WORLD’S GREATEST

Taranaki Daily News, 7 October 1931, Page 2

WORLD’S GREATEST

CAMERA-TELESCOPE. TO FILM DARK STARS. ' A new telescope which is being built for the United. States Navy Department will have a range of 1,560,000,000 light years, and so far as photographic power is concerned, will be the greatest instrument of the kind in the world, although in size it is only about half as large as the telescope in the Mount Wilson Observatory, says the New York Times. The mirror is only 40 inches in diameter, as compared with'the 100 inches of the Mount Wilson telescope. “The new 40-inch telescope,” says the Bureau of Navigation in a new bulletin, “will photograph sky-sections in which the clear area, all of which will be accurate, is six times the diameter of the clear area in pictures that can be made with the largest telescope in existence tewday. Professor Ritehey says this means thirty-six times as much area of the sky can be studied on one plate. As a result he expects his instrument will make possible far more accurate charting of the skies than heretofore. “Improvements in the RitelieyG’hretien telescope will make it 90 per cent, efficient in photography, as compared with its theoretical optical power, whereas the largest and most powerful telescopes now in use are only 10 per cent, efficient in this respect. “This increased efficiency and power will be obtained by new types of mirrors, improved photographic plates, and super-refinements of operation. In the Ritchey-Chretien type telescope, the light from the stars first falls on a largo specially designed concave mirror, is reflected from that to a smaller specially designed convex mirror, and thence to the photographic plate. - “These mirrors will reflect clear images of stars over 1 the entire surface of the photographic plates instead of only near the centre as is the cose with, photographs taken with the present largest telescopes. “The emulsion for tho photographic plates to be used in the naval observatory telescope will be more sensitive than that now used. It will bo on glass plates ground with extreme accuracy to correspond to the curvature of the-ficld given by the new mirrors, instead of on onground glass plates as is now the practice, Ritchey explains. “Millions of individual stars in the enormous spiral nebulae as much as 6,0'00,009 light years distant from the earth will bo registered on these sensitive plates, it is expected. These spiral nebulae correspond to our own stellar system, the’Milky Way. _ Hundreds of thousands of these stars will be invisible to the naked eye on the plates, but when brought out by enlargement and magnification will be sharper and can be'more accurately measured than starimages in photographs made with methods now in use.” The new telescope is to be part ot the equipment of the naval observatory. It was designed.by Professor G. W. Ritchey, of California, and Professor Henri Chretien, of the University of Paris.