MATHEMATICAL ASTRONOMY

Evening Star, Issue 17706, 6 July 1921, Page 8

MATHEMATICAL ASTRONOMY

AN INTERESTING ADDRESS,

ISOLATION OF OUR SYSTEM.

Under the auspices of the Astronomical branch of the Otago Institute IroiMsor White delivocd an interesting. address last evening on astronomy, and in pailioular mathematical astronomy.. ProiVuw While, said that it was not known who that mapped out the constellations, or who first g ive Ihetn then peculiar and nieluiesqne names. They Imre t-he same names to-day that they had 4,000 or 5,0C0 years ago. The Chaldeans, Babylonians, and Assyrians had left some authentic i ccords of observations icgaiding the constellations and some o£ tho rnoio conspicuous stars; and by their association of the simultaneous appearance of these stars with certa ri natural events it was easy to understand that they should consider the stars as the controlling forces in bringing about those physical changes that, indeed, the stars ruled the earth. The Egvptians studied the Mars more systematically, and their,_ reappearances were used to fix the beginning ol the year and to determine religious and civil festivals. The Pyramids of Egypt had been the subject of much speculation, and one curious circumstance to which he would like to call attention was that in tho Great Pyramid there was a passage directed at an angle towards the Pole Star and another passage on the south side directed to the Pleiades at its culmination at midnight at the vernal equinox. But it was to tho Greeks that wc were indebted for tho fundamental principles of scientific astronomy. They were great mathematicians, and they applied this knowledge to tho study d the earth as well as to the motion of the heavenly bodies. Hyparclus and Ptolemy were both great astronomer's, but so long as the Ptolemaic system held sway no further advance than that made by the Greeks was possible. The Professor described how the distances between the various heavenly bodies were measured, and measured with an extraordinary degree of accuracy. He first of all explained what was meant by parallactic angle, or the apparent changes of plaee which a body underwent by being viewed from different points. From this point he went on by means of diagrams to detail how it had been ascertained that the moon was a little less than 240,000 miles distant from the earth, and that it had a diameter of 2,160 miles. The mass of the earth was eighty times greater than that of tho moon, ami the. density of the latter three-fifths that of the earth. Speaking of the sun, he stated that, although to our eyes it did not appear any larger than the moon, yet in reality its disc was 4CO 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 856,000 miles in diameter, and wo could place 100 of our globes side by side across its diameter ( but even this comparison failed to an adequate idea of its actual size. The volume of one sphere compared with another was represented by the cube of their diameter. Measured in this way, the moon would be represented by the figure 8, the earth by 512, and tho sun by 1,303,000, 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, tho distance of the sun from the earth was 92.908,000 mbc--, and other methods of calculation had given approximately’ the same result, showing, in the words of Professor New combo, “ the striking correctness of the astronomical views of the earth.” Dealing with tho movements of tho 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. “If one could see the solar system from the outside, as it were, what a marvellous sight it would present,” continued Professor "White. “Here arc e'ghf planets, with attendant satellites, differing in size, at unequal distances, revolving in the some direction in orbits more or less eccentric and with varying velocity, all rotating with their axes at different angles to their planes, and in tho centre the gieat sun, vastly greater than all of them put together, holding them all in subjection to his power. And is i.t not really wonderful, too, that 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 stellar system is completely separated from tho rest of tho 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 the 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.) On the motion of the Rev. D. Dutton, seconded by Professor Jack, the lecturer was accorded a hearty vote of thanks. Mr R. Gilkison presided.