An Elementary Treatise on Astronomy: Adapted to the Present Improved State of the Science, Being the Fourth Part of a Course of Natural Philosophy, Compiled for the Use of the Students of the University at Cambridge, New England |
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Common terms and phrases
altitude angle apogee apparent diameter Astron astronomers calculate called celestial sphere centre circle circle of latitude comets consequently consider declination deduced described determine direction disc diurnal motion earth eccentricity ecliptic effect epoch equal equator equinoctial point exactly formulas greatest heavenly bodies heavens horary horizon horizontal parallax inclination instant interval Jupiter latitude laws light luminous lunar manner mean distance mean longitude mean motion Mercury meridian moon moon's nearly node nutation obliquity observations obtain opposite orbit parallax parallel passes perceive perigee periodical inequalities perpendicular phenomena plane pole position preceding precession proper motion quantity ratio reckoned refraction respect retrograde right ascension satellites Saturn secular seen semidiameter shadow sidereal day sidereal revolution situated solar solstice spherical spots stars straight line sun's suppose surface tables take place tang telescope terrestrial tion triangle tropical true variations velocity Venus vernal equinox vertical visual ray zenith distance
Popular passages
Page 291 - ... that the mean longitude of the first satellite, minus three times that of the second, plus twice that of the third, is always equal to two right angles.
Page 314 - That every planet moves so that the line drawn from it to the sun describes about the sun areas proportional to the times, 2.
Page 346 - Each planet moves in an ellipse in one focus of which the sun is situated. 3. The squares of the periods of revolution of the planets are proportional to the cubes of the major axes of the ellipses.
Page 128 - That node where the planet passes from the south to the north side of the ecliptic, is called the ascending node ; and the other is the descending node.
Page 362 - Mayer, who compared the places of eighty stars as determined by Roemer with his own observations, and found that the greater part of them had a proper motion. He likewise suggested that the change of place he had observed among these stars might arise from a progressive motion of the sun towards one quarter of the heavens. La...
Page 259 - Jth of the celestial hemisphere, after which it begins to return ; and as we can ordinarily discern it with the naked eye only when the sun is below the horizon, it is visible only for a certain time immediately after sunset. By and by it sets with the sun, and then we are entirely prevented from seeing it by the sun's light. But after a few days, we perceive, in the morning, near the eastern horizon, a bright star which was not visible before. It is seen at first only a few minutes before sunrise,...
Page 306 - There are some whose plane is nearly coincident with that of the ecliptic, and others have theft planes perpendicular to it. " It is farther to be observed that the tails of comets begin to appear, as the bodies approach near the sun ; their length Increases with this proximity, and they do not acquire their greatest extent, until after passing the perihelion* The direction is generally opposite to the sun* forming a curve slightly concave, the sun on the concave side.