WONDERS OF THE HEAVENS

Otago Witness, Issue 3513, 12 July 1921, Page 19

WONDERS OF THE HEAVENS

MATHEMATICAL ASTRONOMY. X decidedly interesting evening was spent at the Museum on the sth inst., when Professor White delivered an address on the subject of astronomy in general and mathematical astronomy in particular. The address was delivered under the auspices of the Astronomical Branch of the Otago Institute, Mr R. Giikison (chairman) presiding- over a numerous attendance, which included a number of ladies. Professor White, who was received with warm applause, first of all gave a brief historical sketch of the science of astronomy, lie stated that in primitive times man hail leisure to study the stars, but as the demands of civilisation became more complex this oldest of sciences drifted somewhat into tiie background. The daily recurring phenomena of the heavens, so familiar to us, seen every day and night of our lives, were viewed with indifference, and it required the appearance of a comet and the threatened destruction of the earth to arouse any interest in astronomy. But there were other reasons for this lack of interest. Mathematical astronohiy was rightly regarded as a very difficult branch of. science, which only a few c-ould understand, but the subject hail a popular side as well, and that side well repaid any study that was devoted to it. It was not known who first mapped out the constellations or who first gave them their peculiar and picturesque names. Thev bore the same names to-day that they had 4000 or 5000 years ago. The Chaldeans. Babylonians, and Assyrians had left some authentic records of observations regarding the constellations, and some of tire more conspicuous stars; and by their association of the simultaneous appearance of the’Se stars with certain natural events it- was easy to understand that they should consider the stars as tho controlling forces in bringing about tnese physical changes, that indeed the stars ruler! tiie earth. The Egyptians sfcuclicd die stars more systematically, and jheir reappearances were used to fix tiie oeginnmg of the year and to determine then- religious and civil festivals. The t yramids of Egypt had been the subject of much speculations, and one curious circumstance to which he would like to call attention was that in the Great Pyramid taeie vva.s a passage directed at an aggie towarus the Pole Star and another passage on the souih-side directed to tiie Pleiades at its culmination at midnight at the vernal equinox. _ But it was to tiie Greeks that wo wore indebted for the fundamental principles of scientific astronomy. I’hev wore great mathematicians and they applied this knowledge to the study of the earth as well as to the motion of the heavenly bodies, llyparclus and l’tolemy were both great astronomers, but so long ns the Ptolemaic system held sway no further advance than that made by the Greeks was possible. MEASURING THE UNIVERSE. Coming to weighing- and measuring of the earth, Professor White described the various methods by which this had been done so as to attain results that would be scientifically accurate, and outlined the various considerations such as shape, volume, density, etc., that had to be taken into account. Proceeding, he described how the distances between the various heavenlybodies were measured and measured with an extraordinary degree of accuracy. lie first of ail explained what was meant by parallactic angle, or the apparent changes of

place which a body underwent by being viewed from different points. From this point he went on by means of diagrams detail how it had been ascertained that the moon was a little less than 240,050 miles distant from the earth, and that it had a diameter of 2160 miles, The mass of tiie earth was 80 times greater than that of the l-noon, and the density of the latter threefifthat of the earth. Speaking of tiie sun, he stated that, although to our eyes it did ! ot appear any larger than the moon, yet in reality its disc was 'OO times greater than that of the moon, the actual difference being due to the fact that it was 400 times further away. The sun was 866,000 miles in diameter, and v;e could place ICO of our .4-olies .side by side across its diameter, but even this comparison failed to give an adequate idea of its actual size. Tile volume of one sphere compared with another was represented by the cub: of their diamoteT. Measured in tills way, the moon would bo represented by the figure 8, the earth by , an< ! tbe sun by 1,305,000. The mass of the sun was to the mass of the earth as 330,000 to one, and was indeed much greater than that of all the planets put together. Calculated by parallax the distance of the sun from the earth was 92.908.0C0 miles, and other methods of calculation had given approximately the same result, showing, in the words of Professor Newoombe, the striking correctness of the astronomical views of the earth. Dealing with the movements of the planets the lecturer stated that the student was at once struck by the fact that the whole movement of the solar system was essentially a problem of mechanics and higher mathematics, and that certain well-defined lines of calculation gave results that would inevitably verify themselves. ISOLATION OF Ot R SYSTEM. “If one could see the solar system from the outside as it were, what a marvellous sight it would present,” continued Professor Vviiire. “Here are eight planets with attendant. satellites, differing in size, at unequal distances, revolving in the same direction in orbits more or less eccentric and with varying velocity, all rotating with their axesqat different angles to their planes and in the centre the great sun, vastly greater than all of them put together, holding thffui all in subjection to his power, j And is it not really wonderful, too, that j man claims to explain all this complicated ; movement and to say at any given moment | where they are to be found” and their relative positions? Having, thus mastered the problems of our solar system, the astronomer finds new fields of observation and study in the stellar worlds, and he shows us that our little solar system is completely separated from the rest of the universe, and is entirely isolated, so to speak, from the great, constellations in the heavens. I am neither an astronomer nor a mathematician, but, I am very interested in (he underlying principles of the science, and in a sense the astronomer holds the sun. moon, and stars in the hollow of his hand and weighs and measures them.”—(Loud applause.) Ihe Rev. D. Dutton moved a hearty vote of thanks to the lecturer for the able and lucid manner in which he had placed so many aspects of his large subject before his hearers. In seconding ihe motion Professor Jack also emphasised the accuracy of astronomical calculation, using as an illustration, the ease of Halle v’s comet, which had reappeared some years ago after an absence of 75 years. The point at which the comet • would reap; car was calculated and a teleI scope was directed towards that particular spot. A photograph was taken of the sky, and when the plate was developed an impression of the comet was found there. The speaker also described how an eminent American astronomer had recently ascertained that the diameter of the brightest star in Orion was one-four hundred thousandth that of the sun. This had been done by using mirrors 20ft in length to reflect the light, from this star on to the lens of his telescope. j Ihe motion was carried by hearty accla> | mation.