Maps & Moon Shadow

Along a great arc sweeping from the equator in mid-Atlantic to Irkutsk in central Siberia, the sun will be in total eclipse on Feb. 25. Last week an expedition of scientists from the U.S. Air Force, the Naval Research Laboratories, the National Geographic Society and the Universities of Denver and Colorado set out for way stations on the eclipse's 70-mile-wide path. When the moon's shadow climbs northeastward over half the world, the experts will be waiting with telescope, camera and electronic recording equipment. By their observations they hope: 1) to correct their maps and charts, 2) learn something about weather prediction and radio communication, 3) check on a prediction made by Albert Einstein some 37 years ago.*

At stations, spotted from Libreville in French Equatorial Africa to the Persian Gulf, Air Force observers will measure the fading sunlight. Even in bad weather their photoelectric cells and elaborate timing devices will be able to record the instant of total eclipse. Knowing the speed with which sun and moon move in relation to the earth, they hope to calculate the distance between stations with new accuracy.

New Job. Observations will also be made at Dhahran, Saudi Arabia, outside "the path of totality." If the instruments prove sensitive enough even in a partial eclipse, the Air Force may face a vast new job of map making. And since guidance systems for intercontinental rockets already threaten to become more accurate than present charts of large sections of the world, new maps are fast becoming a necessity.

Within the next 15 years there will be a score or more solar eclipses, their paths interlacing over the surface of the globe. If the areas of partial eclipse turn out to be useful for measurement, it should be possible to man a network of observation posts during each one. Enough observations, says the Air Force, may eventually produce enough information to change most of the world's atlases.

Old Theory. While the Air Force goes about its map making, Astronomer George Van Biesbroeck will be busy at Khartoum in the Anglo-Egyptian Sudan, checking up on Einstein's theory. During the three minutes of total eclipse, he will aim his telescope at the faint star field ordinarily blotted out by the sun's brilliance.

A few months later, his telescope locked in the same position, the astronomer will return to Khartoum and photograph the same star field in the night sky. Comparison of the stars' positions in the two pictures should illustrate the "Einstein Shift," give man one more glimpse into the mechanics of the universe.

* One proof of his theory of relativity, Einstein said, would be the observation of a slight bending of light rays from distant stars as they pass through the gravitational field of the sun.

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