metabolic studies."

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