hour-circlen.
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.
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the world > the universe > celestial sphere > circle of celestial sphere > [noun] > great circle > hour circle
hour-circle1690
1690 W. Leybourn Cursus mathematicus 359 Through either of the Poles..there are drawn 12 Meridians or hour-Circles.
1815 J. Smith Panorama Sci. & 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.
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the world > the earth > earth sciences > geography > map-making > map > [noun] > globe > fitments
quadrant of altitude1581
hour-wheel1594
hour-circle1674
1674 J. Moxon Tutor to Astron. & Geogr. (ed. 3) i. 6 The Hour Circle is a small Brasen Circle, fitted on the Meridian whose Center is the Pole of the world.
1674 J. Moxon Tutor to Astron. & Geogr. (ed. 3) 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.
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the world > the universe > cosmology > science of observation > astronomical instruments > observational instruments > [noun] > telescope > part of
rete1665
field lens1817
hour-circle1837
seeker1892
1837 Penny Cycl. IX. 486 The hour-circle is made to read oh, when the telescope is in the meridian of the place.
1861 G. F. Chambers Handbk. Descr. Astron. VIII. iii. 339 The hour circle has a milled edge in which the threads of an endless screw..are arranged to work so as to give a slow motion in right ascension.
This entry has not yet been fully updated (first published 1899; most recently modified version published online September 2021).
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