The Great Shadow

Total Eclipse. The approaching total eclipse of the sun (TIME, June 11) on Monday, Sept. 10--easily the most important astronomical event of the year--continues to arouse the most intense interest in scientific circles and unprecedented preparations are under way for its reception and entertainment during the 3 minutes, 36 seconds it will be the guest of the Western Hemisphere. This period of totality is about the average for all total eclipses. The greatest possible duration of a total eclipse is 7 minutes, 58 seconds, and this occurs only under very exceptional circumstances. The solar eclipse of September, 1922, observed in Australia, lasted about five minutes, while that of 1918 was only two minutes long. The " belt of totality " of the coming eclipse will be about 100 miles wide. It will pass in a wide curve across the Pacific southeasterly from Kamchatka, touching the mainland of the U. S. at only two points--Point Concepcion (on the California coast just above Santa Barbara) and the vicinity of San Diego at the extreme Southwest corner of the state. Thence it sweeps diagonally across Mexico and Yucatan and on out into the Caribbean and Atlantic, crossing some of the West Indies. The Santa Catalina Islands, off the Southern California coast, are directly in the path of totality, and one of them, San Clemente, is exactly on the center line, with practically the total possible duration. In Mexico other advantageous points for viewing the eclipse are at Ensenada (in Lower California), Hermosillo (in Sonora), Cuencame (in Durango), Berrendo (in San Luis Potosi). In other parts of the U. S. the eclipse will have varying degrees of totality--99% at Los Angeles, 71% at Denver, 60% at St. Louis, 52% at Chicago, 64% at Atlanta, 46% at New York, 42% at Boston. No part of the eclipse will be visible in Europe. The passage of the moon's shadow from one edge of the sun's disk to the other will take about 2 hours and 55 minutes in the path of totality, but less than 2 hours in the Eastern states. As this will occur in California and Mexico shortly after noon--the best part of the day for observation--exceptional opportunities will be offered.

Expeditions. The scientific expeditions which will observe the eclipse in California and Mexico are multiplying rapidly. They include:

1) The leading American expedition will be headed by Dr. John A. Miller, Vice President of Swathmore College and Director of its Sproul Observatory. It will be stationed at Yerbaniz, Mexico. Other members: Profs. E. W. Merriott and W. E. Wright, of Swathmore; Prof. Heber D. Curtis, Director of the Allegheny Observatory, University of Pittsburgh; Prof. Dinsmore Alter, University of Kansas. They will take a 65-foot focal length telescope camera, the largest ever used for this work.

2) The Yerkes Observatory expedition headed by Director Edwin B. Frost and Captain Barnett Harris, of the War Department, will take motion pictures of the eclipse with four cameras placed 15 miles apart. They will be stationed on Santa Catalina Island.

3) The Mt. Wilson Observatory expedition, of the Carnegie Institute, of Pasadena, Cal., headed by Dr. Walter S. Adams, will observe the eclipse from two stations besides the main observatory, including one at Point Lonia, near San Diego. About 98.5% of the sun's disk will be covered at Mt. Wilson, and observations will be made there with the great Snow telescope and a 50-foot interferometer now under construction for the measurement of star diameters.

4) The Lick Observatory, under its Director, Dr. W. W. Campbell, will observe the eclipse from the main observatory and from a station at Ensenada, Lower California.

5) The Steward Observatory expedition, of the University of Arizona, under Director A. E. Douglass, will be located south of Hermosillo, Mexico.

6) The Washburn Observatory expedition, University of Wisconsin, will be on Santa Catalina Island.

7) The Goodsell Observatory expedition, Carleton College, Northfield, Minn., will observe from Santa Catalina Island.

8) The Mexican Government expeditions, under Professor Gallo, Director of the National Observatory at Tacubaya, will occupy stations at Cuencame and Berrendo.

9) The German expedition, under Dr. Hans Ludendorff, brother of the general, will be stationed in Durango as guests of the Mexican Government.

10) The Paris Observatory expedition, under Camille Flammarion, will also be in Mexico. M. Flammarion thus adds another chapter to his eventful history that began in 1842 in the reign of Louis Philippe. At four he could read. At six he had completed what is equivalent to a grammar school education. His astronomical career was determined by the occurrence of two eclipses of the sun--one when he was five, the other when he was nine. He went to Paris and studied, "on nothing a year." He passed the examinations for the Observatory and at 16 was the author of the first of his numerous works, a treatise on the Cosmos. His remarkable career is best explained by a sentence from his own memoirs: "To learn, to learn without end, for the sole pleasure of knowing, has always been the dominant passion of my spirit."

11) Many amateur and unofficial groups will observe the eclipse from various points in its path. The federal and state officials of Mexico, the National Railways, local astromomers are offering every possible courtesy to the visiting scientific men. The wireless station at Chapultepee Castle, Mexico City, will be opened for the benefit of the astronomers.

Objectives. Three principal objectives will be in the minds of the observers during the passage of the eclipse:

1) Further direct proof of the Einstein predictions regarding the deflection of light rays from stars close to the edge of the sun's disk. (TIME, April 21.) The Lick Observatory expedition at Wallal, Australia, during the solar eclipse of last September, obtained what Dr. Campbell considered thoroughly satisfactory verification of the Einstein effect, and will make no special attempt to photograph it. Most of the other expeditions, however, will devote special attention to this phenomenon.

2) Study of the sun's corona, the fiery streamers which shoot out from the sun's surface, sometimes to a distance of 80,000 miles, but can best be observed only during a total eclipse, when the sun's disk itself is obscured but the corona forms an outer ring of light around it. Some astronomers believe the corona is a mass of matter held in space by some electromagnetic force. Others think it is composed largely of gaseous matter shot out by explosions from the sun. There will be an excellent chance to determine the chemical composition of the corona accurately by means of the spectroscope on Sept. 10. It is fairly certain that it contains both gas and a metal, called coronium, which is unknown on the earth, but somewhat resembles iron. By these studies it is hoped to learn something of the nature of atomic energy both in the sun and on the earth.

3) Determination of the cause of the moon's aberration in its orbit at certain times. Eclipses can occur only when the moon is at the nodes of its orbit, the points 180DEG apart where it crosses the plane of the earth's orbit. This occurs every month, but only if the earth, moon and sun are in line will there be an eclipse. There are always two solar eclipses each year, and sometimes as many as five, but eclipses visible as total on the earth are comparatively rare, and the present event is the best opportunity for observation that has been offered for several years.

Many new methods will be utilized for the first time in the observation of this eclipse. Col. John Millis of Cleveland, has suggested to the superintendent of the U. S. Naval Observatory the use of airplane photographs of the earth's surface under the shadow bands of the eclipse.