The Celestial - celestial meridian We will introduce...

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The Celestial Sphere Much of our initial discussion of Astronomy will concern the motion of objects in the sky. Therefore, we shall introduce some terminology and a coordinate system that allow us to specify succinctly the location of particular objects in the heavens. For a more extensive discussion, see Astronomy without a Telescope . The Celestial Sphere It is useful in discussing objects in the sky to imagine them to be attached to a sphere surrounding the earth. This fictitious construction is called the celestial sphere . At any one time we see no more than half of this sphere, but we will refer loosely to the imaginary half-sphere over our heads as just the celestial sphere (see adjacent figure). The point on the celestial sphere that is directly over our heads at a given time is termed the zenith . The imaginary circle passing through the North and South points on our horizon and through the zenith is termed the
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Unformatted text preview: celestial meridian . We will introduce additional terminology associated with the celestial sphere later. Celestial Coordinate Systems We can define a useful coordinate system for locating objects on the celestial sphere by projecting onto the sky the latitude-longitude coordinate system that we use on the surface of the earth. As illustrated in the adjacent figure, this allows us to define "North and South Celestial Poles" (the imaginary points about which the diurnal motion appears to take place) and a "Celestial Equator". The figure illustrates that these imaginary objects are the exact analogs of the corresponding imaginary objects on the surface of the earth. Thus, we shall be able to specify the precise location of things on the celestial sphere by giving the celestial analog of their latitudes and longtitudes, or something related to those quantities....
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