IN STARRY SKIES

Evening Post, Volume CX, Issue 117, 14 November 1930, Page 14

IN STARRY SKIES

ASTRONOMY FOR GIRL GUIDES

THE GALAXY

(By "Onioga Centauri.") The-stars are not strewn ut-.random j iv the heavens. The brighter ones, it is true, appear to bo scattered rather irregularly and without much evidence of plan, over the greater part of the sky. But this is because they are comparatively near to us and we are in the midst of them. The majority of the.fainter stars are mucl^ more symmetrically placed. They seem to. crowd about the wonderful baud of light we call the- Milky Way. On a clear, moonless night- this is a glorious sight. >We can see half of-it or, more.at.'any timo ■! of the year, but in the early, evening throughout November it is not' seen to advantage,- as then it almost circles the horizon. • By.; the.. N!ew iYear the- eastern portion, will have, risen ;half-\vay. to the zenith and'the'luminous band will extend right from the horizon in the north to that in the south. In March, at the same time, it will pass, through the zenith. By May it will extend from east to west. In.July a.different portion will bo in the zenith and the band: will pass from: N.E.. to • S.W. A '

fine string of constellations lies along it. From Andromeda, Perseus, and Auriga, which are too far north to be well seen, the Milky Way passes between the Twins on ono side- and the Bujl and Orion on the other. It goes just besido the Great Dog and enters "the enormous constellation Argo. Then in succession it passes through the Cross, the Centaur, the Scorpion, the Archor, the Eagle, and the Swan, until it goes beyond our view into Cepheus and Cassiopeia. . . The Milky Way is of much, greater importance than was realised until comparatively recent times. ■'Herschcl, by his star gauges, proved that'the number, of; fajnt stars in his telescopic field increased'l enormously 'as 'the central plane' of the '■' Milky,' Way .was approached. As methods of measuring stellar distances have been developed, it has been? found that the stars of our system extend.to.'.much- greater distances in the plane of; the-Milky Way than at right-angles to] it. llersuhel regarded.the system as an immense cloven disc... We now think; of it as a flat spiral.. 'Modern telescopes have re-, solved:a great part of the Milky Way intoiclpuds of stars, and it has been estimated that light would take 300,000 years to pass across the whole spiral. This great system, containing practically,: everything f-.wo • can sco without higk telescopic .powers',- is called the' Galaxy. But'just,as we have'found thatj our tooon is..but'; one of a'number of ■ satellites, our-.'e'a-rth but <a' single example, of, a ■ planp jnythc solar sys.tem,iand our sun^but one. of.thousands of millions of galactic stars, -so it is now believed that the galaxy itself is but one of a host of similar systems which form the portion of tho universe, which the telescopes of to-day are able to reveal. As we have taken the moon, the earth,:, and the sun as typical examples, each.;pf- tho class to which it belongs, so must .we. take the galaxy' as the type of the- spiral nebulae. "Everything,that ,-vve: know is in motion, eaehl.separntevbocly seems to spin as it:'flies; thro'iigh.'spaco. The satellites- spin-" oii'J theirr axes as " they whirl around" the 'planets^'tho planets

spin as thoy hurry round tho sun, tho sun spins as it speeds, we know not why, towards the constellation Lyra,; and the galaxy itself spins as it flics with terrific speed in its daneo with the other spirals. Eotation and revolution seem to bo characteristic of the dances of tho spheres, whose motions arc nioro closely related to those- of tho I waltz than to those of tho modern jazz. Tho galaxy, instead of being tho whole universe, as was at one time thought, is but our typical example of the kind of unit out of which the vis- I iblo universe is built. It is the greatest unit yet known to us.. "Wo cannot say whether the mighty telescopes of the future will disclose systems of a higher order built up of spiral nebulae. I But the'galaxy is so astounding in its extent' and sublimity that we cannot hope to form any adequate conception of it. It is difficult enough to picture the fiery grandeur of the sun, how then can wo imagine thousands of millions of suns, many enormously greater, hotter, and more dazzling than our own? Again, we find that many are double, othorsare grouped in brilliant families, and,'in a hundred cases, tens or hundreds of thousands of suns arc-' associated each in a globular, swarm. Many stars are variable in their brightness, and occasionally a nova flashes out, rising from, obscurity in. a few. days, or even in a few hour's, until it shines with 20,000 times the brilliance of our sun. From this acme of intensity it sinks again to obscurity in a few weeks or months. Nearly every one of these astounding outbursts-has taken place where stars are thickly; strewn in or on tho borders of .tho Milky Way, or in the-spiral nebulae. Bat we have seen that the galaxy is

not composed entirely,'.of stars. Some hazy-.patches defy resolution, into luminous points, and the spectroscope has proved that many .-of; these', are indeed clouds of luminous gas..; Those are the galactic nebulae. They are all' definitely associated with-, the Milky Way. So also are.the dark .' clouds of nonluminous matter '■ or'; cosmic, -.dust,1 and so are the much smaller 'gaseous ■ shells, surrounding hot stars, which'are called planetary nebulae. .- We showed last week a. photograph of a gaseous nebula which bears a, curious resemblance in shape to tho! continent of. North" America. ' To-day we show an enlargement of the southern end of 'this' nebula, which reveals, ■ still more clearly, its extraordinary'character. ' The photograph,. was taken by Professor,.'J. C. .Duncan' with the 101----inch reflector at' Mount Wilson on 26th July, 1922.' The exposure - was five hours.'1 The strange- intermingling of dark, and,, luminous clouds is very striking.- In places they seem \to be definitely .related to one ■ another, the darkest clouds having brilliant edges. The stars appear much more numerous in, the bright than in', the dark x portions. This seems ;to ' sliow that the nebula is nearer to;us than.most of the stars, and also that the dark portions are more opaque- than the light ones. According to Hubble's theory, this nebula is lighted up.'by the giant star Deneb ;or Alpha Cygni. _ This hardly seems credible. Deneb is about 3 degrees from the nebula, so, if the star is 650 light years from us, as stated in the Canadian handbook, it must be about 31 light years from the nebula. Deneb is .about ib;000 tinles■'.as'.bright as ■ the sun, or nearly 100 times as bright as Sirius, but it is ■ four times, as far from the nebula as Sirius is from us. Its light on the nebula, therefore, would be about six times as strong as that' of Sirius is here. That seems quite an inadequate illumination to reveal the marvels we see. There will be plenty of problems still awaiting solution- when the giant telescopes, planned by Professor Hale in. America and Professor Bitchey in France, are ready to reveal fresh mysteries in the- sky.