ROTARY CLUB LUNCHEON

Wanganui Chronicle, Volume LXXXI, Issue 19050, 1 July 1924, Page 2

ROTARY CLUB LUNCHEON

THE ORBS AROUND US. ADDRESS BY MR. J. T. WARD. At the weekly luncheon of the Rotary Club yesterday, Mr. J. T. Ward gave a lecture on recent telescopic achievements. Mr. Ward, in his opening remarks, referred to work done iu the last 24 years. The older astronomy dealt almost entirely with the positions of celestial objects; the more recent work had to do with the nature of those bodies. What might be termed physical astronomy had to do with the investigation of the size, temperatures, and evolutionary phases of the different bodies of the universe. For this purpose telescopes of great aperture were required. The visual work was still essential, but all the more important and lasting work was now registered by photographic plate.

“This sets no limit to the size of the telescope,’ l said Mr. Ward. “All light from the stars comes in parallel rays, and it is the purpose of the great telescope to collect as much as possible, so that distant and faint objects may still form an image sufficiently luminous for investigation. Much of our important knowledge has come through the spectroscope attached to the telescope. This instrument disperses the light, and it is necessary that we have

plenty when it Peonies to investigating the properties of faint stellar objects. By means of this arrangement of telespectroscope we are enabled to tell at what speed an object is moving in the line of sight. We are enabled to measure correctly the rotational speed of the sun ou its axis by taking the light, which poaches us from the side of the sun, when it is turning towards us. In like manner we may measure the light from a star that is moving directly towards us, or receding from us. The condition in which the different stars happen to be at the time of observation is made clear to us through this instrument. It informs us of the different chemical elements which go to make up the sun, stars, or those cloudy structures known as stars or nebulae. The classification of the stars would be impossible without this instrument. Prior to the opening years of this century, the idea that prevailed was that the white stars were at the beginning of the scale of stellar development, that the yellow stars came next. Then followed the red, and the redder the star the older and cooler it was. Today, through the closer investigation made in our time, we find the star begins as a loosely compacted mass of material of enormous volume, and low temperature. It shines with a dull red glow. In this stage these stars are known as red giants. In processes of development the temperature rises, and the colours change from a deep red, ’ through orange and yellow, to a brilliant white, and, in the hottest starts of all, to a distinct bluish white tine. Only stars possessed of great mass or substance ever attain to the bluish white state of stellar evolution. The process appears to come about through shrinking and chemical change. Professor Kussell puts things somewhat in this way: Stars leak heat, and the more they leak the hotter they get. This sounds paradoxical, but is nevertheless true. Arrested motion turns to heat, as the stone which is dropped on the pavement or the bullet which is fired at the target. After the star has reached its zenith, which it will do as Jong as it continues to contract, it will then begin to cool, and will then pass through all the stages, developing the different colours, again in the inverse order to its rise, finishing as a visible star of a deep-red tint, a much-reduced temperature and a small dense volume. In this reduced stage the opposite of the former, the star is known as a dwarf. This knowledge of the processes through which stars pass in their development enable us to investigate the fainter and more distant objects in the universe, whicl before the coming of the great telescope were a sealed book to us. In the investigation of certain classes of stars, ■ one of the most important discoveries ever made appears to have given us a means of measuring the distance of some of the most remote objects in the universe. This came about through a study of certain stars, the light of which underwent very rapid changes. The brilliancy of these stars was found to diminish and rise again to original brilliancy in a period of less than twenty-four hours. The first notable example of this class was found \in the constellation of Cepheus, since I when many others have been found. All this class have been termed Cepheids. Any star of this type was found to be a body having about one hundred times the brilliancy of the sun, and possessed of considerable mass. A number of these, whose disj lances were pretty accurately known, > were found to Jpive a certain fixed reflation between , their absolute magnitude, and their period of variability. i This fact became a key by which the astronomer proceeded to unlock the problems of great star clusters in distant parts of the universe. Absolute magnitude signifies in astronomy what candle-power does to the electrician. It means the amount of light sent out

by a star at a certain standard dist- ■ ancc. This determination goes a very 1 long way to inform us of the distances 3 of the stars. If we know the particu- ‘ Jar class of star, and its absolute mag- c nitude, and we compare it with its ap- 3 parent magnitude, then the difference c will afford us a very good guide to its 3 distance. In this way sonic of those 3 close clusters of stars known as globu- £ Jar. have been very fully investigated. ( From seventy to a hundred of these j objects are known. Two very fine; examples are visible in our southern J skies, one near the Cross, another dose , to the smaller Magellan Cloud. Those - are considered the nearest of these Ho- j jects. There distances are such jhat . light moving at the rate of 184/100 miles per second, or about six billon 3 miles per year, takes no less than 22/;jo J years to reach us. The farthest obje-f s * of this class knowi? until recently w£s ! 4 over 200,000 light-years distant. Nov, ] in the last few weeks, we are informed ] that Dr. Harlow Shapley, of Harvar: j College Observatory, U.S.A., who ha. • done so much in this particular line oi J investigation, has just been determining the size and distance of one of ’ these clusters, which he places at the astounding distance of 1.000,000 light* years. Some of these globular star clusters are found to contain many thousands of stars. Each one would j be separated from the other by as great a distance as our sun is from the nearest star, or a distance of from twenty to thirty billions of miles. Light would take nearly 500 years to pass from one side of such a cluster to the ether, yet to the naked eye of man, looking out

1 into the universe, one of these Stupendous objects appears as a faini point of light. Mr. Ward gave a detailed description of the instrument recently Iwought into use at Mt. Wilson Observatory, in Southern California. This is Shown as the interferometer. He added® “By a skilful arrangement of reflecting.,mirrors standing out from the telescope, and reflecting the light into thfigiube, we get the effect of a telescope ME feet in diameter. One is now beindjfeconstructed which will give an equaHHent of a telescope 50 feet in diamete®Several stars estimated to be of gr«Ssize have been measured with this mfetrument. Three may be mentionedl/They are in the class known as super-mants. The stars are Arcturus, in Bootes, Betelgeuse in Orion, and Anta®s, in the Scorpion. The first is fourfe. to have a diameter of twenty-one iHillion miles, the second a diameter of 2115 million miles, and Antares, the greatest star so far known, has the onolrmous diameter of 400 millions of. .miles. Some idea of the difficulty of making such measures may be gathered fj/om the fact that to measure the diameter of a star like Sirius, an instrument' offi at least 100 feet would be required. .? From these and additional makers furnished by the speaker was formed a com option of the immensity of spica, , tnd the enormous dimensions of mShy * f the bodies contained therein. | • ' After the conclusion of his addr| Sß -\r. Ward was accorded a hearty v*te ; c thanks.