IN STARRY SKIES

Evening Post, Volume CVI, Issue 46, 31 August 1928, Page 16

IN STARRY SKIES

SOLAR UPHEAVALS CYCLONES AND TORNADOES ' (By "Omega Ccntauri.") Tho Chineso have preserved records 'of the observation of sun spots extending as far back as 301 A.D., but tho belief in tho immaculate character of the solar surface persisted in Europe until 1610, when the newly invented telescope rovealed the existence of sun spots to Fabricius, to Schemer, and to Galileo. The spots were immediately made use of by tho latter in determining.'tho timo of the sun's rotation. In 1843, Schwabe, after about twonty p years of study, announced that their numbers varied in a cycle lasting about cloven years. It was soon noticed that tho variation in the sun's activity, disclosed by ,this cycle, was not without, its effects on earth. ,' Nowadays the ana's surface is kept under constant observation, and is gtudied with the help of most ingenious

»nd extraordinarily powerful instruments. ■ The 150 ft tower telescope at Mount Wilson is armed with a spectrograph sft in length. The light which enters this .spectrograph through a slit only three-thousandths of.an inch wide, after being dispersed by the grating I with 14,000 lines to the inch, is returned i as a spectrum about 40ft in length. With .instruments such as these many , solar secrets have been revealed, but in- ' numerable problems still await solution. ' ' This photograph shows' a great, sun , spot group taken at Mount Wilson on | Sth February, 1917. The size of each ] spot can.be realised by comparing it with the size of the earth, which is indicated by a black dot in the corner of the photograph. A typical spot shows a dark centre, called the "Umbra, and a grey border, called the Penumbra ! Spots are^only dark, however, by com- ' parison with the brilliant surface of the ■ sun. If everything else could be hidden, the spot woul appear' as ■ brilliantly bright. Sun spots are veritable solar cyclones., Their vortices appear to resemble water ■ spouts in shape, a vertical funnel spreading' out like a trumpet above. The.gases in a spot are whirling with terrific fury, matter from below continually rushing upwards."- The rapid expansion and .the work done against gravity cool the gases from about 6000 degrees to perhaps 3500 degrees in absolute temperature.* This lowering of\ the temperature allows'some compounds ,

to form such as calcium 'hydride, magnesium hydride, and titanium oxide. The friction of the whirling gaacs gives thorn electrical charges, and the circling clcctrio'': currents produce powerful magnetic effects. Thcso effects have been intensively studied at Mount Wilson, and Dr. G. X Hale has described some of the resultant discoveries in his delightful littlo book, "Tho Depths of tho Universe." Faraday's wonderful experiments on the relation of light to magnetism and electricity laid tlio foundation of most of the newest advances in physics. Zeemau, with more powerful apparatus, discovered additional effects which Faraday just before his death had sought in vain. These discoveries aro now mado uso of daily in reading the riddles of the sun. The behaviour of metallic vapours under the stimulation of powerful electric fields is studied in the^ laboratory, and the same vapours are* recognised to bo bo- ■ having in tho same way in the atmo-' sphere of the sun.. . The spectral. lines duo to iron, sodium, calcium, chromium, titanium, manganese, cobalt, nickel, and other metals give clear evidence of magnetic polarity in sun spots. In terrestrial cyclones and tornadoes tho .air in tho Northern Hemisphere makes an anti-clockwise or left-handed whirl, whilst'in the Southern Hemisphere tho atmospheric rotation is in the opposite direction. The majority of the hvdroger vovticos above sun spots

conform- to these directions in both hemispheres, but the magnetic polarity at lower levels follows different laws. Spots very frequently occur in pairs. In nearly all cases the preceding spot is opposite in polarity, to the following one. But at any one time the -preceding in the .Northern Hemisphere have the1 opposite polarity to those in the southern. But this is not all. The polarities are all reversed in the succeeding, elev'enyear cycle. From 1908 to 1913, for instance, the preceding spots itt the Northern Hemisphere were .of south seeking polarity, whilst those following were of north polarity.. In the Southern Hemisphere exactly the opposite arrangement held. In the next cycle the order in each hcinisph-rc, v was exactly reversed, and in the following cycle, of -which the iirst spot appeared jin 19212, the original arrangement was I returned to. It thus appears that the complete magnetic cycle takes a little over .twenty-two years for its completion, ' although the average tinio from maximum 1o maximum, or from minimum to minimum, is only 11.13 years. j Sometimes a single spot is seen without any visible companion. This fact led to a very-remarkable discovery, and enabled astronomers in certain cases to foretell the outbreak of a solar storm. Dr. Hale found that hidden cyclonic disturbances were revealed by the effects produced on the, emitted light by magnetic forces. These deep-seated hidden storms sometimes manifest themselves later as visible spots on the sun.