No individual observer can see far enough to comprehend at any instant more than a small fraction of the planet's total geophysical pattern. As Lloyd V. Berkner, vice president of the Special Committee for the IGY, has pointed out, man's existence so far has been confined within a veneer at the surface of the earth about as thick, relatively, as the map paper covering a 12-inch globe. We can dive to the ocean's floor or dig holes in the earth about five miles deep. A rocket-powered plane recently carried an observer to an altitude of 25 miles. These excursions represent the present vertical limits of our firsthand observations. Within this relatively thin zone we can, at least potentially, roam the surface of the planet at will. But few observations at any one site are descriptive of the whole. The atmosphere and oceans are in complex fluid motion; sunlight, which powers terrestrial phenomena, falls unevenly on the surface of the earth; the forces at work in the interior constantly reshape the crust in varying s; amounts at unpredictable places and . times. Accordingly, the only hope of answering the many unanswered questions . Of geophysics lies in gathering and analyzing the simultaneous observations of many scientists working in collaboration throughout the world. There are simply not enough scientists available for the job. Hence, if the objectives of the IGY are to be fully attained, amateurs must lend a hand.

One of the many facets of the IGY program to which amateurs can make a contribution is the observation of auroras. Under certain favorable conditions the night sky, particularly in the h latitudes within about 20 degrees of the . earth's magnetic poles, fills with magnificent displays of pastel-colored light called the polar aurora. From remotest times auroras have been a mixed source of mystery, awe, terror and delight. They have been ascribed to every conceivable cause from gods locked in battle to the bombardment of the atmosphere by solar debris.

Auroras are grouped in three main classes: rayed, homogeneous and pulsating. Fredrik Carl Stormer of Norway, the first dedicated student of auroras, h subdivided their forms into arcs, bands, draperies, coronas and flames. It is now generally agreed that auroral displays are caused by energy from the sun. Some specialists suggest-that the glow arises when jets of high-speed solar particles ionize the upper atmosphere by collision in a reaction like that observed in gas-discharge tubes. Others hold that the ionizing energy comes from ultraviolet rays liberated by the sun. Both ideas will be investigated during the IGY, along with numerous other questions. Do auroras occur in the daytime?

How are they associated with geomagnetic storms? Why do some auroras penetrate to the low latitudes? Do auroras occur simultaneously at the North and South Poles? Do they ever meet at the geomagnetic equator? Such questions are broadly significant because auroras act as visual indicators of incoming energy and can serve as instruments for measuring and analyzing the effects of at least some portion of the total energy received from the sun.

Sydney Chapman, president of the Special Committee for the IGY and coordinator of the auroral program, writes the following review of the plans.

"I am glad to say that the IGY auroral program for the high latitudes is now well organized, both in the Arctic and the Antarctic. There will be networks of all-sky cameras, research by spectrographs, radar and other microwave apparatus as well as comprehensive coverage by visual observers.

"These facilities, however, will not cover the cases which are in some respects the most remarkable–the auroras that accompany great magnetic storms and extend far beyond the usual geographical range into the lower latitudes, sometimes even into the tropics. Many countries lying in the middle and low latitudes have failed to organize auroral programs, under the mistaken impression that the phenomenon never occurs in their locality. My object in addressing amateurs through these columns is to correct this impression and enlist their cooperation

"It is not certain, of course, that there will be even one tropical aurora during the IGY. It is known, however, that they are most likely to occur in years when the sun is especially active and spotted, and it is expected that the IGY will span such a period. Moreover, a careful watch may prove that tropical auroras are not so rare as presently supposed.

"The warning notices will be of two kinds. The less urgent will announce 'alert' periods; the more urgent will proclaim 'special world intervals.' Alerts will be announced when the state of the sun indicates a growing activity likely to result in auroral, magnetic and other terrestrial effects of more than average interest. Solar activity that seems likely to result in intense and widespread terrestrial effects will call for the proclamation of a special world interval. During these intervals the full resources of elaborately equipped observatories will go into action on a 24-hour basis.

"The warnings are designed, of course, to economize the time of observers. It is hoped that observers will cover both types of warnings, but particularly the special ones, when the watch has the greatest chance of being fruitful.

"The auroral watch will be shorn of some of its value if confined to the early part of the night. It is hoped that nightlong watches will be kept. Night workers who are regularly up between midnight and dawn and who can devote some time to observing are especially urged to participate in the program, particularly those who live in the tropics or whose work takes them into rural areas of the low latitudes.

"In addition to the world prediction and warning center, it is hoped to form a world-wide organization, consisting of one auroral reporter in each participating nation, for handling auroral reports from individual observers. Each reporter will collect and forward the observations to the auroral data center. The names and addresses of auroral reporters will be made available to interested amateurs through their respective national IGY committees. Canadian amateurs who wish to participate in auroral work should communicate with Peter M. Millman at the National Research Council in Ottawa. U. S. amateurs should write to Carl W. Gartlein at Cornell University in Ithaca, N. Y.

"The amateur will need little if any special equipment for participating in the program. Any device that improves the accuracy of the report, however, will add to its value. A navigating officer at sea, familiar with the compass and sextant, can obviously make better measurements of the angular elevation and azimuth of auroral features than an observer who relies solely on his eyes. It is hoped that many observers will find it possible to improve the accuracy of their estimates by erecting one or more poles with pegs inserted at calibrated intervals of elevation with respect to a spot to be occupied during observations.

"Amateur astronomers who are familiar with the sky will be able to specify the position of auroral features with reference to the constellations. The precise time of observations must be given in all cases, of course.

"In the higher latitudes amateurs may wish to equip themselves with light filters for isolating particular colors of the auroral radiation. Suitable filters enable you to see auroras in bright moonlight or near sunset or dawn far more clearly than is possible by the unaided eye. The auroral spectrum in the visual region is dominated by two colors emitted by excited atoms of oxygen–green at 5,577 Angstroms and red from a pair of closely spaced spectral lines at 6,300 and 6,363 Angstroms. Absorption filters that favor these colors can be purchased from photographic supply dealers for a few dollars. Observations of low-latitude auroras made with interference filters capable of giving more precise information about the spectral composition of sections of the displays would be of great interest. In addition to enhancing the value of observations, filters and pocket spectroscopes (because of the special qualities of auroral light) can aid observers in all latitudes in detecting auroras hidden by clouds. This was dramatically demonstrated on September 25, 1909, when clouds obscured an aurora from observers in London. Its presence was readily detected by means of a small pocket spectroscope.

"Photographs also can be of great value. The exposure should include background stars or other positional references such as calibrated poles. So Ear as I know, the lowest geomagnetic latitude from which an auroral photograph has been made was in Greece. The aurora appeared in a plate exposed by W. N. Abbott of the Athens Observatory on the Greek island of Spetsai just before dawn on August 19, 1950. He was recording the zodiacal light with an astrographic camera. Abbott thinks it likely that the aurora occurred near the end of his 25-minute exposure. Its presence on the plate was not suspected until the plate was developed weeks later. The aurora was almost due east from the island. I have made many inquiries without success in an effort to unearth photographs of other low-latitude auroras. Amateurs resourceful enough to shoot one during the IGY will have bagged a rare prize.

"Even before the IGY begins, amateurs can join in a project which merits enthusiastic support. This is a search of historic records for observations of past auroras. An item found recently in the New York Times for August 29, 1859, illustrates how rewarding such a search can be. It said: 'New York–An Auro Borealis-of extraordinary brilliancy and extent lighted up the heavens last evening and filled the streets with admiring crowds of upturned faces. The auro began to appear in the northwest about half-past seven and increased in brilliancy until half-past ten, when it gradually disappeared. The bars of light were at first horizontal but they afterwards assumed a vertical form, flashing with amazing luminousness and extending from the southwest to the northeast; on opposite sides of the heavens. There were at the same time luminous masses of a brilliant formation producing a most singular effect. There was a fresh northwest wind at the time and the atmosphere was very cool.'

"Similar accounts can be recovered from newspaper and magazine- files, libraries, diaries, letters, the minutes of scientific organizations, historical societies, entries in ship logs and so on. A few countries have collected records of auroras seen locally. Such a project would indeed constitute a valuable enterprise. One of the best collections ever made on a world-wide basis was assembled in 1873 by Hermann Fritz, professor at the Zurich Polytechnic Institute. It covered the period from 503 B.C. to, 1872 A.D. From the collection Fritz established that in the Northern Hemisphere auroras occur with highest frequency in a belt about 20 degrees from the geomagnetic pole. But his records also disclosed a liberal sprinkling of auroral observations farther south. They indicate that an aurora appears in the tropics about once in 10 years.

"The aurora mentioned in the New York Times was one of the greatest on record. From August 28 through September 2, 1859, there was a violent outbreak of sunspots and solar flares, and for several nights before and afterward auroras were intermittently widespread over the globe. They were brilliant in Honolulu.

"Another great tropical aurora occurred on February 4, 1872. This display was seen from Bombay and seven other places in India between the latitudes of 27 degrees and 36 degrees North. Other tropical places from which it was seen include Santo Domingo, Guatemala, Aden, the West Indies and, in the Southern Hemisphere, the islands of Reunion and Mauritius. Many of the descriptions of it are vivid and striking. This aurora was accompanied by an outstanding magnetic storm which for some hours interrupted or disturbed telegraphic cable communications all over the regions of the globe where such facilities then existed.

"During the present century there have been several outstanding auroras. One, which accompanied an intense magnetic storm on September 25, 1909, was observed at Singapore, just one degree north of the Equator! It was also observed at Batavia, six degrees south of the Equator.

"There was a tropical aurora on May 13, 1921, about four years after the sunspot maximum of 1917. It is interesting that of the 12 greatest magnetic storms occurring within the past 81 years, three fell approximately four years after the sunspot maximum. The great aurora of 1872 followed the sunspot maximum of 1870 by about a year and a half. In contrast, that of 1859 preceded the sunspot maximum by six months. The 1921 tropical aurora was observed from Samoa and from Tongatabu, 14 degrees and 21 degrees South latitude.

"It seems likely that other tropical auroras have occurred during the present century, but I have been unable to locate records of them. Our known records of the great auroras of 1859, 1872, 1909 and 1921 are woefully fragmentary and inadequate, although the displays were doubtless observed by tens of thousands of people, perhaps even by millions. As in earlier times, many residents in low

latitudes may have viewed these strange appearances in the sky with superstitious awe, unaware of their nature and scientific interest. But some observers doubtless made careful accounts of what they saw. The files should be searched carefully for those great auroras.

"It is not surprising that records of the past auroras are scarce. Their significance was not widely appreciated–even after the great contribution of Fritz. I, too, am guilty, having started the collection of data for the 1872 aurora only within the past few years. Though I have been interested in magnetic storms since 1917, I made no attempt to interview observers at the time of the 1921 tropical aurora. In 1954 I tried to collect information about it from Tongatabu, but it was too late: memory had faded. Better success attended an effort to recall observations of the 1872 aurora in India. Through the kindness of Indian friends, I recovered some valuable contemporary newspaper accounts.

"There have been 18 great outbreaks of auroras in the past 109 years [see table above]. Any references to them by observers, however brief, would be helpful. Amateurs in all parts of the world are urged to thumb through all promising records for the dates indicated. The project should not require many hours. All findings should be forwarded to D. S. Kimball at the Yale University Observatory in New Haven, Conn. With this amateur contribution we may recover some thrilling accounts, which would otherwise be lost, from the generations of men who had the rare fortune to behold these great natural spectacles."

Peter D. Johnson of Schenectady, N. Y., is one of the many amateurs around the world who are preparing to participate in the visual tracking of the earth satellites to be launched during the International Geophysical Year. Part of his preparation has been the construction of a telescope of the "rich field" type designed for satellite observing.

"The mirror of the instrument," he writes, "is eight inches in diameter with a 29 1/2-inch focal length. This focal ratio, about f/3.7, means that the mirror requires careful parabolizing, of course, because of its deep curve. The low power at which the telescope is to be used, however, imposes a somewhat less stringent requirement on the shape of the curve than in the case of conventional instruments designed for observing stars. The mirror is held in place by means of six Z-shaped brackets fastened to a wooden hexagon which fits inside the plywood tube of the instrument [see drawing right]. Rubber tubing slipped over the Z-strips protects the

mirror from the metal. The strips make a snug fit but do not exert enough pressure to strain the mirror. The hexagonal mount is fastened at the end of the tube by means of wood screws inserted through longitudinal slots in the tube. The slots provide adjustment for aligning the optical system. The alignment is made only once, hence the adjusting mechanism need not be elegant.

"For the eyepiece I use one of the inch-and-one-quarter eyepieces advertised by the Edmund Scientific Corporation. In combination with the mirror it yields a field of view approximately three degrees in diameter. The off-axis aberrations of the mirror and inadequacies of the eyepiece impair the quality of the image somewhat as the edge of the field is approached. The good portion of the field, however, is more than adequate for the average eye.

"The tube is made rigid by fastening the six side-pieces of plywood together with 120-degree brass strips and by gluing small triangular pieces of plywood inside. The tripod is made of two-by-fours braced with aluminum pipe and beams from a defunct aluminum clothesline tree. The equatorial mount on which the tube rotates is made of two-inch pipe fittings. The threads comprising the bearing surfaces in declination and right ascension were lapped with 600-mesh Carborundum, followed by 303 emery and finally coated with beeswax for smooth operation. The counterbalance weight is an eight-pound sash weight placed inside the capped pipe opposite the telescope. The instrument was made without the aid of machine tools other than an electric hand drill. All parts except the optics are available at your local hardware store and lumberyard.

"This is the fifth reflecting telescope I have made and put into operation. A six-inch f/5.6 is my most professional mirror so far. I have an eight-inch f/5.6 with a four-inch f/7.5 guide telescope adapted for photographic work and a four-inch f/13 unaluminized job with which I am experimenting in the hope of using it for solar observation during the forthcoming sunspot maximum.

"The generally short focal length of my mirrors is dictated by the miserable seeing conditions prevalent in Schenectady and the resulting necessity for portability. My tendency to inelegance and simplicity is dictated by the lack of machine tools and by my experience as a physical chemist in an industrial laboratory, which has shown that by designing equipment to do the jobs you want to do–and no more–it is possible to eliminate much unnecessary complexity.''

Bibliography

AMATEUR TELESCOPE MAKING: BOOK ONE. Edited by Albert G. Ingalls. Scientific American, Inc., 1950.

THE AURORAE. L. Harang. John wiley & Sons, 1951.

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