OTAGO INSTITUTE.

Otago Daily Times, Issue 19550, 5 August 1925, Page 10

OTAGO INSTITUTE.

ASTRONOMICAL BRANCH. LECTURE BT THE REV. D. DUTTON. A meeting of the astronomical branch of the Otago Institute was held in the Museum last night. There were about two dozen people present, and the chair was occupied by Professor White. The lecturer for the evening was the Rev. D. Dutton, E.R.A.S., whose subject was “The Depths of the Universe,” based on the researches of Dr Hale at tho Mount Wilson Observatory. The Chairman referred to tho absence of Mr Begg, the secretary of the branch, who had left on a visit to the Old Country, anl who had been a tower of strength to them. Mr Begg had hoped to have an astronomical display at the Exhibition, but had found that to be impossible. The speaker went on to urge that those who could get possession of astronomical instruments should send them along for display at the Exhibition. Mr Dutton said that Mount Wilson was probably the most up-to-date of all the great observatories. Professor Halo was one of the outstanding men in the modern annals of the astronomical world. He had to his credit the invention of appliances and methods that had greatly facilitated the study of solar and stellar physics. For some time he was in charge of the Yerkes Observatory, where he had the use of the 40in refractor telescope, the largest of its kind in existence. Later he transferred to the Mount Wilson Observatory, which was connected with the Carnegie Institution of Washington, where were the great lOOin reflector, also a 60in reflector, and a collection of the most up-to-date spectroscopic and photographic appliances, and many other modern aids to research in the higher branches of observational astronomy. A great variety of work was carried on in this great astronomical workshop by a large company of experts and their trained assistants. Just as it was the man behind the gun that was the important factor in the gun's effectiveness, so it was with these wonderful instruments of astronomical research. The seeing eyes and calculating brains of these experts, seeing what they saw, calculating and expounding the results of their observations, and by their rational deductions, had given the world to-day literally new heavens. In their expositions, some of them, doubtless with an inevitable measure of the theoretical, were for the most part based upon the most convincing evidence. For stargazing the human eye was limited in its range *t> stars of the sixth magnitude. To the most long-sighted not more than between six and seven thousand stars were visible in the whole heavens. This did not mean that anyone from a given point of view could see this number, for not on the clearest starlight night could one see more than between two and three thousands with, the naked eye, and many persons had eyes too naked to see as many. With the advent of Galileo’s telescope in 1610 the number of the stars visible was greatly increased, for though his telescope was only a two and a-quarter inch im diameter it revealed stars down to the tenth magnitude of which they were known to be nearly half a million. Stellar astronomy made little or no advance until Sir Wilr liam Hershel at. the end of the 18th century set himself to the study of the stars and the structure of the stellar universe. For this purpose he used an 18in reflecting telescope which greatly increased human knowledge of the depth of the universe revealing stars down to the 15th magnitude, counting for all magnitudes then known in both hemispheres between five and six million stars. With tho construction of the modern giant telescopes so vastly superior in every way to the telescopes of Herschel’s, Lord Ross’s, and other instruments our knowledge of the depths of the universe had gone forward with great rapidity. The Mount Wilson 60in reflector penetrated to the depths of space where stars of the ISth magnitude congregated, and was capable of showing of all magnitudes in the heavens down to the 18th magnitude about one billion stars, while the lOOin diameter telescope added about five hundred millions more. The attempt to discover the distance of the stars was a problem that Hershel could not solve. While the gain of a magnitude in the penetrative power of the telescope revealed many additional stars, yet after a certain ascending scale in the number of (he stars as the magnitude decreased there was a limit to this ascending scale. Stars of the second magnitude were 3.4 times more numerous than those of the first magnitude, those of the eighth were three times as numerous as those of the seventh, while the sixteenth magnitude stars were only 1.7 as numerous as those of the fifteenth. The thinning out of these stars in a steadily decreasing ratio was probably due to an actual thinning out of these stars towards the boundaries of the stellar universe as the most exhaustive tests had failed to give any evidence of absorption o! light in its passage through space. In the new methods of determining the distance of the stars very successful work was being done at the Mount Wilson Observatory. Prior to the nineteenth century no measurement of a star’s distance could be obtained, but eventually by trigonometric parallaxes and using the diameter of the earth’s orbit as a base line 186,000,000 miles the parallax of star 61 Cygni was obtained by Bessel in 1838. Its displacement when observed from opposite ends of the earth’s orbit was found to be fourtenths of a second of arc—the diameter of a lin ball at a distance of eight miles giving the distance of 61 Cygni at about 40 trillions of miles, and as this was one of tho nearest stars to the earth it conveyed just a hint of tho enormous magnitude of the stellar universe. By trigonometric methods the distance of a few of the nearest stars had been measured. Now, however, by now methods used at Mount Wilson, tho number of stars which had known distances had been greatly increased. The spectroscope and an instrument called the interferometer in conjunction with tho 100-in telescope, were specially used in determining star measurements and distances. Standing on this small planet we were in touch with a star, the sun, the like of which there were millions in the depths of the universe. Our little world with its 8000 miles diameter, controlled by a star, 93 millions of miles away from us, having a diameter 865,540, sending its radiant beams to us, travelling at the rate of 186,000 miles per second, in about eight minutes, was part of a universe that stretched but almost to infinity filled with innumerable suns and systems. The area measured seemed so large that it made our sun a mere pigmy. Let them think of Belelgeuse with an estimated diameter of 215,000,000 of miles, and the mightier Antares with a 400 millions of miles diameter, and also of our 93 millions of miles from the sun taking light eight minutes to come from the sun to us and compare this with those giant suns that were so far removed from us that were our sun placed at the same distance he would scarcely be seen. Only four stars were known to be less than 10 light years from us. From the great star cluster in Hercules the light reached us in 36,000 years. These figures simply staggered the imagination, fight, travelling nearly six million million miles per year, took 36,000 years to reach here. To give an idea of the space-penetrating power of the great telescopes the lecturer handed round to his audience a number of photographs which showed stars of varying magnitudes. The lecturer said our solar system was very insignificant when compared with some of the great suns. The presence of these great suns lent some credence to what was called the nebular theory. There was a time when it was held that the solar system was a nebulous mass. Some of the giant suns would fill the solar system, but if there wag anything in the nebular system some of tho mass had been thrown off. The sun was a very heavy body as compared with some of the great stars, and was therefore further along its journey. The temperature of the great suns was low when they were diffuse, but when they became contracted they became hotter. Eventually the contraction reached its limit and tho process of cooling became so rapid that the sun became dark. Our moon must have been terribly hot at one time. Astronomical science was making remarkable strides and never was the advance more rapid than it is to-day. Mr Dutton was rewarded with hearty applause as he resumed his seat, and on the? motion of Mr G. Hoffman, he was accorded a very hearty vote of thanks.