Eclipse, e-klips', a term applied to the cutting off of the light of the sun from a heavenly body. An eclipse of the moon is caused by the passing of the earth between the sun and the moon. The moon is in the earth's shadow. An eclipse of the sun is caused by the passing of the moon between the sun and the earth. The earth is in the moon's shadow. The observer cannot see the sun for the moon. Since the earth is smaller than the sun its shadow comes to a point 857,000 miles away. At the point where the moon passes through the shadow its width is about two and two-thirds times the diameter of the moon. It is possible for a total eclipse of the moon to last about two hours. Even during a total eclipse the moon is not entirely obscured, but shines with a dull, copper-colored light. For a similar reason the shadow of the moon is also a cone, averaging 232,000 miles in length. At times the moon is farther than this from the earth, and it is not possible for an eclipse of the sun to take place. When conditions are most favorable, the earth enters the moon's shadow at a point where the cone is 168 miles in diameter. A total eclipse of the sun is possible, therefore, only along a belt of this width. As a matter of fact, the region within the moon's shadow is usually an oval figure having this length, but having a width not to exceed sixty or seventy miles. During a total eclipse the disc of the sun is entirely concealed within the limited region mentioned. The track of this oval shadow across the continent is called the belt or path of the eclipse. The greatest number of eclipses possible in any one year is seven. The lowest number possible is two. The usual number is four. In 1917 there will be four eclipses of the sun and three of the moon. In 1935 there will be two of the moon and five of the sun. As a total eclipse of the sun affects but a small area, any particular portion of the earth's surface is likely to be within its path only once in about 360 years. The next total solar eclipse visible in the United States will occur in 1918. Subsequent dates are 1923, 1925, 1930, 1945, 1954, 1979, and 1984. Whether partial or total, an eclipse is an interesting phenomenon. During a lunar eclipse the moon assumes a weird, spectral appearance. During a solar eclipse the blackness which comes over both the sun and the earth is truly appalling. According to a statement of a writer who was an eye witness of a solar eclipse visible in the Southern States during the early half of the nineteenth century, the blackness of the landscape was simply beyond description. Cattle roamed the pastures or stood in astonishment; chickens went to roost. Negroes prostrated themselves in terror and cried for mercy, thinking the end of the world was at hand. Astronomers seize upon a solar eclipse as a favorable opportunity to study the sun. Scientific expeditions are sent out from learned institutions to the favored region, even to remote parts of the world, when a total eclipse is due. The work of observing an eclipse is now systematized thoroughly. The most important duty during the hour is that of taking photographs for future study. See SUN; MOON.