Astronomy for Everybody

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Page 259 - that every particle of matter in the universe attracts every other particle, with a force whose direction is that of the line joining the two, and whose magnitude is directly as the product of their masses, and inversely as the square of their distances from each other.
Page 167 - AND ASPECTS OF THE PLANETS THE orbits in which the planets revolve around their central luminary are in strictness ellipses, or slightly flattened circles. But the flattening is so slight that the eye would not notice it without measurement. The sun is not in the centre of the ellipse but in a focus, which in some cases is displaced from the centre by an amount that the eye can readily perceive. This displacement measures the eccentricity of the ellipse, which is much greater than the flattening....
Page 266 - ... it, astronomers on the earth can observe the attraction of the planet on its satellites and thus determine its mass. The rule for doing this is very simple. The cube of the distance between the planet and satellite is divided by the square of the time of revolution of the satellite. The quotient is a number which is proportional to the mass of the planet. The rule applies to the motion of the moon round the earth and of the planets round the sun. If we divide the cube of the earth's distance...
Page 173 - ... it is exceeded by some of the minor planets to be hereafter described. In consequence, its distance from the sun varies between wide limits. At perihelion it is less than twenty-nine millions of miles from the sun; at aphelion it goes out to a distance of more than forty-three millions of miles. It performs its revolution around the sun in a little less than three months; to speak more exactly, in eighty-eight days. It therefore makes more than four revolutions in a year. Performing more than...
Page 319 - ... having for its centre the point in which the star would be seen if the earth were at rest. Hence, in all very nice calculations and determinations of the positions of the stars, allowance must be made for the effects produced by aberration.
Page 125 - Every square foot in the earth's interior sustains a pressure equal to the weight of a column of the earth a foot square extending to the surface.
Page 121 - ... and larger every year that we go back into its history. There was a time when it must have been as large as the whole solar system. In this case it could have been nothing but a nebula. We thus have the theory that the sun and solar system have resulted from the contraction of a nebula — through millions of years. This view is familiarly known as the nebular hypothesis. The question whether the nebular hypothesis is to be accepted as a proved result of science is one on which opinions differ....
Page 18 - ... sweeps over the whole celestial sphere. The appearance to us is that every point of the celestial sphere crosses the meridian in the course of a day. Noon is the moment at which the sun passes the meridian. Before the introduction of railways, people used to set their clocks by the sun. But owing to the obliquity of the ecliptic and the eccentricity of the earth's orbit around the sun, the intervals between successive passages of the sun arc not exactly equal.
Page iii - Magazinr [nos. 241, 245, 253] a few years since on the unsolved problems of astronomy, total eclipses of the sun and other subjects.

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