The moon's shadow. while the eastern edge of the moon emerges into sunlight and the shadow is gradually left behind. Since the moon's diameter is a little more than one fourth that of the earth, and their distances from the sun are nearly equal, the moon's shadow is somewhat more than one fourth as long as the earth's. Its length varies because of changes in the moon's distance from the sun, caused chiefly by the varying distances of the earth, which carries the moon along with it. When the moon is between the other two bodies, its shadow is at times too short to reach the earth; at other times it is long enough and makes a small dark spot on the earth's surface. Since the moon is continually in motion, the shadow travels eastward over the earth; the earth is turning in the same direction. If the shadow is now falling on the city of New York, there is a race between the city and the shadow; but the latter is the swifter and passes out upon the Atlantic. A shot from a rifled gun would keep it company for a brief space of time. It is not often more than 150 miles in diameter, and cuts a pretty small swath on the earth's surface. Any one who establishes himself within the limits of A solar eclipse. the swath may see the sun totally eclipsed, if the sky be clear, during the time occupied by the shadow in passing over him. An observer near the path of the shadow may see the sun partially eclipsed. On rare occasions there is an interrupted view of the corona and prominences for six or eight minutes before the brilliant photosphere peeps out at one edge of the retreating. moon, and floods the landscape with light. Ordinarily the sun is entirely covered for only two or three minutes. A total solar eclipse is one of the most awe-inspiring phenomena of nature. The approach of the moon, which quietly eats its way into the solar disc, is not no For the sunlight is eclipse. ticed by those who are uninformed. so piercing that no special diminution of it is perceived A total solar until the eclipse is well advanced. At last the light begins to pale, as though a haze were forming over the sun. One who takes a quick upward glance, or employs a dark glass, sees that the sun is now a narrow crescent. The supreme moment is at hand; the landscape assumes an unearthly hue. The beholders are silent and stricken with awe. One stationed on a mountain may see the shadow advancing over the plain below with appalling speed. In but a moment it has come ; the moon hangs in mid-heaven, a ball of inky blackness, fringed with blazing prominences, and enveloped by the silvery corona. The moments are counted by heart-beats. The planets and brighter stars bedeck the sky; perchance a stray comet peers forth in the sun's vicinity. The upturned faces of the onlookers are ghastly. A piercing ray of light springs from the edge of the moon; the prominences are gone. The corona fades away; the stars return. The landscape glows with the returning light. The sublime spectacle is over. Effects on animals. It has not been without curious effects upon the lower orders of creation. The convolvulus closes its leaves, plants and birds cease flying, chickens go to roost, beasts leave their food, bees return to the hives, caged birds die of fright or thrust their heads under their wings, crickets sound their nocturnal notes, bats fly about; some horses seem to be overcome with fright and sink down in the street; others are blind to the changes about them, and go on without even pricking up their ears. Oxen have been known to arrange themselves in a circle, heads outward, as if fearing attack. Among semi-civilized or savage nations a solar eclipse Superstitious inspires great terror. Hindus believe that a great terror. Work during an eclipse. Small planets. dragon is striving to devour the sun. They fill the air with unearthly screams and shouts, and beat their gongs fiercely; the monster must be frightened away. Great is their joy when the voracious jaws eject the scorching morsel. We have gone far afield, and must return to summarize briefly some of the work which modern astronomers attempt during the fleeting moments of a total solar eclipse. I. The prominences and corona are observed telescopically. II. Spectroscopic observations are made of the corona, the protuberances, and the chromosphere. III. The light of the corona is studied with the polariscope; the purpose is to determine the relation between the light which the coronal particles reflect and that which they emit because of their incandescence. IV. A search for possible small planets revolving in the neighborhood of the sun, and usually hidden by its glare, is prosecuted. Reports of the discovery of such bodies have been the subject of rather acrimonious discussion. Professors Watson and Swift announced such discoveries during the eclipse of July 29, 1878, but no similar observations have been made at any succeeding eclipse. V. Photographs of the corona and of the prominences, being more trustworthy than hurried drawings, are much in vogue. CHAPTER XIII. MERCURY AND VENUS. 'Lo! in the painted oriel of the West, The evening star, the star of love and rest.” -Longfellow. MERCURY and Venus are denominated inferior plan- Inferior ets because their distances from the sun are less than planets. that of the earth. They are in conjunction when they appear to us to be nearly in line with the sun; the word conjunction suggests this. An inferior conjunction of Mercury or Venus occurs when the planet is between the sun and the earth; a superior conjunction takes place when the planet is beyond the sun. When at inferior conjunction a planet may come so near a line joining the centers of the earth and sun that it is seen against the background of the solar disc as a small black circle moving across its face. It is then in transit. After an inferior planet passes inferior conjunction it moves out toward the right as we stand facing the sun; it is then west of the sun, rising and setting before the sun does each day. In Fig. 107 S is the sun and E the earth, while the circle represents the orbit of Venus. When Venus is at Cit is in inferior conjunction. It then moves toward V, getting further and further to the right of the sun each week. When at V it has attained its greatest apparent distance west of the sun, and is at its greatest western Conjunction. |