Popular Science Monthly/Volume 59/May 1901/The Aurora Australis, as Observed from the Belgica
|THE AURORA AUSTRALIS, AS OBSERVED FROM THE 'BELGICA.'|
IN the literature of the still unknown phenomena of polar auroras, deductions have been based almost entirely upon observations of the aurora borealis. So little has been known of the south pole and of its terrestrial and celestial surroundings that the aurora australis has been omitted in the upbuilding of auroral science. From the observations of the Belgian expedition and from the reports of forgotten previous explorers, it would seem that the auroras of the south are not so brilliant or so varied in form and character as those reported from the north. Auroras in brilliant colors and in fantastic heavenly drapery are indeed rare in the regions invaded by the 'Belgica.' It should, however, be remembered that the austral phenomenon is but vaguely known. The 'Belgica's' drift covers but a small space in the great unknown area about the south pole. Nearly eight million square miles, a region as large as all North America, is still a blank under the Southern Cross. At other points within this area the aurora may appear differently. Such a condition obtains in the arctic. Nordenskiold, viewing the northern lights from the sea north of Siberia, saw displays almost exactly like those seen from the 'Belgica' south of the Pacific, but Peary and all the explorers who wintered on the Greenland side of the geographical pole have described auroras in vivid colors and fantastic forms.
The antarctic continent, which is just the region from which the southern lights can best be studied, is still unexplored, and most of it is inaccessible. If we can judge from similar latitudes in the north, the edge of this great continent of ice is an ideal latitude for effective observatories, and no doubt future explorers will seek favorable locations from which to observe this curious phenomenon.
The inhabited parts of Australasia, southern South America and Africa are too far north to offer a good station to study these phenomena. There are no convenient land projections in the antarctic, like Siberia, Norway and Greenland in the arctic, where comfortable stations could be established. From this it results that few careful studies of the austral aurora have been made. The great restless, unencumbered sea which sweeps around the south polar area is not favorable for such observations. Captain Cook, who, during three years, circumnavigated the globe in high latitudes, barely mentions the aurora. Ross, Wilkes and d'Urville were in the ice regions only during the days of summer, when auroras were seldom visible.
The early sealers, who in the first quarter of the last century invaded the lonely southern seas, rarely mention the aurora. From the observations of the sealers and the early explorers it would seem as if we should have a fair idea of the austral auroras, but all antarctic voyagers have devoted most of their time to skirting the edge of the pack-ice, where the sky is almost constantly veiled by a haze of either fog or snow. The fact that the pioneers in the far south have seen so little of the aurora has led to the impression that the phenomenon there is feeble, but such an impression should not be favored until we have a more thorough series of observations.
Ross and Wilkes saw a few vivid displays of draped auroras, tinged with prismatic colors, but from the 'Belgica,' which was the first vessel to spend a winter in the antarctic, we saw few colors, seldom draped, and only rarely fleeting rays which spread over a large part of the sky. Below is a table of the observations recorded by Henryk Arctowski, the meteorologist of the Belgian expedition:
|10||—||A.S. Ad.||—||A.||L.||—||R.S.A. Ad.|
|19||Am. V.P.||—||—||—||—||Ad. S.||—|
|A.=Homogeneous arc.||C.=Crown.||O.=Obscure rays.||S.=Dark segment.|
|Ad.= Double arc.||F.=Flames.||P.=.Streamers.||V.=Wavy ribbons.|
|Am.=Multiple arc.||L.=Luminous glow.||R.=Rays.||W.=Curtain.|
In the 'Belgica' we had been sailing among icebergs and along the ice-sheeted coast of newly discovered lands for nearly two months before we saw the first aurora. During most of this time we were above the polar circle, where the sun, during the hours of midnight and midsummer, sank but a few degrees behind the icy crust of the earth, leaving a twilight so brilliant that no stars were visible. The glancing rays of the nocturnal sun, which were thrown from peak to peak and from the mirror-like slopes into the heavens, made the night a scene of dazzling splendor, too bright to permit the display of the auroral light.
In the first days of March we found ourselves surrounded by a hopeless sea of ice from whose ensnaring influence we were unable to extricate ourselves. The long winter and the polar night, which no man had as yet experienced, now came over us rapidly. The sun daily sank lower on the sky and swept less of the horizon. The rose color of the snow, which made the summer nights charming, now changed into lilac. The open spaces of water between the restless ice-fields were being hidden lender a weight of rapidly forming new ice, and the winds were moaning in prophetic despair of the coming blackness. We knew only too well that we were in the relentless grasp of a new monster, the Antarctic Ice King, and in his grasp we must remain until the thaw of another summer should release us. In this spirit of despondency and with considerable anxiety we searched the skies nightly for the heavenly glow of the aurora australis, which we hoped might relieve the awful monotony and soul-despairing darkness of the coming winter.
While skirting the edge of the pack-ice late in February we saw a star, the first since leaving the Cape Horn waters, and this little speck, though a sign of the long, gloomy night and of the polar winter, was hailed as a messenger from a new world. During the days which followed we watched with joy the increasing number of stars from night to night, but there was so much storm and the atmosphere was so thoroughly charged by humidity that a clear sky was rarely observed.
On the evening of March 12, 1898, we saw the first distinctive aurora. A faint arc was seen the night previous, but the light was so feeble that many of us doubted that the phenomenon was auroral. The few days which preceded were clear, sharp and cold. We had been so constantly showered with snow and sleet, so persistently held in banks of fog and so often driven to the verge of desperation by the violent storms which ever swept the pack-edge that this calm and silence was, indeed, a treat to us. On the evening of the 14th the sun sank out of a cloudless sky below the crackling, quivering ice of the sea. The temperature was - 15 C. A light wind, which came out of the south, pierced the skin like needles. We were many hundred miles from the nearest land; our horizon was everywhere lined by the towering heights of icebergs which were separated by level fields of sea-ice.
Over this sheen of hard ice and soft snow there rested a haze of ice crystals which was curiously suspended in the air. As the sun sank through this haze it lost its luminous character, and before it vanished into its bed of snow it appeared as a great, distorted, rayless ball of crimson. The play of light in this icy haze is a joy experienced in no other part of the globe. Over the departing sun there remained a band of orange running into rose at the sky line and into gold at its upper edge. At the same time there rose in the east an arc of dark purple-blue, edged with orange. This is the twilight curve which is here strikingly noticeable. As the purple of twilight ascended towards the zenith, the snow westward had a delicate lilac hue, and eastward there was a bright purple-blue over everything, which finally deepened into a gobelin-blue.
At about eight o'clock the Southern Cross was clearly visible over the masts. The purple twilight curve was absorbed into the homogeneous blue of the, sky. At the zenith there were a few waves of light which had the appearance of high cirrus clouds. These darted across the heavens with lightning swiftness, fading, vanishing and reappearing with augmented force each time, until at ten o'clock the phenomenon settled into a waving, luminous arc with a fringe, causing it to look like a curtain hanging low on the southern sky. Still later the fringe work gave place to a steady luminous arc, whose highest altitude was about 30°.
The evening of the 14th was also clear and calm. There was a fascinating sunset, followed by a long purple twilight. The temperature had fallen to - 20 C. The glassy character of the air, the paleness of the sky and the absence of wind were to us indications of a very cold night. Such nights are always favorable to auroral displays, and we were early on a lookout for them. At about nine o'clock there appeared a bank of luminous fog in the southwest. Soon after, there rose an arc over this which was at first imperfect. Now the eastern portion was illuminated, then the western portion, and, again, only a fragment of the center was visible. So rapid were these changes that we found ourselves unable to record the fleeting forms.Everybody was on deck or pacing the ice about the 'Belgica,' making notes and sketches of the phenomenon. The scene was such as would delight the heart of any lover of nature. The good old 'Belgica,' the home of the only speck of human life within the icy under-surface of the globe, was buried in a bed of snow which so completely covered her body that only the rigging projected. Even the masts and the ropes were encased in a heavy plating of hoar-frost and hard ice, which glittered like gems in the silvery light of the
night. As we walked around the bark in an unsuccessful effort to keep warm we saw beyond the glittering spars the glow of a great arc. This, for a time, hung steadily between the masts and then suddenly, as if the fetters which had held it together had burst, the entire southern heavens were swept by aimless bands of fleeting luminous patches.
After a violent storm which lasted for three days the sky cleared again on the evening of the 19th; the wind then came in puffs with doleful wails like the moans of a dying soul. This we knew indicated that the tempest was nearly spent. At five o'clock I wrote in my log:
"5 P. M.—The storm has at last abated. It has left us so suddenly that the calm is as unexpected as it is appreciated. The barometer is steady and the temperature is falling fast. It is already 9°C., and is still falling. The scene now before us is full of new delights. The ice is spread out again, bright, soft and tinted with delicate colors. Every time the thick air and the gloomy storm clouds are brushed away, the pack, white and sparkling, has a new story to tell. It brings to us moods like a cheerful page in a sad story. Under the influence of this spell everybody is singing, whistling and humming familiar tunes; all are planning new work and nursing big ambitions. In the cabin the music-boxes are grinding out favorite music, which rings over the pack with a new joy. In the forecastle the men are dancing and playing the accordeon with telling effect. From some invisible point of the pack there comes a weird response to every discord of the music. It is the 'gha-a-ah, gha-a-aha' of the penguins. We have had a peep at the sun, and this has brought about an intoxication akin to alcoholic stimulation, and well it might, for the brief period of its visibility has been a dream of charms. The great twilight zone of purple, fringed with violet and orange and rose is rising over the east. The zenith is pale blue, studded with a few scarlet and lavender clouds, and the sun, a great ball of old gold, is sinking under the pearly rose-tinged line of the endless expanse of ice."
"8 P. M.—The ice shows signs of strong pressure from the north. Along the crevasses, running easterly and westerly, there are great lines of hummocks from four to eight feet in height. The colors of the pack are now far from the despairing monotone of yesterday. The yellow sea algæ have already fixed themselves in the new ice and make it appear ocherous. The twilight on clear nights is extended by the latent luminosity of the snow. The blueness of the pack in this twilight, separated by the ebony lanes of open water and decorated by the algæ-strewn yellow and green lines in the hummocks, makes the scenes curiously attractive. Added to this we have the bergs, tall, sharp and imposing, standing out against the soft blue of the sky and the hard blue of the pack as if cut from huge masses of alabaster. The whole scene is one of lively contrasts, pleasing to the eye and stimulating to the mind, having quite the reverse of the effect of the days of darkness and depressing storms which have preceded."
At about ten o'clock we saw an aurora. It began as a ragged arc, spread easterly and westerly across the southern sky, with a straight line running under it close to the horizon. The space under the arc was noticeably darker than the surrounding sky, and in this space, also a straight line, were four luminous spots. The color of the aurora was a bright cream with an occasional suggestion of pink.
There was no noticeable reflection of light on the snow, A quick and constant transformation took place in the form of the phenomenon. A wave of light ran through the luminous bands and spots from east to west. Some parts brightened and enlarged, others darkened and faded away. The arcs were generally of a steady rayless brightness; the apparent movement and wavy effect of light were in a series of sharp rays on a film-like display before the arc.
I found it difficult in the low temperature to remain outside for periods sufficiently prolonged to catch the minute changes in force and character, but I made a series of eight sketches at intervals of about twenty minutes apart, which illustrate the most striking changes. The second form was a homogeneous arc with a fragment of a second arc under it. This hung for some time, with a steady nebulous glow between it and the one previous, as well as between the intervening periods of all. The following typical forms then were rapid and almost imperceptible gradations. The third sketch represents the same position on the heavens; but under it are portions of two other arcs and a suggestion of a luminous horizontal line. At times a wave of rays, converging to the pole of the circle described, ran over the main arc. In the fourth sketch there are two arcs and a portion of a third which were seen persistently in all the exhibits to be present. In the fifth there is a second arc crossing the first. This was suggested by the
March 26. Early Display. This was Followed by Darting Rays and Wavy Ribbons which Ended in a Brilliant Arc with Moving Ray's Drawn Over it Converging to a Common Center, as Shown Below.
third, and it reappeared in the seventh. The sixth form was an arc with three ribbons of luminous beams waving from side to side. The exhibit ended with a plain arc aglow with a steady light.
For a week following we had faint auroral displays every night, but we seldom saw a brilliant or extensive exhibit. The usual form it took at this time was that of a fragment of one or several arches. On the night of the 26th we saw the usual auroral patches in the southeast which we had seen so often before. These disappeared entirely at ten o'clock, but reappeared shortly after in a manner and vividness worthy of note. There was a steady luminous bow somewhat brighter than the Magellanic clouds, and over this there were bunches of brighter rays with a rapid motion from east to west. These rays centered to a point below the horizon. Under this main arc there was from time to time a suggestion of a second and also a continuation of the same rays which played over the main are; above there were also occasional fragments of an arc and a prolongation of horizontal rays. This display continued until about three o'clock in the morning.
The color of this aurora, as of all those which preceded and followed, with but one exception, was a faint flesh color edged with a pale greenish-yellow. We saw no prismatic colors. The exception was a fragment of an arc in the southeast early in the evening of April 10. This was for a few moments noticeably green, but it quickly faded and vanished. Later in the evening it reappeared in the same form and place, but the color was nearly white.
In the latter part of April we saw a few auroras, especially after storms, on clear nights, but instead of increasing in number and in brilliancy, which we expected, as the veil of winter darkness was spread over us, they diminished steadily as the long night advanced. On May 17 we saw the autumnal sun for the last time. Its cold, distorted and seemingly wrinkled face lingered for a few moments on the northern ice and then sank into the frozen sea, from which it did not ascend for about seventy days. It is curious that we must say about seventy days, but this uncertainty is due to the fact that for several days before sunset the sky was obscured by storm clouds, and our constant drift with the pack-ice made our latitude uncertain.
During this long night auroras were but rarely seen, but the weather was clearer and steadier than before and after. On May 21 and 22 there were faint auroral bands in the south, on the 20th there was a feeble arc in the southeast, and on the 29th there was a feeble double arc. On the 22d, 23d and 24th of June there was a similar phenomenon in the same position, and this curiously enough reappeared one month later, in July, on the same dates. The long antarctic night, then, as experienced by the observers of the 'Belgica' was not apparently lighted by the Aurora Australis.
During August we saw but one bright display, which was a double arc, on the 20th, for most of the month was so stormy that the clear sky was seldom visible. The last week in August, however, was a remarkable period of clear weather. Bright sunlight, charming moonlight and fascinating halos were among our delights in these life-giving days of the south polar spring. The sea of ice was made doubly interesting by the increasing number of penguins and seals, crying and grunting and making manifest in various ways the contentment and satisfaction of the new sunny splendor of their usually cold and cheerless abodes. From the 'Belgica' the budding passions of a new life were bursting forth; songs and laughter and a noisy commotion were audible and visible during the evening hours.
The moon often so illuminated the skies that it was difficult to distinguish between ordinary cirrus clouds and bands of auroras. On the evening of September 2, however, there was an exhibit which could not be mistaken, I give it as written down at the time.
"Low down on the southern sky there stands a faint arc of light, and under it there is a distinct segment, darker than the sky above. This segment has been noticed in several previous auroras, but it was
not before so clearly defined. On board there is considerable difference of opinion about this segment. Some have previously doubted its existence, but to-night it is indisputable. I have taken the ground that it is produced by the haze of ice crystals which always rests over the ice, and I believe that its darkness depends upon the amount of humidity or the thickness of the suspended icy haze. The stars shine through this dark segment, apparently as bright as those above, but the light is changed in color and there is frequently a kind of halo about them. The arc gradually grows in intensity and in breadth, and it also rises a little towards the zenith. The upper edge of the segment pales as its height increases. The arc has remained perfectly regular; its two ends almost touch the horizon, and they advance to the east and to the west, widening the distance between them and showing more and more the contour of a circle as the bow of light rises."
For the first hour no beams were discernible, but the whole display consisted of an almost uniform light of a delightfully soft, cream color.
At ten o'clock this arc was about 15° above the sea; it was about thrice the breadth of an ordinary rainbow, and its edges were clearly defined against the dark blue of the heavens. Up to this time an air of restfulness and repose was about the phenomenon, but now this began to change to an atmosphere of mysterious excitement. A wave of light rolled slowly from one side to the other. This wave soon took on the texture of torn lacework and was drawn to and fro, while the arc, which was less brilliant, remained as it had been before. At about eleven o'clock a second arc, somewhat narrower and less brilliant, appeared below the first. The play of drapery now vanished, but in the dark segment there appeared many glowing elongated spots all pointing toward a common circle below the horizon. These came and went with such marvelous swiftness that it was difficult to follow their forms with the eye. Still later, all signs of the aurora disappeared, except the primary arc, which had for a time at its lower edge a faint suggestion of prismatic colors. This rested motionless on the midnight heavens until about two o'clock, when it slowly faded, but before it disappeared it was replaced by a bewildering display of a rayed arc.
From September 1 to the 9th the temperature steadily fell. On the 8th the thermometer registered—43.1 C. This was the coldest spell of the year, and it was followed on the 9th and 10th by the most vivid and impressive auroral displays that we saw. The exhibit of the evening of the 10th began in quite the usual way, with a cloudless brightness in the south. Soon there appeared an arc with its ends about 10° above the ice. Under this arc there appeared three fragmental arcs. In the course of an hour the first arc nearly disappeared, leaving only a crescent strip, but under it there were bows more or less elliptical. These vied with each other, alternately brightening and fading, and
vanishing altogether or in parts, until after midnight. At about one o'clock they disappeared suddenly and in their place came, with an electric glow and swiftness, a bewitching array of ragged patches describing four arcs. One hour later these spread over the entire heavens, making a system of quivering, moving streamers, sweeping the skies and illuminating the snows with an effect perfectly bewildering.
This was the last great aurora that we saw, and it was followed by only one other, on September 20. The night at this time was so bright that the phenomenon was barely visible, but its form was different from any which we had seen. There were two horizontal bands; between these was an imperfect arc, and on both sides were crescent shaped patches. The whole display came and went within an hour.
It is a curious fact that the auroras usually appeared about the 20th day of the month. During the long polar night, when the boreal display is at its best, we saw very few exhibits. The phenomenon had little or no effect upon the compass, but it seemed to have some connection with the storms, for it was invariably either preceded or succeeded by violent atmospheric agitation. We did not hear any sounds, nor conld we at any time perceive an odor, both of which have been reported in connection with the northern lights.
A phenomenon which displays its glories in skies so remote and under conditions so mysterious cannot fail to excite popular interest. This interest generally suggests the question, 'What is the aurora?' This was the inquiry of ancient, as it is still the query of modern students, and our answer is the repetition of the old question, 'What is it?' We are still far from a solution of the problem. We have, however, advanced far enough to put aside many old theories, and we hope that we are now on the train of inquiries which will eventually solve the mystery.
The similarity of auroral light to that generated in a vacuum bulb by the passage of electricity, it is now believed, lends support to the proposition, suggested long ago, that the aurora is of electrical origin. It was expected that that great mystery-solver, the spectroscope, would help us in this matter, but it has only served to add further mystery to the subject. For the line which it sifts from the aurora is not matched by any other known substance. A similar line is found in the zodiac light, but this does not elucidate the matter. The zodiac light, though better studied, is still as mysterious as the aurora. When electricity passes through rarefied air it exhibits a luminous stream which seems to have the characteristics of the aurora, hence it is quite probable that this natural phenomenon is the result of currents of electricity passing through the upper regions of the atmosphere, particularly by an exchange of celestial and terrestrial electricity.
The question is, however, one of the problems of the future. Though many exploring expeditions have penetrated the icy polar solitudes, very few men have given the time and patience necessary for a systematic study of the aurora. No travelers should enter the realms of the polar lights without being prepared to record, with the accuracy required by science, the plays of this heavenly mystery. I believe that, when men shall have penetrated a little farther southward into the unexplored area about the south pole, the aurora australis will be found just as brilliant, as varied and as frequent as the aurora borealis. With our present marvelous strides in uncovering the accumulating mysteries of past centuries, we ought, ere long, to look with pride and understanding into the dark vault of the polar night and read the flaming letters which must there reveal a thrilling tale of Nature's most cherished secrets.