IN STARRY SKIES

Evening Post, Volume CXIV, Issue 122, 19 November 1932, Page 7

IN STARRY SKIES

THE SUN'S PLACE |N THE UNIVERSE

(By" Omega Centauri.")

The sun's great family of planets, satellites, asteroids, . comets, and meteors extends over a space that is almost inconceivably vast even in these days of: war debts and unemployment, when everyone. is forced ,to think in millions. The sun itself is an immense body, more than 1,300,000 times the volume-of the earth, and its distance from us, nearly 93 million miles, seemed a good long unit until man began to explore, the. galaxy and still more distant systems. Pluto, the most. distant planet known, sails majestically round its. long orbit in about two and a half centuries,' sweeping out an area 1600 time's as great as the orbit of the earth. Buti the whole, solar system is but a speck in; one the minor star clouds of the galaxy, and the galaxy itself is but one of a host of systems the number of which is absolutely unknown. The solar'system is_ astonishingly isolated; in! fepaee. It is: easier to-picture this isolation if :we make a- model. Let us; represent: the sun by a. marble an inch-.in diameter. Thus the giant Jupiter will be represented by a mustard seed,;and,; the-other- planets by grains of sand.' All.tHe..model's, except that of the sun itself, would not nearly fill a saltspoori. Let us_ lay them out in their proper positions in' the Basin Eeserve. The grain-of sand that stands for the carth1 will be three yards, and the mustard seed that Jupiter fifteen yards from'.the'model of; the sun. -The invisible: speck,:-that' stands . for Pluto will.be'.l2o :yarfls: away. ;On the same

scale : ;the nearest stars -will lie similar marbles, at. Cape Maria Van Diemen and. the'Blhff.respectively./ So this part of space -dqesi-not seem to be overcrowded. But a long exposure photograph of any part of tho sky sbows thousands of stars' whose images seem almost to touch' one another.- The 100-----inch • telescope.at^Mount, Wilson is said to -reveal one .or '■ two thousand million stars in our galaxy, alone.' In the reg-ions-near us it. shows small stars as well ;as^ large ones. In the more distant parts only the more.brilliant bodies can be detected., The. total number of stars in'the is probably at. least forty.tini'es as great as the number of those .that can1 be seen.: And this" estimate does:. not take into -account the possible, existence of thousands of mil-liouis.-of'.darlc' stars, as well, of course, as countl,ess, hosts of planets, satellites, and comets. We cannot seb-a"planet of any star ''except the '.sun, but wecannot thinkthat our sun is unique iii possess-ing-a-wpnderful -f £mily[ ■ But a; glance at the, heavens on any! clear moonless night' shows at once ■ that there is some--thing remarkable abpitt' stellar distribution. .A' glorious band ,of light spans the sky. \Ve call it; tho Milky Way. ! Explorations ' with giant' instruments have, shown.-thdt not only are' stars far more .'numerous along this .band than in other: parts of the 'sky,' but; that they l aic.,strewn: to' faT: greater ' distances.' The galaxy-is thus; found to be' a vast flattened assembly .of stars, 'at' least tens of thousands; of milliohs; in dumber,and 'spread to distances that' are inconceivable," although.'expressed now; with some ] confidence 'in' terms' of such units as the .parsec, Or the light year. The stars,-.moreover, .are suns, and when' we realise .what an' immense body onr sun is, aiid'with1 what' a terrific stove of energy ,it is. endowed, it is rather startling to'think'that- astronomically it is

a dwarf. Many stars are much fainter than, it. is, but there are countless others beside any one of which the" sun would sink into insignificance. . A typical Cepheid variable, for example, with aperiod of 100 days is normally about 20,000 times as brilliant as "the sun, and several other types of giant stars are,known. Every increase in telescopic power discloses fresh marv.els in the heavens,, and throws a'flood of new light on the greatest problem of astronomy, that of the structure and evolution of the universe.' One great difficulty is duo to the fact that wo view the Galaxy from within., There is no possibility of getting an outside view. Hence there is still considerable difference of opinion as to its true form. AH agree that it has a flattened structure, extending many times as far in the plane of tho Milky "Way as in the directions at rightangles to it. The great question is whether it is one vast spiral or a family of more or less separate systems. The status of the nebulae, long in doubt; has been definitely .settled. The irregur lar gaseous nebulae are within tho Galaxy, but the spiral, the elliptical, and the globular nebulae are all external systems. It is in suggesting the distances of some of these that the Cepheid variables have been so useful. PhotograpTis, many of" which have been reproduced in these columns, show that some of the nearer spirals are exactly like the Milky Way. A portion of the Great Nebula in. Andromeda, for instance, has .been enlarged, to seventy times the, linear scale, and then placed beside a photograph of ■ a.portion of a galactic star cloud: such; :a's due of those in Scutum ■• or Sagittarius. The two photographs are then iiidistinguish: able in' character; • This 'astonishing similarity suggests that'our. Galaxy is itself i a spiral. similar'tb one of these distant nebulae.. But, .as . far as is known.at present,', there .is one'"-great difference between our Galaxy and the particular nebulae -whose distances from, us are known. .Our sun. we have

seen is .a dwarf,, star, but-.our Galaxyappears to beagiant nebula. Its diameter.-; appears to be' five •or -sis times as great as that of 'the. Great Nebula in Andromeda. Associated with- our Galaxy there are : about a-hundred globular, clusters of star, such as Omega Centauri^47 Toiicanae, and Ml 3in Hercules. The.distances of many of these have been', determined. They form a flattened or lenticular group with a diameter of about 200,000 light years,-which'corresponda well with the estimate of the; size of the Galaxy. The great spiral'in Andromeda 'appears to have -a diameter"' of .only thirty or f6rty;thousandlight years: But since stars differ; enormously in size, there docs .not seem any reason why spirals shoiild.ndt d,o .tlie same,- and 'Professor G. W. Eitclien thinks mauy just visible .in the greatest telescopes, may be giant galaxies. M. ;Lucien -Rud'aux, who ■ has taken • many beautiful photographs •of the^ Milky Way witih • a lens only one and one-tnir.4-ineh.es in. diameter, has suggested that ;iristead of being a single spiral the;' Galaxy may.be a'family of a number of. separate spirals.- He has indicated possible; positions for these in-a diagram-here reproduced, which is taken from- ■ the;-''lllu'stra'ted -London News." Going;counter-clockwise from the top right-hand; corner, these represent . the star clouds in 1 Sagittarius, Scutum, Ophiuehus, 'Aguila, Cygnus,*Cassiopeia, Perseus, and Auriga. The , difficulty: is •' that this theory requires all these .spirals to be- approximately in a isingle> plane.' The -flattening- of .a single spiral: is easily- accounted .for by the encounter of two previously, existiing nebulae. Bjit'it'is ;difficult. to see any-ieason for aTI these separate spirals lying in a single plane. The star clouds are more easily-accounted for if they are considered ;to be knots'in the arms of a single-gigantic spiral.