| 释义 |
ˈhour-circle
1. Any great circle of the celestial sphere passing through the poles; a meridian or declination-circle. Twenty-four of these are commonly marked on the globe, each distant from the next by one hour of right ascension.
1690Leybourn Curs. Math. 359 Through either of the Poles..there are drawn 12 Meridians or hour-Circles. 1812–16J. Smith Panorama Sc. & Art I. 518 Twenty-four of these circles of declination are called hour-circles.
2. A small brass circle at the north pole of an artificial globe, graduated into hours and divisions of an hour.
1674Moxon Tutor Astron. i. (ed. 3) 6 The Hour Circle is a small Brasen Circle, fitted on the Meridian whose Center is the Pole of the world. Ibid. iii. 119 Turn about the Globe till the Index of the Hour Circle points to the Hour of the Day or Night.
3. A graduated circle upon an equatorial telescope, parallel to the plane of the equator, by means of which the hour-angle of a star is observed.
1837Penny Cycl. IX. 486 (s.v. Equatorial) The hour-circle is made to read oh, when the telescope is in the meridian of the place. 1877G. F. Chambers Astron. vii. iii. (ed. 3) 650 The hour-circle has a female screw cut on its outer edge, in which an endless screw..is arranged to work so as to give a slow motion in Right Ascension. |