Passing of the Shadow

On the morning of Jan. 24, in far northern Minnesota, the sun will not "rise." It will make its first appearance well above the horizon. For that is the day of the first eclipse of the sun in the northeastern part of the U. S. within memorable times. Already well-laid plans are under way for observing the eclipse. Scientists are broadcasting the event to the public in order to gather such data as lay observers can collect.

The Eclipse. All through the northeastern portion of the U. S. and Canada the sun will be partly eclipsed by the disk of the moon early on that morning. The area of complete eclipse--the area where the complete shadow of the moon will sweep over the East--brings in Minnesota at sunrise, thence moving southeastward in a gentle curve. It will cross northern Minnesota, nipping Duluth with its southern edge, cross the western tip of Lake Superior, include much of Wisconsin and Michigan on both sides of their joint border, skim over the northern third of Lake Michigan and the northern portion of Southern Michigan, glide over the lower half of Lake Huron, sweep across Ontario, picking up Toronto at its northern edge, span the approaching tips of Lakes Erie and Ontario, cross straight over Buffalo, darken northeastern Pennsylvania and southern New York, blanket nearly all of Connecticut and much of Rhode Island and go out to sea about 9:15 with Manhattan at its southern border. New Haven at its centre and New Bedford at its north flank; then out far across the Atlantic before taking a sweep north to end off at the Faroe Islands, north of Scotland.

The advantage of this itinerary is that it covers a populated area and a part of the world where there are already established observatories; too frequently eclipses take place in inaccessible places, where astronomical equipment has to be taken at great cost which may be entirely in vain if the day is cloudy. The next four total eclipses, for example, will take place in Sumatra, in Scandinavia, in Malacca, in Patagonia. But in this case, the observatories of Toronto, Cornell, Vassar, Yale and Wesleyan Universities will be in the path of the total eclipse while several others, such as the Yerkes and the Harvard observatories, will be in the region of partial but not of complete eclipse.

There are also disadvantages in the present eclipse. It will take place early in the morning, which is unfavorable, since the sun will be close to the horizon so that all light will come through the earth's atmosphere, at a great angle. Moreover, the region over which it passes is none too likely to have clear weather for observation purposes. At the hours of the eclipse and at the time of the year in which it takes place, the chance of clear weather at Buffalo is only 27%. The chance at Port Huron is 36%. The chance farther eastward in the belt of totality improves, with New Haven in about the most favorable position with 51% chance of clear weather. A third unfortunate factor is that the eclipse will be brief--less than two minutes.

The manner and the objects of observation of the layman are somewhat different from those of the scientist.

The Lay View. Armed only with a smoked glass, it is possible to see the disk of the sun gradually eclipsed by the moon. As more disappears, dusk comes on. Then it may be possible to see shadow bands playing across the land, a phenomenon the exact origin of which is not known. As the eclipse becomes almost complete, it may also be possible to see "Baily's beads." These are little spots of light coming through the valleys of the moon like strings of bright beads. This is as much as an observer in the region of partial eclipse can hope to see.

In the region of totality, the observer should turn his eyes westward along the earth. He must be careful not to have looked at the sun too much even through smoked glasses, or he will be unable to see the most important developments. Suddenly sweeping in from the West at great speed* will come the great shadow. Without waiting for it to arrive, he should turn to the sun. It will be totally eclipsed.

The period of totality will vary from only a few seconds to about two minutes in the favored points near the centre of the belt. During this brief period will be visible the rare sight of the sun's corona, ejections of gas driven out some millions of miles from the sun's seething fireball. This corona casts a ghostly light and exhibits itself around the dark rim of the moon, a glow from the sun at the inner ring, radiating outward in soft tints like a halo. Meanwhile, the sky is darkened and the stars are visible. Near the moon, and west of it, will appear a group of three planets, Venus nearest, then Mercury and farthest Jupiter. To be able to see Mercury with the naked eye is very rare, for its orbit is so near the sun that it is usually obscured by light when the latter is in the sky.

The main things that scientists hope to learn from lay observations are the exact borders of the totality belt and the times of the arriving of the total shadow and its departure, to the nearest second. These will help to improve knowledge as to the exact path of the moon.

The Scientific View. Meticulous obsenations will be made on many aspects of the phenomena accompanying the sun's eclipse. In many cases, the observations will cover a period extending a month before and a month after the event. One of the chief things to be studied is the sun's corona. Because it is visible only during the brief periods of total eclipses, there has probably been only about an hour made up of scattered minutes here and there, now and then, during which the corona has been under scientific examination. It is known to be connected with the phenomena of sunspots and electrical disturbances, but its exact nature is uncertain. The moon's course also will be closely examined to correct errors in present calculations; for, although the moon travels very regularly in a general way, it is slightly pulled aside this way and that by many diverse factors very hard to caculate. The effect of gravity on light rays, in accordance with the Einstein hypothesis, is one of a number of other phenomena to be observed.

Photographs were taken from airplanes in September, 1923, when a total eclipse took place in Southern California and Mexico. At that time, cloudiness spoiled every attempt at observation from the earth except for one expedition which had located itself in the interior of Mexico. So the aeronauts were practically the only ones who got any pictures. But their efforts were not highly successful. The results of using hand cameras in rapidly moving planes were not satisfactory. The apparatus has been improved, however, and better results are expected this time from airplanes, which will ascend at Dayton. Likewise the dirigibles Shenandoah and Los Angeles are expected to take the air this year and go out to sea, where the sun will be higher than on land at the time of the eclipse; in addition, they will have the advantage of slower movement than airplanes.

All good astronomers are burning candles to their Saints that the weather may be clear on the morning of Jan. 24.

*The shadow will travel at the rate of 60 miles an hour.