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vertical circle
(Encyclopedia)vertical circle, in astronomy, the great circle on the celestial sphere that passes from the observer's zenith through a given celestial body. In the altazimuth coordinate system the altitude of a bod...equinox
(Encyclopedia)equinox ēˈkwĭnŏks [key], either of two points on the celestial sphere where the ecliptic and the celestial equator intersect. The vernal equinox, also known as “the first point of Aries,” is t...sphere of influence
(Encyclopedia)sphere of influence, term formerly applied to an area over which an outside power claims hegemony with the intention of subsequently gaining more definite control, as in colonization, or with the inte...zenith
(Encyclopedia)zenith, in astronomy, the point in the sky directly overhead; more precisely, it is the point at which the celestial sphere is intersected by an upward extension of a plumb line from the observer's lo...hour circle
(Encyclopedia)hour circle, in astronomy, a secondary axis in the equatorial coordinate system. The hour circle of a celestial body is the great circle on the celestial sphere that passes through both the body and t...equator
(Encyclopedia)equator, imaginary great circle around the earth, everywhere equidistant from the two geographical poles and forming the base line from which latitude is reckoned. The equator, which measures c.24,902...diurnal circle
(Encyclopedia)diurnal circle dīûrˈnəl [key], apparent path followed by a star due to the earth's rotation on its axis. The stars appear to move on the celestial sphere in concentric circular paths centered at t...altazimuth coordinate system
(Encyclopedia)altazimuth coordinate system ăltăzˈəməth [key] or horizon coordinate system, astronomical coordinate system in which the position of a body on the celestial sphere is described relative to an obs...globe
(Encyclopedia)globe, spherical map of the earth (terrestrial globe) or the sky (celestial globe). The terrestrial globe provides the only graphic representation of the areas of the earth without significant distort...nadir
(Encyclopedia)nadir nāˈdər [key] [Arab.,=opposite], in astronomy, the point on the celestial sphere directly opposite the zenith, i.e., directly beneath the observer. ...Browse by Subject
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