Science: Tragic Eclipse

To many astronomers, the most precious moments in the stream of time are the fleeting minutes and seconds of a total solar eclipse, during which they must make their photographs and observations. It is theoretically possible for an occultation of the sun by the moon to last as long as 7 min. 30 sec., but most are several minutes shorter than that. Last year’s June eclipse, for example, whose shadow path across Asia was studded with astronomers’ observation camps (TIME, June 22), lasted only 2 min. 31½ sec. at maximum. There was a tragic irony about the eclipse which on Tuesday of this week passed for thousands of miles across the tropical wastes of the Pacific Ocean. At its noon point, totality lasted 7 min. 4 sec., longer than any eclipse since the rise of modem astronomy, longer in fact than any since the year 699 A. D. But the noon point was 1,800 miles from any land. Precision measurements from the swaying deck of a ship are out of the question.

This week’s eclipse touched almost no land at all. Starting in the open sea at sunrise, it darkened the tiny specks of the Phoenix Islands shortly after 8 a. m., then the shadow rolled on across the sea, stabbing into Peru just before it ended at sundown. In the Phoenix Islands totality lasted 3 min. 35 sec. In Peru, where it lasted 3 min. 24 sec., the sun was only 8° above the horizon during totality and its darkened image was distorted by late afternoon haze. Nevertheless eclipses offer such fine opportunities to scientists to study the composition and behavior of the sun’s outer envelope and to photograph the magnificent flare of the corona, that expeditions were waiting for the shadow at both these meagre vantage points. Two astronomers—James Stokley of Philadelphia’s Franklin Institute and John Quincy Stewart of Princeton—decided to go to the point of maximum duration in a 6,000-ton freighter. They planned to take snapshots with hand cameras, note the direction and length of the corona’s streamers and take brightness measurements with photoelectric cells. Whatever the value of these observations, they could at least say they had seen a longer eclipse of the sun than any other astronomers of modern times. The better to see in the eclipse darkness, they said they would blindfold themselves for half an hour before totality started. For Dr. Stewart the ship’s carpenter built a special chair, inclined far back so that he could look nearly vertically overhead in comfort.

Total solar eclipses occur on the average about once every 18 months somewhere on earth. Any given spot should have one once every 360 years. The size of the shadow and hence the rapidity with which it passes a given point vary because, the earth’s orbit around the sun and the moon’s orbit around the earth being elliptical, the earth-sun and earth-moon distances vary. For a long eclipse, the sun must be near its maximum swing of over 94,000,000 miles (mean distance: 92,900,000 mi.) and the moon near its minimum distance of 218,000 miles (mean: 235,000 mi.). This condition occurred this week. When the sun is farther away than usual, the shadow cone beyond the moon is longer; and when the moon is closer to earth than usual, the earth intercepts a thicker section of the cone. The maximum possible width of an eclipse path is 167 miles. At its noon point the shadow path of this week’s eclipse was 153 miles wide.

Another factor affecting totality duration is that the shadow travels slowest at noon, fastest near the beginning and end of the eclipse day. Earth rotates eastward at about 1,040 m.p.h. at the Equator. The moon’s eastward orbit carries the lunar shadow in the same direction at just about twice that speed, so that it rapidly overtakes the terrestrial rotation. At noon, when the shadow is perpendicular, the speed is 1,060 m.p.h.; earlier and later, when the cone of darkness impinges at an angle, it goes faster—depending on the acuteness of the angle.

Five expeditions were on hand in Peru this week to make the best of the late afternoon performance—one Peruvian, one Japanese, three U. S. Pan American-Grace Airways, Inc. lent an airliner to take a group of observers up 30,000 ft. into the crystal clarity of the substratosphere. At the other end of the eclipse path, the National Geographic Society-U. S. Navy Expedition set up camp on Canton Island in the Phoenix group, inhabited mainly by millions of rats (descended from shipwrecked ancestors). This party was equipped with a new material for measuring the polarization of the coronal light, a newly invented spinning filter for taking improved pictures of the corona, air conditioning equipment to keep the film cool and dehumidify the developing room, three NBC men to broadcast the performance to the world.

By crossing the International Date Line, the eclipse accomplished the feat—not rare for eclipses—of ending the day before it started. It began on Wednesday, finished on Tuesday. Since it crossed the Equator twice and also the 180th meridian, it entered four hemispheres. Most curious of all, although until this week there had been no seven-minute-plus eclipse in 1,200 years, there will be two more of them in the 20th Century—one in Ceylon, Siam and the Philippines in 1955, the other in South America and Africa in 1973. The U. S., however, will get only one piddling 65-sec. affair for the rest of the century. Year: 1963. Witness: New England.