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altitude angle angular distance apparent position appear astronomical atmosphere attraction axis brighter called celestial equator celestial meridian celestial pole celestial sphere centre circle comet constellation determine diameter direction disk diurnal motion diurnal orbit earth earth's surface east equator figure fixed stars force gravitation Greenwich heat heavens Hence horizon hour-angle inferior conjunction interval Jupiter Kepler kilometres known latitude length light longitude lunar magnitude Mars mass mean distance mean solar measured Mercury meteoroids meteors miles months moon moon's move naked eye nearly nebulae Neptune node noon north pole north-polar distance object observer orbit parallax particle pass period phenomena photosphere planet radiation radius rays refraction revolution revolves right ascension ring rotation satellites Saturn seen shadow sidereal solar system spectroscope spectrum sun's supposed telescope terrestrial theory tion transit Uranus vapor variable stars velocity Venus vernal equinox visible zenith
Page 119 - 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 115 - The change of motion is proportional to the motive force impressed; and is made in the direction of the right line in which that force is impressed.
Page iii - Aims to furnish a tolerably complete outline of the astronomy of to-day, in as elementary a shape as will yield satisfactory returns for the learner's time and labor. It has been abridged from the larger work, not by compressing the same matter into less space, but by omitting the details of practical astronomy, thus giving to the descriptive portions a greater relative prominence. From THE CRITIC: " The book is in refreshing contrast to...
Page 109 - law of equal areas." (3) The squares of the periods of revolution of any two planets are proportional to the cubes of their mean distances from the sun.
Page 320 - ... and, calling this a sidereal stratum, an eye placed somewhere within it will see all the stars in the direction of the planes of the stratum projected into a great circle, which will appear lucid on account of the accumulation of the stars; while the rest of the heavens, at the sides, will only seem to be scattered over with constellations, more or less crowded, according to the distance of the planes or number of stars contained in the thickness or sides of the stratum.
Page 176 - Its satellite system also deserves careful observation, especially in respect to the eclipses which occur; since we find in them a measure of the time required for light to cross the orbit of the earth, and so of the solar parallax, and also because, as has been already mentioned, they furnish a test of the constancy of the earth's rotation. The photometric method of observing these eclipses, first instituted by Professor Pickering at Cambridge in 1878, and since re-invented by Cornu in Paris, has...
Page 115 - Every body continues in its state of rest, or of uniform motion in a right line, unless it is compelled to change that state by forces impressed upon it.
Page 104 - KEPLER (born 1571, d. 1630) was a genius of the first order. He had a thorough acquaintance with the old systems of astronomy and a thorough belief in the essential accuracy of the Copernican system, whose fundamental theorem was that the sun and not the earth was the centre of our system.