The Elements of Astronomy: Or, The World as it Is, and as it AppearsCrocker and Brewster, 1850 - 376 pages |
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Page 17
... give the arc , the arc will always have the same proportion to its circle , and this proportion gives the same number of degrees for the measure of the angle . If we make in the edge of a ruler five notches , and turn the ruler round ...
... give the arc , the arc will always have the same proportion to its circle , and this proportion gives the same number of degrees for the measure of the angle . If we make in the edge of a ruler five notches , and turn the ruler round ...
Page 19
... gives to plumb lines a convergence of about a minute . § 17. The zenith and nadir are the poles of the celes- tial horizon ; that is , they are points 90 ° distant from every point in it . The celestial horizon is the vanishing line of ...
... gives to plumb lines a convergence of about a minute . § 17. The zenith and nadir are the poles of the celes- tial horizon ; that is , they are points 90 ° distant from every point in it . The celestial horizon is the vanishing line of ...
Page 29
... give it great apparent magnitude , it becomes indistinct ; because the rays diverge from each point so much that the eye cannot bring them to a focus . But if we can make the rays from it enter the eye nearly parallel , it will be ...
... give it great apparent magnitude , it becomes indistinct ; because the rays diverge from each point so much that the eye cannot bring them to a focus . But if we can make the rays from it enter the eye nearly parallel , it will be ...
Page 31
... gives us four minutes as the time an object in the celestial equator would take to pass the mouth of the tube if it only takes in one degree of the heavens . In ordinary telescopes the field of view is about half a degree , and an ...
... gives us four minutes as the time an object in the celestial equator would take to pass the mouth of the tube if it only takes in one degree of the heavens . In ordinary telescopes the field of view is about half a degree , and an ...
Page 35
... give steadiness , and to prevent its being affected by the wind ; for every vibration will be increased in the same ratio as the amplification of the instrument , and produce a tremulous or dancing motion in the objects . Thus a supe ...
... give steadiness , and to prevent its being affected by the wind ; for every vibration will be increased in the same ratio as the amplification of the instrument , and produce a tremulous or dancing motion in the objects . Thus a supe ...
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The Elements of Astronomy, Or the World as It Is, and as It Appears (Classic ... Anna Cabot Lowell No preview available - 2016 |
Common terms and phrases
aberration altitude angular aphelion appear ascertained astronomical atmosphere attraction axis body called cause celestial centre of gravity centrifugal force circle cluster comet constellations curve degree density described diameter direction disc distance disturbing double star earth earth's surface eccentricity ecliptic equal equator equatorial equinoctial feet fixed stars globe greater heat heavens hemisphere horizon illuminated inclined increase inequalities Jupiter Jupiter's latitude length less light longitude lunar mass mean measure meridian miles minutes moon moon's move nearer nearly nebulous nodes nutation object obliquely observed parallax parallel passes perigee perihelion period perpendicular planets polar pole portion position proper motion proportion radius rays refraction revolution revolve right angles right ascension rise rotation satellites Saturn seen shadow side sidereal sidereal day solar eclipse solar system space sphere spherical sun's suppose telescope tion Uranus vapor variations velocity Venus vernal equinox vertical visible whole zenith
Popular passages
Page 344 - ... 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 37 - Now, suppose the head of the screw to be a circle, whose diameter is an inch, the circumference of the head will be something more than three inches : this may be easily divided into a hundred equal parts distinctly visible. If a fixed index be presented to this graduated circumference, the hundredth part of a revolution of the screw may be observed, by noting the passage of one division of the head under the index. Since one entire revolution of the head moves the point through the fiftieth of an...
Page 213 - Observer' at a salary of 100£ per annum, his duty being 'forthwith to apply himself with the most exact care and diligence to the rectifying the tables of the motions of the heavens and the places of the fixed stars, so as to find out the so much desired longitude of places for the perfecting the art of navigation.
Page 22 - The Latitude of a star is its angular distance from the ecliptic measured on a circle of latitude.
Page 13 - A sphere is a solid terminated by a curved surface all the points of which are equally distant from a point within called the centre.
Page 272 - The radial force, or that part of the disturbing force which acts in the direction of the line joining the centres of the sun and disturbed planet, has no effect on the areas, but is the cause of periodical changes of small extent in the distance of the planet from the sun. It has already been shown, that the force producing perfectly elliptical motion varies inversely as the square of the distance, and...
Page 13 - The radius of a sphere, is a straight line drawn from the center to any point of the surface.
Page 38 - Now, the arc of a circle, subtended by one second, is less than the 200,000th part of the radius, so that on a circle of 6 feet in diameter it would occupy no greater linear extent than part of an inch ; a quantity requiring a powerful microscope to be discerned at all.
Page 268 - But such a personification of "force" is a remnant of barbaric thought, in no wise sanctioned by physical science. When astronomy speaks of two planets as attracting each other with a " force " which varies directly as their masses and inversely as the squares of their distances...
Page 131 - It is, therefore, partly to this cause, and partly to those we have developed above, that the slight deviations we now perceive must be attributed. " Such is a summary of the hypothesis of La Place on the origin of the solar system. This hypothesis explains, in the most satisfactory manner, the three most remarkable phenomena presented by the planetary motions. " 1st. The motion of the planets in the same direction, and nearly in the same plane.