National Geographic : 1955 Sep
New Light on the Changing Face of Mars A Huge Green Area Almost the Size of Texas Appears in Photographs Made by the National Geographic Society-Lowell Observatory Mars Expedition to South Africa BY E. C. SLIPHER Astronomer, Lowell Observatory, Flagstaff, Arizona, and Leader of the 1954 National Geographic Society-Lowell Expedition 427 USUALLY an expedition to Africa aims at big-game hunting, missionary work, or exploration. In the spring of last year, however, one set out for Bloemfontein, South Africa, on the strange mission of ex ploring another world. This other world was the planet Mars, which would spin closer to the earth that summer than it had done for 13 years-a mere 39,800,000 miles away on July 2, 1954 (see diagrams, page 430).* To Africa for a Grandstand Seat With the coordinating aid of the new Inter national Mars Committee, scientists in many countries seized the chance to renew their attack on stubborn secrets of our red-and green-faced neighbor. For example, they were eager to learn more about the amazing changes which sweep across its face con tinually, and particularly what causes vast areas to turn blue-green in Martian summer. To us of Lowell Observatory, this chance was particularly appealing, for Mars has been a favorite target of our telescopes since the days of our founder, Percival Lowell. He advanced the theory that the faint lines called canali by their Italian discoverer are strips of vegetation along watercourses, and that the planet is being irrigated from the melting ice caps by intelligent beings struggling to keep alive on a dying planet. But to make full use of this golden chance to gain more information, we needed a grand stand seat in the Southern Hemisphere. Mars would lie so far south during the crucial months that the great telescopes of the North ern Hemisphere would be able to observe it for only a short period each night and at a low elevation above the horizon, where turbulence of the earth's air interferes with what astronomers call "seeing." Fortunately, the University of Michigan made available to us its excellent 27-inch refracting telescope, the largest in the South ern Hemisphere, at its observatory's southern branch, Lamont-Hussey Observatory in Bloemfontein, South Africa. Here Mars would appear almost overhead each night, and we would have the longest and best possible type of seeing, through the shortest path of clear, dry South African air. Greatly impressed by these prospects, the Lowell Observatory brought the matter to the attention of the National Geographic Society, whose generous assistance to worth while projects is widely known. The officials of The Society quickly recognized the need and the scientific importance of such an undertaking and agreed to sponsor, jointly with us, a six-month expedition to Bloem fontein for intensive study of the planet. In our conferences with The Society's offi cers and Research Committee, it was agreed that the most valuable contribution to knowl edge of Mars would be a complete and con tinuous set of photographs taken during the five best months of the opposition in at least three colors-blue, yellow-green, and red. Blue Filter Reveals Martian Clouds Photographers well know that by the use of various colored filters they can reveal dif ferent aspects of a landscape or sky and penetrate haze. We applied the same tech niques in probing the nature of Mars. Blue filter photographs best reveal the planet's clouds, for instance, while a red filter helps us detect changes in the blue-green regions. Carefully calibrated photographs, we hoped, would give us more accurate knowledge of the size and shape of Mars, known to be about 4,220 miles in diameter, or roughly half that of the earth. The program called for special types of plates, filters, cameras, and lenses-all of which were either built or adapted at the Lowell Observatory in Flagstaff to fit the Lamont-Hussey telescope. We shipped our heavy supplies from Flag *See "News of the Universe," by F. Barrows Colton, NATIONAL GEOGRAPHIC MAGAZINE, July, 1939.