Popular Lectures on Science and Art (Volume 1); Delivered in the Principal Cities and Towns of the United States

Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: ECLIPSES, Lunar and Solar Eclipses. Their Causes. Shadow of the Earth. And Moon. Magnitude of Eclipses. When they can happen. Central Solar Eclipie. Great Bolar Eclipse described by llalu-y Ecliptic Limits. ECLIPSES, Op all the occasional astrononomical phenomena, those which have attracted roost popular attention are Lunar and Solar Eclipses. We shall on the present occasion explain the principal circumstances attending them. When a luminous body, radiating light in all directions around it, throws these rays upon an opaque body, that body prevents a portion of the rays from penetrating into the space behind it. That portion of the space from which the light is thus excluded by the interposition of the opaque body, is called in astronomy the Shadow of that body. The shape, magnitude, and extent, of the shadow of an opaque body, will depend partly on the shape and magnitude of the opaque body itself, and partly on that of the body from which the light proceeds. In the cases before us, the form of the bodies are globes. If the globe of the Sun were equal in magnitude to the globe of the earth, the shadow of the latter would be a cylinder, the base of which would be equal to a great circle of the earth, and such shadow would be interminable, since its sides would be parallel. This will be evident by an inspection of the annexed figure, 1, in which S. represents the sun, and E. the earth; the rays S. E. forming the sides of the shadow, being parallel, could never meet, and consequently the shadow would be infinite, since light can never penetrate into the space between them. If, on the other hand, the sun were a globe less in magnitude than the earth, then the shadow of the latter would hare diverging sides as represented in the annexed figure, 2, which would wide...