The Elements of Astronomy: A Textbook

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Сторінка 18 - ... is the great circle in which the plane of the earth's equator cuts the celestial sphere. It is often called the "Equinoctial.
Сторінка 219 - Venus a pea, on a circle 284 feet in diameter; the earth also a pea, on a circle of 430 feet; Mars a rather large pin's head, on a circle of...
Сторінка 178 - The radius vector of each planet describes equal areas in equal times. (3) The squares of the periods of the planets are proportional to the cubes of their mean distances from the su» ; ie, £12 : ia2 : : «!3 : a28. This is the so-called "Harmonic Law.
Сторінка 153 - From this, it is easily computed that the amount of heat received by the earth from the sun in a year is sufficient to melt a shell of ice 177.4 feet thick all over the earth's surface. 214. Solar Heat expressed as Energy. — Since according to the known value of the " mechanical equivalent of heat
Сторінка 401 - Power.—If we use the naked eye, we cannot see the image distinctly from a distance much less than a foot, but if we use a magnifying lens of, say, one inch focus, we can view it from a distance of only an inch, and it will look correspondingly larger. Without stopping to prove the principle, we may say that the magnifying power is simply equal to the quotient obtained by dividing the focal length of the object-glass by that of the eye-lens; or, as a formula M = — ; that is, — in the figure.
Сторінка 75 - Motion of the Pole of the Heavens around the Pole of the Ecliptic. — The obliquity of the ecliptic, which equals the angular distance of the pole of the heavens from the pole of the ecliptic, is not sensibly affected by precession.
Сторінка iv - The eminence of Professor Young as an original investigator in astronomy, a lecturer and writer on the subject, and an instructor in college classes, led the publishers to present the General Astronomy with the highest confidence; and this confidence has been fully justified by the event.
Сторінка 219 - Pallas, grains of sand, in orbits of from 1000 to 1200 feet; Jupiter a moderate-sized orange, in a circle nearly half a mile across; Saturn a small orange, on a circle of four-fifths of a mile...

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