Practical Astronomy |
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Common terms and phrases
adjustment apparent noon astronomical axis azimuth celestial sphere Chronom chronometer error circle computed constant correction corresponding culmination declination denote determined difference division earth ecliptic elongation Ephemeris epoch Equal Altitudes equation equatorial star field of view formula geocentric give given Greenwich Greenwich mean Hence horizon-glass hour angle index-arm instant instrument latitude limb line of collimation longitude of perigee mean equinox mean sun measured meridian altitude meridian passage method micrometer micrometer head middle wire moon moon's motion observations orbit longitude parallax parallel pass perigee perpendicular pivots plane polar distance pole position prime vertical R. A. micrometer radius reading reduction refraction result reversed Right Ascension screw semi-diameter sextant sidereal clock sin² star star's station subtracting sun's mean place time-piece tion transit triangle true tude vernal equinox vertical zenith distance zenith telescope
Popular passages
Page 51 - If a ray of light suffers two successive reflections in the same plane by two plane mirrors, the angle between the first and last direction of the ray is twice the angle of the mirrors. D is set parallel to CX, and mirror C turns with arm B. The angle between SC and S...
Page 1 - Sun's co-ordinates, and other fundamental astronomical data, for equidistant intervals of Greenwich mean time. Part II, Ephemeris for the Meridian of Washington...
Page 1 - Ephemcris for the Meridian of Greenwich, gives the geocentric and heliocentric positions of the major planets, the Ephemeris of the Sun, and other fundamental astronomical data for equi-distant intervals of Greenwich mean time. Part II, Ephemeris...
Page 175 - Sli is less than the sum of the apparent semidiameters of the sun and moon. If, therefore, it appear that there will be an eclipse, we proceed thus to find its quantity, and the beginning and end. As we may suppose the motion to be uniform, QN : AB : : the time of describing NQ : the time of describing AB, which added to or subtracted from the time at A (according as the...
Page 171 - Mizar — the middle star in the " tail" of the Great Bear or handle of " the Plough" — appeared at times double, while on other occasions it was seen single and well defined. Other lines of the spectrum showed a similar variation. This doubling of the spectral lines was found to recur at regular intervals of about 52 days, thus indicating that the star was in reality a close...
Page 148 - ... take the difference between the PL of Diff. used and the one which follows it in the Ephemeris, (or, more strictly, half the difference of the preceding and following ones). With this difference, and the first correction of the Greenwich time already found, enter Table I...
Page 43 - The interval of time between two consecutive returns of the sun to the mean vernal equinox, called the mean tropical year, is according to Bessel 365.2422 mean solar days.
Page 43 - As the earth is rotating on its axis from west to east, the under current starting from the poles is constantly coming to a part moving faster than itself.
Page iii - ... Longitude on Land, explaining them concisely and deducing the requisite reductions formulae. Corrections for refraction, parallax, &c., also receive a good share in their respective places, while the instrumental errors are fully explained and discussed. Excellent illustrations of instruments (those in use in the Field and Permanent Observatories of the Military Academy during the summer encampment) are inserted and described. In addition to a set of tables collected together at the end, a few...
Page 161 - an average is of very little use, and would be as much too large in one case as too small in others ; while a series of units, as has been suggested, applicable to different sets of localities, would involve endless difficulties of inquiry and classification, would probably in the end produce rather an appearance than a reality of fairness.