POPULAR ASTRONOMY

Evening Post, Volume LXXXV, Issue 21, 25 January 1913, Page 12

POPULAR ASTRONOMY

) SUN VERSUS THE WEATHER By Miss Mary Proctor. {Specially written for the Evening Post.) | Possibly th^fe Me few questions of more vital interest than the determine l tion of weather forecasts. Weather is closely associated with the amount cff moisture in the atmosphere aftd changes in atmospheric pressure, from day to day i or from month to month, depending in a | great measure upon the changes in air temperature. This is where the sun's j importance in the economy of nature I cannot be too highly rated. He' id the source of light and heat, and upon the latter depends the disposition of atniosphefid pr'essufe over our globe. That I there ia fln intimate" connection between "disturbances on the sun indicated by sun spots and the weather of our planet has b«en suggested, though not as yet proved. This is the problem which is being solved at the solar obsemtories at Cambridge, in India, California, and elsewhere. The amplitude of the diurnftl oscillations of the magnetic needle* varies from day to day, from month to month, and from year to year, but the maximum of the mean oscillation coincides With the sun-spot maximum, and the / mihimum with the minimum. Similarly, the abnormal variation in magnetic needle oscillations and sun-Spot are said to occur together. "When" we come to weather," according to Allingham, "statistics require a considerable amount of judicious manipulation before the least relation can be clearly traced between the maximum sun-spot period and exceptional weather, and not even all tlios© alleged to exist between sun' Spot frequency and perturbations of the magnetic needle are regarded universally *s beyond question." SOLAR ACTIVITY SHOWN IN SUNSPOTS. The fact that the temperature of our atmosphere undergoes ( small fluctuations which t correspond with the sun-spot period indicates that the solar heat radiation varies with the httfiiber of sun»spots. Sir tfohri Hefschel, doubtless prompted by his knowledge of meteorology, suggested thfc possibility that SUfi'spots ftre similar in character to terrestrial 'tornadoes. HoWeVer, it is"' ohly during the past few years 'that the region in th 6 solar atmosphere where these solar tornadoes Occur has been disctoVwed. Sun«sp6ts, as we see them, Arfi phenomena occurring at or near the solar surface. In reality, it is now known that the actual disturbance occurs in the solai' atmosphere, which is very expensive, rising many thousand miles above the surface in the sun. In this atmosphere, which is quite invisible to us, there Are winds and storms similar, to those which we experience on the eArth. In 1852, Professor G. E. Hale. ' the 1 present Director of the Mount Wilson Solar Observatory, invented an instrument h<s called a speGtroheliograph, by means of which he was enabled to obtain photographs of calcium vapour, which floats in the lower level 6f the sun's atmosphere. Such photographs might be compared to mountain' scenery on our planet, •with clouds floating in the lower valley. In 1903, this instrument was modified so as to permit hydrogen clouds in the sun's atmosphere to be photographed. ; These wete found to drift at a' higher level than the calcium clouds, but it was #dt .jyitil, JpO&^ha^ a\ stilt .higher level was attained. tMiTMar'ch, 1908, the violet light of hydrogen Was used daily for photographing the sun,' but now for, the first time experiments- were made with the. red light of hydrogen. It was ,then found that photographs, taken, with this light revealed a hitherto unexplored region of the -sun's atmosphere,' higber than that shown in previous work. In this upper" region occur the whirling storms Which give rise t6 sun-spots. REGION OF SOLAR TORNADOES. . "Thus the solar atmosphere, like the earth's atmosphere," 'according to Professor Hale, "is more or less definitely stratified, so that winds and storms may occur^at high levels which are not ob« served near the surface. In the case of sun-spots, it is possible that we see » phenomenon somewhat analogous to a tornado or waterspout on the earth. If the gases at high levels whirl with sufii' cient velocity they, develop a tube-like extension, which reaches down through the comparatively undisturbed gases at lower levels. At the centre of the storm the expansion of the gases due to their rapid rotation cools them, and thus prodUGes a comparatively dark cloud', which we see in the sttn-spot. The great whirling VOrtex above the spot, however, remains invisible unless photographed with the spectroheliogittph." I MAGNETIC FIELDS IN SUN-SP.OTS. We now know that sun-spots ars caused by disturbances in' the sun's atmosphere, dhd a rapidly increasing collecl tion of photographs is furnishing mate- | rial which will permit a further enj quiry into the nature of stinkpots and t their relationship to" other solar phenomena. ■ Already an important item has i been added to our knowledge on the sub- [ ject. From the experiments of the late j Professor Rowland, made in Helmholtz's j laboratory in 1876, it is known that an electrically charged body, when rapidly ; rotating, produces a magnetic field. Such a field is, similar to that given by an ordinary bar magnet, or by a Coil of -wire through which atl electric current is passing. Every dynamo contains a powerful magnetic field} produced by the flow of the current through the coils of the field magnets. Assuming the existence of electrically charged bodies in the atmosphere of the sun, Rowland's experiments would indicate that theif rapid revolution in Sun-spot vortices should produce a magnetic field. Tests were made in the Pasadena laboratory of the Mount Wilson Solar Using the vapour of iron, for example, it was found that the light emitted by this vapour, when placed between the poles of a powerful magnet, gave just such results ag wel-e obtained in the solar observations, Tests were made with other substances, and the results seem to leave no doubt as to the existence of a magnetic field in sun-spots. - The question now remains whether these magnetic fields on the sun are the cause of terrestrial magnetic storms. Apparently they are not the direct cause, as their/ intensity is greatly decreased a few thousand miles above the disturbed region. Nevertheless, according to Professor Hale, "there is reason to believe that the eruptions associated with sun-spots are more likely than the sun' spots themselves to be the cause of terrestrial storms." This cannot be proved without much additional work, in which the proposed Solar Observatory for Australasia will doubtless take its part.