IN STARRY SKIES

Evening Post, Volume CXIV, Issue 92, 15 October 1932, Page 7

IN STARRY SKIES

CLUSTERS AND NEBULAE

HERSCHEL^ DISCOVERS 2500

(By "Omega Centaur!.")

The astronomical achievements of Sir William Herschel appear even more amazing when we- realise that half his long life had passed before he was able to devote anything more than his surplus energy to scientific research. He was indeed 34 when first he hired a small telescope, only, two inches in aperture. Naturally this proved quite unsuited for the serious work he wished to attempt. If he was to succeed ho soon found that he would have to construct his ■ own instruments. In two years.he was able to view the heavens through a much finer telescope made with his own hands. But it was astonishing that he could retain his enthusiasm during the long night wajcdies, after strenuous toil as a music teacher during the day. Under such circumstances we may well marvel at hisinitial determination to scrutinise and study the entire heavens as far as it was possible to view them 'from land. For eight years he continued this survey.under.great disadvantages, and in the course of. it made a marvellous [series.of far-reaching- discoveries. It was indeed fortunate, for science

that • one of these, the discovery of Uranus, aroused the, attention of the world and led a.year .-later, to his being, freed from „ the necessity of earning his daily bread. It .was in 1781, as we have seen, that, the planet, caught his eye, and in-1782 he was granted a salary of £200 a year as.the King's astronomer. Thus, at the age of -44 he was able, for the first time, to dovote his full energy to• .astronomical ( .research. In pursuance of his'tffiginal aim to discover the structure of the universe, he was ,now ablo to devote- more time to star, gauging,, adopting at different periods two, distinct methods. In the course of these researches he coufitcd the stars in:3400 fields and . compared them photometrically. With the object of. determining stellar, distances he paid particular 4 attention to \ pairs of stars that appeared, extremely close to one another in the sky, expecting to find,,that .the earth's, annual journey round the sun wo^uld niake.tne nearer star' change it/3 /apparent'position /with, respect, to the more distant one. Instead of this he', found' that the stars in many.pairs ,werfl.physically' connected

with one another revolving ronnd thoir common centre of gravity, and he made a catalogue of 806 double stars. It soon became'clear to him that the galaxy is not made up' exclusively of stars strewn indiscriminately in space. Great numbers of hazy spots of light, quite different from the sharp stellar points, attracted his attention. A few of these had long been known. Ptolemy mentioned six. Three of these are loose groups of stars which can be resolved even with the naked eye. The other three are Praesepe in Cancer, the double cluster in Perseus, and the bright cluster in the tail of the Scorpion. Omega Centauri, 47 Toucanae, and ono or two others are shown as stars in the maps of Bayer and Tlamsteed. The Great Nebula in Andromeda was noticed by Al Sufi in the tenth century. The Great Nebula in Orion was discovered with the help of a telescope- by Peiresc in 1610. But the first catalogue of such objects was not made until Herschel's time. Messier, the great ■ French comet-seeker,' regarded these really stupendous objects as obstacles in his search. As early as 1771 he drew up a list of 45 of them for his own guidance, and in 1781, the year in which Herschel discovered he published a catalogue of 103. These objects are still referred to by their numbers in this list with a capital M prefixed to indicate Messier, who examined all these "embarrassing objects" as he called them with a telescope only iwo feet long and 2} inches m aperture. Most appeared to him to be " nebulae/without stars,'' but more than half are- in reality globular clusters of stars. Of the others.some are planetary nebulae, some are gaseous

nebulae, ana some are . spirals. Since they were- all observed with such a small instrument they are magnificent objects seen through modern telescopes or depicted by celestial photography. They form a considerable portion of the objects illustrated iv astronomical books of all kinds.

Herschel went about the study in a far more systematic way. In 1786 he was able to- publish a catalogue of a thousand new clusters' and nebulae that he had discovered. Three years later he added another thousand, and in" 1802 .five hundred more. But what are these mafvellous objects? . Herschel found that many which appeared nebulous to Messier wereTclearly clusters of stars. As he made larger and larger instruments ho resolved more and more into stars. For a time he thought that if ho could make a sufficiently powerful instrument, every one would be'found to, bo composed of ■■ stars. If so they must be galaxies like the gigantic one of. which our sun is a humble member. With this idea Herschel is said once to have- remarked that he had discovered fifteen hundred universes. But when, in 1789, ho made his great fortyfoot telescope, with a mirror four feet in diameter, he saw that there were objects of several different lands. Many were glorious- clusters of many thousands of stars, . arranged like a swarm of bees before they settle. But others to his keen gaze appeared to consist of some shining fluid: The Great Nebula in Orion was an outstanding case, if this is composed of shining fluid,, as we now know to be the case, it must-be niuch neare© than he had previously supposed. It is indeed a member of our galaxy, not an independent cosmic system. Many other nebulae appeared to bo similar to it, and also composed of shining fluid The curious class of. planetary nebulae also/except for the central star, appeared mainly, gaseous, and if the bright central point is comparable with a single star they too must belong to our galactic system. Herschel, throughout his career, held his theories but lightly, modifying them as fresh evidence appeared. •In 1811 he announced that' his opinion as to the arrangement,of the s t ars had undergone gradual change. He ' was convinced that stars are- not uniformly scattered throughout the galaxy, but ,that in many places there are comparatively compressed clusters of stars. He became convinced also that his greatest telescope was' quite- unable to disclose the limits of the universe. The peat problem of his life he had to leave unsolved, but his researches had revealed a grandeur and sublimity that had never been suspected. He had laid a sure foundation ■ for the marvellous progress of the next hundred years. His son, Sir John Herschel, extended the work into the Southern Hemisphere. In the catalogue of 5000 nebulae and clusters published in 1864 all but 450 were discovered; by the Herschels. In that same year' Sir William Huggius examined the spectrum of a bright nebula and.confirmed Sir William Herschel's opinion that it is not an aggregation of stars, but that it is composed of luminous gas. Modern research has shown that Sir William Herschel's early and later opinions " were both partly ;right. i The gaseous nebulae, both planetfary and diffused, are members of our galaxy. The star clusters also appear to be associated with it, but the spirals are external cosmic systems.