. The Adolfo Stahl lectures in astronomy, delivered in San Francisco, California, in 1916-17 and 1917-18, under the auspices of the Astronomical Society of the Pacific. ned to associate eclipses of the Sun and of theMoon with the motions of these bodies relatively to the Earth,and had indeed discovered an approximate method of fore-casting eclipses by means of an eclipse cycle, for which westill use the name they gave—the Saros. It is obvious that all the planets and satellites in our system,since they shine merely by reflected sunlight, must constantlybe attended by shadows sweeping through s
. The Adolfo Stahl lectures in astronomy, delivered in San Francisco, California, in 1916-17 and 1917-18, under the auspices of the Astronomical Society of the Pacific. ned to associate eclipses of the Sun and of theMoon with the motions of these bodies relatively to the Earth,and had indeed discovered an approximate method of fore-casting eclipses by means of an eclipse cycle, for which westill use the name they gave—the Saros. It is obvious that all the planets and satellites in our system,since they shine merely by reflected sunlight, must constantlybe attended by shadows sweeping through space on the sideturned away from the Sun, and that these shadows must beconical in shape (since the bodies casting them are approxi-mately spheres), with bases equal to the cross-sections of thebodies intercepting the Suns light, and lengths dependingupon the sizes and distances of these bodies from the night we walk in the Earths shadow, and, from amountain height, like that of Mount Hamilton, or from thedeck of a ship far out at sea, we can watch that shadow sweep-ing up the eastern sky as the Sun sinks farther and fartherbelow the western Fig. 5. Shadow and Penumbra of Earth and Moon. A marks the position of the Moon in a solar eclipse,B, in a lunar eclipse. An eclipse is total for points inthe shadow cones, partial for points within the penum-brae. A beautiful example of such a shadow is that afforded bythe passage of one of Jupiters larger satellites across theplanets disk. The shadow can be seen by our telescopes onlywhen it falls upon the planet, and then it appears as a nearlyround black dot which travels across the bright planet fromeast to west (Plate II). If we were on Jupiter within thatshadow-spot, the Sun would be eclipsed for us. Since the Moon revolves about the Earth from west toeast once every month, it must be in conjunction ( pass between A Total Eclipse of the Sun 55 the Earth and Sun) once each month—at new moon—andhalf a month la
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectastronomy, bookyear19
