ASTRONOMICAL STUDY

Evening Star, Issue 25618, 19 October 1945, Page 7

ASTRONOMICAL STUDY

OTAGO SOCIETY’S MEETING TWO INTERESTING ADDRESSES Activities of the astronomical branch of the Royal Society of New Zealand (Otago branch)' were reviewed by the chairman, Mr W. D. Anderson, at the annual meeting held last night at the Museum. He mentioned the recent formation in Dunedin of a Telescope Makers’ Olub, which \ he ventured to say, was the only amateur body of its kind in the southern hemisphere. There was an enthusiastic membership, lie said ; and good work was being accomplished for the advancement of astronomy in Dunedin. The following office-bearers were elected for the ensuing year:—Chairman, Mr W. D. Anderson, F.R.A.S.; vice-chairman, Mr J. C. Begg, F.R.A.S.; hon. secretary and director of the observatory, Mr G. G. Couling; hon. treasurer, Mr W. D. Anderson; committee—Drs C. M. Focken and S. B; Strain, Messrs D. C. Berry, F. E. W. Chrisp, W. H. Drew, G. S. Smith, W. Gardner, E. G. McGeorge, and J. Riach; representative on the Council of the Royal Society, Mr D. C. Berry. NAVIGATION BY AIR. An address on the methods of navigation used in the air, with special emphasis on astral navigation, was given by Mr A. J. Maclvor, who during the war had served with the R.N.Z.A.F. in the Pacific. The speaker traced the growth of navigation in relation to the evolution of aircraft, describing the method of map-reading used when the plane had only to cover an area of land. When flights were attempted further afield, however, over desert or sea, the normal map-reading system was not sufficient, and some other method had to be employed. Some aspects of marine navigation were borrowed, therefore, and these remained the basis of air navigation today. The speaker dealt witli the method of dead reckoning. used in the air, explaining the various difficulties, such as wind drift, magnetic variation, and deviation, encountered in a moving aircraft, after which he. outlined the method by which a position was obtained at any time. Astronomical reckoning had been mostly used in the Pacific, as the other alternatives—radio and radar—had not been fully available in his area. Mr Maclvor pro-

i duced a bubble sextant of a type used t>v the Royal New Zealand Air Force, and illustrated the .method of sighting the desired heavenly body. As a further illustration of the work entailed in navigating a plane he showed his audience an astral compass, used to check the reading of the magnetic compass, which lost its accuracy by the magnetic field set up in the aircraft. Tile methods used in the Air Force for astronomical reckoning were tpe simplest possible, the speaker added, because of the conditions under which the navigator was operating in the combat areas. METEORITES. The average meteors which tin eartn's atmospnere collected in tin •lourse of a clay were tiny missi.es vital Mr G. U. Couiing, but sometnine; i rorn out of the deptns of space tin speeding earth encountered large: meteors, whose weight was measured in pounds, or even tons, instead .oi grains or ounces. These bodies, which were not completely dissipated before reaching the ground, were known as meteorites. . * Falls of meteorites in populated areas were rare, and the first known to strike an automobile or terrestrial vehicle of any kind did so an Illinois in 1938, when a four-tpound celestial stone crashed through a garage roof and into a car. The largest known meteorite crater on the earth, Mr Couling said, was located in North-central Arizona, being "nearly three miles in circumference, about four-fifths of a mile in diameter, and almost 600 feet deep. Conclusions drawn from all the principal theories advanced were that the crater was made by a great cluster of meteorites, comprising . thousands of iron shale balls, weighing in all not less than 1,000,000 tons, and moving with a velocity of from 15 to 30 miles per second. The amount of rock displaced and partly thrown out of the crater had been estimated at more than 300.000,000 tons. In conclusion, the speaker touched oil other famous craters on the surface of the earth, also describing a few of the largest meteorites known to the scientific world. He displayed to his audience the meteorite, weighing 131b' 7oz. which was discoyered near Morven. in Canterbury.