IN STARRY SKIES

Evening Post, Volume CXII, Issue 81, 2 October 1931, Page 14

IN STARRY SKIES

■;.(■■ CELESTIAL COMPANIONSHIP

{By ' 'Omega Centauri.'')

!y ilu the heavens, as on earth, it is not iwelTto bo alone. Amongst celestial "botlies and systems of every kind we ■jfind" enduring companionships. We go "out on'a dark clear night and soon see ;a "streak of light flash across the sky. 'A tiny meteor has met its end by rushing; headlong into tho atmosphere. We think of its long solitary journey, through the cold void of space, which has ended so suddenly and so brilliantly,. It seems to be, until it met tho "earth, a picture of utter isolation. But attentive observers find that numbers of similar streaks of light appear to diverse from1 a single point. The meteors, though far apart, are not absolutely alono. Numbers of thorn aro pursuing parallel paths, and.aro apparently en-. Joying somo sort of companionship. Occasionally, we see a more arresting sight. A brilliant comet comes to pay its brief obeisance to the sun. It is not a single body, but a vast assemblage of meteoric masses travelling in company. Sometimes such an association which has endured for ages 'is broken up during one of these visits. The fragments which come closest _to the suii are more greatly swayed by its lupenor attraction and are drawn

tewaysfrom the rest of the swarm. But even/ when: separated ;by .millions .of iriiles, they still show their relationship Vyi. travelling in similar paths ; around thesun..- ' '.'. '..:-. " ' '•.■.,

Passing.to larger bodies : wefind the earth accompanied in fl.ll its wanderingsl by jta faithful attendant the moon. TJie two dance (BloWJy" at they fly Along' their annual jpurney. To us the moon seems to be for ever describing roiirid the -earth, but seen from "a distance its track around the ■un is a smooth curve. For while. it , aways from one side.of: the earth to the ©tfier,''. a 1 distance, of less than half a ttUlipn'.niiles, it. rushes with'the earth about i forty-five million miles along its iprbit.-:■■. ,■■ -. ' • .''■; ■■■'' ■; ■ . -Thei ■■ great '■■ planfets, Jupiter and Baturn,: have large families'of satellites,' ,Uranus" has. v f our. and ' Neptune', . one/ whilst little. Mars has Wo tiny':attendants. Pluto;may bo lonely' an^. out in the icoid, but-Mercury uand,-. Venus, though'without the moons, are near the: ■uri) and. the planetoids form a gigantic failiilyv of .dwarfs. The istars look to, us ' io ; .be independent points of ■.light,: but, jrhlen :they are examined with'the tele-" •cope \andl spectroscope, ■ one "• in 'every thTee.or' four is found to have<a mass : ive'compknion, and probably very many tit those- that seem alone 'have families as numerous-as that of the sun. But 'ihisjis notuall. Besides forming-pairs-and. small groups, stars form much greater., associations, star clusters containing thousands or hundreds of thouands of suns, and star-clouds containing millions. .•'•...■'.,'..: •'.'■• j; Then the vast galaxy itself;is .an ■BSociation of stars, clusters, "clouds, and!nebulae. • , -'.■ '■'-•,."■, ■■'■■_'■•:

■ But far away beyond- the .utmost Ibounclaries of the galaxy," mostly at flist'ances; that light takes/.millions/: of

Jjreafs io 'cross, lie hosts of { glorious Bpirals. And even here we find - a Similar tendency to form: associations. Jlhe- into two* vast groups, one north, the other south 'of the galaxy, tis - probably illusory. But aebulao seem, as eager to form.partnerships aa stars. "VVeMiaveshown .seiv^ra.l photographs of pairs of spirals, and in ; *' .■. ' ■ '■■."'■ :■ -.

ono ease tho two seem to bo actually meeting. The galaxy is accompanied by tho two smaller systems called tho Magellanic Cloutls, and this type of relationship appears to bo not uncommon. Tho celebrated Whirlpool nebula, Msl, the first found to bo a spiral, has a marvellous glowing mass at tho end of ono of its arms. But tho best example of quasi-Magellanic companions is furnished by tho Great Nebula in Andromeda. Wo have already shown two photographs of this, but to-day we give an enlargement of tho central part. This picture does not give tho two attendant nebulae, but they are well shown in each of tho previous ones, and they seem to bear jusft.the same relation to tho main nebula that the Magellan Clouds do to the galaxy. Tho photograph now shown was taken by Professor G. W. Bitchey on 13th October, 1909, .witji tho 60-inch reflector at Mount Wilson. The exposure was twO hours on a Seed 23 plate. This gives a good idea of the stupendous nature of these cosmic systems which aro now being studied by the million. It is one of tho very nearest of tho spirals to us, and yet it is impossible to form any clear conception of its distance. We know that light, which could go seven times round tho world in a second, takes about eight minutes to come from the sun, and four years and four months to come from Alpha Centauri. It is hard enough to picture such-a distance as the latter, but how can we realise that' tho light which impressed this image on the photographic plate had been speeding from the nebula to us at the rate of a wireless message for j 930,000 years. And nebulae can be de-i

tected with the hundred-inch' telescope 'which are 150 times as far away as this one. Even to cross from one side of thift nebula to the other, light would take' 50,000 years. The diameters of the two attendants, which with moderate powers lopk like stars, are 10Q0 and 2700 ljght years in length. The nebula is as bright as 63Q million suns.

• It is amongst systems of ; such-' •an astounding scale of magnitude that we next find the associative tendency; "We have seen photographs of pairs and of a- few small groups, but, now that bo many more nebulae are within the reach of observation, it is clear that there is a strong tendency to form'much large? assemblages, Already'a hundred or more distinct gatherings, have been recognised, i many 'oi which contain more than a score of separate nebulae; We have spoken of .the, Cpma-yirgo .region where, the density of, distribution exceeds ' eight: times the ' average..!; • This cloud of small;galaxies is estimated to bo ten million light years: away, and tvfOJ million .'light; years in . -diameter. Most 'o'f.rtho other known groups; of nebulae, such; as f that in Pegasus,; of which^we had a glimpse last week, are distinctly smaller. But many are at such distances, 100 to 150 million■; light years, that they, liave npt .yet been investigated/ and some of these may surpass the Coma-Virgo group. -Thisisthe limit at present imposed' by telescopic powers. But it is clear that up to the highest order of systems yet-known the formation of associations is- the rule. Shapley regards the galaxy)as au;exaniple of thb survival of the mPst massive,; and considers it more like one of these;groups of nebulae than, a single Bpiral. It is pleasant to find from; his new book oh Star Clusters that he does not adopt the dismal doctrine of Joans that the universe .is ..running down or radiating itself away. \He is more willing to assume ,the essential permanency of the arrangenicnt that is now observed, and to deny that stellar development is undireetional. Stars and system may move up the luminosity s.equencei as well as down, and towards gigantisiii as well as toiyards minuteness'of mass. ' : . ' . i