An Introduction to Practical Astronomy: With a Collection of Astronomical TablesHarper & Brothers, 1860 - 497 pages |
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Other editions - View all
An Introduction to Practical Astronomy and with a Collection of Astronomical ... Elias Loomis No preview available - 2015 |
An Introduction to Practical Astronomy: With a Collection of Astronomical Tables Elias Loomis No preview available - 2008 |
Common terms and phrases
altitude aperture apparent Aquarii astronomical Auriga axis azimuth Cambridge Camelopardi Cassiopeæ CATALOGUE OF 1500 Centauri centre Cephei chronometer clock coefficients collimation computed correction cosec Cygni determine diameter Diff difference Draconis earth eclipse emersion equal equation equatorial Eridani error eye-piece feet formula furnishes Greenwich Greenwich mean Hence Herculis horizontal parallax hour angle hour circle hourly motion Hydræ inches interval latitude Leonis limb Logarithms longitude Loomis's mean solar meridian Meridian circle micrometer Minoris moon's parallax Moon's true Nautical Almanac North Polar Dist object-glass Observatory observed obtain Ophiuchi Orionis parallax in right polar distance pole pole star position prime vertical radius refraction represent right ascension screw semi-diameter sidereal sine star star's declination sun and moon sun's Table tang Tauri telescope tion transit instrument triangle Trig Ursa Majoris values vertical wire zenith distance ΙΟ
Popular passages
Page 99 - ... to make the objects appear on the other wire ; if the contact still remains perfect, the axis of the telescope is in proper adjustment ; if not, it must be altered by moving the two screws which fasten, to the up-and-down piece, the collar into which the telescope screws. This adjustment is not very liable to be deranged.
Page 99 - ... the reading on the arc. Next place the index about the same quantity to the right of zero, or on the arc of excess, and make the contact of the two images perfect as before, and call the minutes and seconds on the arc of excess* the reading off the arc; and half the difference of these numbers is the index error; additive when the reading on the arc of excess is greater than that on the limb, and subtractive when the contrary is the case. EXAMPLE. .
Page 101 - At the same time, move the sextant slowly, making the axis of the telescope the centre of motion ; by which means the objects will pass each other, and the. contact be more...
Page 99 - ... to the left of zero, and looking towards the sun, the two images will appear either nearly in contact or overlapping each other; then perfect the contact, by moving the tangent-screw, and call the minutes and seconds denoted by the vernier, the reading on the arc. Next place the index about the same quantity to the right of zero, or on the arc of excess, and make the contact of the two images perfect as before, and call the minutes and seconds on the arc of excess* the reading off...
Page 141 - A cos 6 = cos a cos c + sin a sin c cos B cos c = cos a cos 6 + sin a sin 6 cos C Law of Cosines for Angles cos A = — cos B...
Page 48 - Direct the telescope to some small distant well-defined object, (the more distant the better,) and bisect it with the middle of the central vertical wire; then lift the telescope very carefully out of its angular bearings, or Y's, and replace it with the axis reversed ; point the telescope again to the same object, and if it be still bisected, the collimation adjustment is correct; if not, move the wires one half the error, by turning the small screws which hold the diaphragm near the eye-end of...
Page 121 - Astronomers, with a view of obtaining a convenient and uniform measure of time, have recourse to a mean solar day, the length of which is equal to the mean or average of all the apparent solar days in a year. An imaginary Sun, called the mean Sun...
Page 98 - ... be moved in a contrary direction to that which the object appears to take, in order to keep it in the field of view. Four dark glasses, of different depths of shade and color, are placed at K, between the index and horizon glasses ; also three more at N, any one or more of which can be turned down to moderate the intensity of the light, before reaching the eye, when a very luminous object (as the sun) is observed. The same purpose is effected by fixing a dark glass to the eye-end of the telescope:...
Page 98 - ... equal to the error itself; therefore, in modern instruments, there are seldom any means applied for its correction, it being considered preferable to determine its amount previous to observing or immediately after, and apply it with its proper sign to each observation. The amount of the index error may be found in the following manner; clamp the index at about 30...
Page 100 - ... telescope is used, the upper limb will appear as the lower, and vice versa ;* the angle shown on the instrument, when corrected for the index error, will be double the altitude of the sun's limb above the horizontal plane ; to the half of which, if the semi-diameter...