Elements of Plane AstronomyMilliken & Son, 1836 - 287 pages |
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Page 12
... less than 12 hours above the ho- rizon . When he is in the points of intersection of the ecliptic and equator , he is just 12 hours above the horizon , and it is then equal day and night . This latter circumstance takes place on the ...
... less than 12 hours above the ho- rizon . When he is in the points of intersection of the ecliptic and equator , he is just 12 hours above the horizon , and it is then equal day and night . This latter circumstance takes place on the ...
Page 22
... less this irradiation of light . We know certainly that some of the brighter fixed stars do not subtend an angle of 1 " , from the circumstance of their instantly disappearing , on the ap- proach of the dark edge of the moon . Dr ...
... less this irradiation of light . We know certainly that some of the brighter fixed stars do not subtend an angle of 1 " , from the circumstance of their instantly disappearing , on the ap- proach of the dark edge of the moon . Dr ...
Page 24
... less bright than Venus . Its colour was at first white and splendid , afterwards yellow , and in March , 1573 , red and fiery like Mars or Aldebaran , in May of a pale livid colour , and then became fainter and fainter till it vanished ...
... less bright than Venus . Its colour was at first white and splendid , afterwards yellow , and in March , 1573 , red and fiery like Mars or Aldebaran , in May of a pale livid colour , and then became fainter and fainter till it vanished ...
Page 25
... less bright than Y. A small star near & ursa majoris is now probably more bright than formerly , from the circumstance of its being named Alcor , an Arabic word which imports sharp - sightedness in the person who could see it . It is ...
... less bright than Y. A small star near & ursa majoris is now probably more bright than formerly , from the circumstance of its being named Alcor , an Arabic word which imports sharp - sightedness in the person who could see it . It is ...
Page 26
... less in brightness , and in the same field with the " above , was perfectly free from any such appearance . " Phil . Trans . 1791 . Dr. Herschel has , with unwearied attention , exerted himself in examining and noting every thing ...
... less in brightness , and in the same field with the " above , was perfectly free from any such appearance . " Phil . Trans . 1791 . Dr. Herschel has , with unwearied attention , exerted himself in examining and noting every thing ...
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Common terms and phrases
aberration accuracy altitude angular distance Aphelion apparent diameter apparent motion appear arch ascertained astronomical atmosphere axis azimuth called celestial bodies celestial pole centre circle circular clock comet computed concave surface conjunction declination deduced degree difference direction disc discovered diurnal diurnal motion earth eccentric anomaly ecliptic equal equator equatoreal equinox error fixed stars Georgium Sidus greater greatest Hence Herschel horizon hour inclination inferior conjunction inferior planets instrument interval Jupiter known latitude light lunar magnitude mean motion measured Mercury meridian method moon moon's move nearly node object observed obtained orbit parallax parallel passing Perihelion periodic perpendicular polar distance pole star quadrant quantity radius refraction revolve right angles right ascension satellites Saturn seen sextant shew shewn sidereal sine solar sphere spherical subtends sun's superior planets supposed tance telescope tion transit triangle tude velocity Venus vernier vertical visible whence zenith distance
Popular passages
Page 147 - ... the squares of the periodic times are as the cubes of the distances from the common centre, the centripetal forces will be inversely as the squares of the distances.
Page 236 - The third law, that the squares of the periodic times are as the cubes of the distances, is a property which belongs to the bodies describing elliptic orbits under the conditions just stated.
Page xix - It is shown in astronomy that the elevation of the celestial pole is equal to the latitude of the place, and...
Page 72 - The node through which the planet passes from the southern to the northern side of the ecliptic, is called the ascending node, and the other the descending node.
Page 8 - Declination is either north or south, according as the object is on the north or south side of the equator. North declination is generally regarded as positive, and south declination as negative.
Page 32 - Caille went to the Cape of Good Hope, for the express purpose of observing the southern hemisphere. 39. The knowledge of the spherical figure of the earth enables us readily to determine the position of the circles of the sphere, with respect to the horizon of any place, the latitude of which is known. For, ~ The altitude of the celestial pole at any place, is equal to the latitude of that place. Let SELNQ and HO (Fig. 5) be sections of the earth and horizon, in the plane of the meridian of the place...
Page 166 - Laplace has computed, that if it had been equal to the earth, it would have shortened the length of our year by ^ of a day. Now it has been perfectly ascertained, by the computations of Delambre on the Greenwich observations of the sun, that the length of the year has not been changed in consequence of the approach of that comet by any perceptible quantity, and thence Laplace has concluded that the mass of that comet is less than T^ of the mass of the earth.
Page 61 - The cause of this motion is shewn, by physical astronomy, to arise from the attraction of the sun and moon on the excess of matter at the equatoreal parts of the earth.
Page 172 - The phaenomena of a solar eclipse at a given place may be well understood by considering the apparent diameters of the sun and moon on the concave surface, and their distances as affected by parallax. When the apparent diameter of the sun is greater than that of the moon, the eclipse cannot be total, but it may be annular. From the tables we compute for the given place the time when the sun and moon are in conjunction, that is, have the same longitude. From the horizontal parallax of the moon, given...
Page 208 - What is the error of the best tables now in use ? hours, or one minute of space in two minutes of time. Therefore, if we make an error of one minute in observing the distance, we make an error of two minutes in time, or 30 miles of longitude at the equator. A single observation with the best sextant, may be liable to an error of more than half a minute ; but the accuracy of the result may be much increased by a mean of several observations taken to the east and west of the moon. The...