IN STARRY SKIES

Evening Post, Volume CXII, Issue 87, 9 October 1931, Page 14

IN STARRY SKIES

SHAPLEY'S RECENT

RESEARCHES

(By "Omega Centauri." )

1 The great problem of astronomy must (Tver be to find out tho nature of tho Marvellous universe by which we are surrounded, and to dotermine our rolation to it. This was ever tho aim of Sir William Herschol, and now Dr. Harlow Shaploy, director of Harvard Observatory, is attacking tho same problem with far greater prospects of success. Hersehel had to make his own instruments, he and his sister worked alone, and ho had to rely entirely on visual observations. It is a century gnd a-half since he discovered Uranus. Astonishing progress has been made since .that day, but we are still studying the problems which filled his thoughts during all the rest of his life. Hersehel very soon showed that the effects of gravitation can be detected in distant space. In many double stars the components were found by him to be revolving about ono another. Then he discovered that the sun, attended by all its planets, is in rapid motion through space, and ho determined to ■ound the depths of tho Milky Way as far as his instruments would allow. He *oon realised tho need of greater light gathering power, and his labours of telescope construction culminated in the

teompletion of a reflector 40 feet in *<>cal length, and four feet in aperture. At one time ho thought that with this lie had pierced through tho Milky Way to; its very' boundary, but ultimately he concluded that the galaxy was fathomless with the telescopic powers tiat he had at his disposal. We have geen.that he was tho. first to,suggest that Some of tho nebulae that ho discovered are external, cosmic systems. t?6, although he could not see the faintest stars of our galactic system he actually discovered objects ever so much farther away, and gained a conception of the sublime grandeur of the universe, such as no . man bef oro him iad ever dreamt of. ■ The worker in the same fields to-day is. very differently equipped. He has for his guidance, all the additional data that aave been accumulated during the last 150 years. The power of Mb instruments, has been increased more than fourfold, and their quality has been immensely improved. But this is not all. Entirely new methods Jiave been invented, and accessories of all kinds multiplied. The most profound changes are due to photography and the spectroscope. Visual observation! are becoming less and less important. Most researches ' depend on: the photographic plate. In the collection at Harvard there are hundreds of thousands of original photographs. Other observatories are storing, up records in a similar way. From an examination of these plates and a comparison of one with another most astronomical discoveries are now made. In one special research on variable stars thousands of plates have been taken; by Harvard Observatory during the last few years. On these two. or three thousand new variables have been found, and it is expected that in a few years tenor .twenty thousand, more will be added to the list. This is specially important because- certain types "of variables act as. "standard candles" in the universe, enabling distances to be measured that would otherwise bo absolutely, out of reach. Binary stars are revealed, moro often.by. the.spectroscope. Double stars are known by tens pi thousands, but Shaploy estimated that there aro undiscovered- millions of them amongst the stars that have been photographed. But per•haps the greatest work of photography •in astronomy has-been done in reveal-

ing the existoneo and structuro of star clouds and nebulae.

Two important books by Dr. Shapley wore published last year: One is on "Star Clusters," and the other on "Flights from Chaos." In these ho gives the latest pictures of the probable relation of our solar system to the galaxy and of the galaxy to the rest of the visible universe. Every now discovery seems to emphasiso more strongly the vastness of the latter and the comparative insignificance of tho sun amongst tho hosts of heaven. The Milky Way on the other hand grows in importance. Hcrschol's idea that some nobulae are external cosmic systems has been amply proved. To an observer on a planet of a sun well within one of the spirals, the star clouds of tho nucleus and the arms would form a band of light liko our Milky Way. But Shapley challenges the belief that our galaxy is no more than a single ono of the millions of spirals. The usual nomenclature is rather puzzling. Names were given when the true nature of the objects was unknown. As long as the galaxy comprised everything known to exist, it was appropriately called the Universe. But tho title f Island Universes" applied for a time to the spirals, was a contradiction in terms. Was not tho prefix "Island" also inappropriate! Is the Milky Way any greater than ono of the Spirals? For a timo it was believed to owe its apparent overwhelming importance to • the fact that it is close to us, and we view it from within. But recont measurements seem to show that it is really great in comparison with the average spiral. But tho external systems are not all spiral in form. Three or four

per cent, appear to bo of an irregular type, so there must be thirty or, forty thousand systems like the Magellanic Clouds within tho roach of existing telescopes, What should they bo called? Shapley applies tho term "Galaxies" to thorn and to the Spirals, restricting the term nebulae to tho masses of gas or dust that form luminous or obscure patches in our own system, in the Magellanic Clouds, or in the Spiral or irregular external systems. This makes it unsatisfactory to use the term galaxy, as we have been accustomed to do, as an alternative to "Milky Way." In Shapley's latest classification our galactic system, as it used to be called, is two orders above tho typical galaxy ' snehas one of the Magellanie Clouds or i. one ,of the spirals. Between the two we have double or multiple systems of galaxies. We give 1 to-day a. photograph of one of these, a group in Pegasus. The photograph was taken with the 60-inch telescope at Mount Wilson on 26th and 37th August, 1916, with an exposure of 7 hours 45 minutes. This Shapley considers to be a flattened group, as threo or four of its members appear to have nearly parallel galactic planes. He recognises a.marked tendency for galaxies to assemble gravitationally, and considers this to be a collisional group. One of the spirals appears binuelear, and an arm seems to be broken off. In the original photograph there are many faint, and probably much more distant, systems, that are lost in the reproduction. An observer in ono of the members of tho principal group would see ; motions such as we. recognise as star ■ streaming arid galactic rotation. But ; even such a group of galaxies as this i is believed to be far smaller,than our . Milky Way. The latter bears to a single spiral •a' relation somewhat . similar to that of a_ small star cluster ■to a single star. Systems such as our ' Milky Way. and the great group of 1 systems in Coma and Virgo are classified by Shapely- as; super-galaxies. He is i inclined to recognise tho system that i' bemused to.call the local cluster,: mark- ■ ed:.by .Gould's belt ..of_bright.stars, as : having a status approaching or pos- '. .sibly. equalling that of a spiral. This i system may ■bo in contact with the1 !' star cloud of Cygnus, but seems to bo ■ well separated from the. great star ' clouds of Sagittarius that form the ■ nucleus of tho super-galaxy.