Celestial Sphere: The conceptualization of the infinite heavens as a sphere revolving around Earth, based upon the part of the skies visible from a point on Earth.

 

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Celestial Sphere: The apparent sphere of infinite radius having the earth as its center. All heavenly bodies (planets, stars, etc.) appear on the 'inner surface' of this sphere and the sun moves along the ecliptic.

Celestial Equator: The projection of the plane of the geographical equator upon the celestial sphere.

Asthenosphere: A portion of the upper mantle that is directly below the lithosphere. A zone of low strength in the upper mantle defines the top of the asthenosphere. This weak zone allows the plates of the . . . View Full Definition

Photosphere: The intensely bright portion of the sun visible to the unaided eye; the 'surface' of the sun. Reaching temperatures estimated at about 11,000°F, it is the portion of the sun's atmosphere wh . . . View Full Definition

Mesosphere: The layer of the atmosphere located between the stratosphere and the ionosphere, where temperatures drop rapidly with increasing height. It extends between 31 and 50 miles (17 to 80 kilomete . . . View Full Definition

Longitude, Celestial: The distance in degrees (arc) from 0° Aries eastward to any given point that intersects the ecliptic. Celestial longitude is measured from 0° to 360°. For example, 10° Taurus is expressed as . . . View Full Definition

Lithosphere: The solid, outer portion of the earth's crust coupled to the rigid upper mantle. Part of the geosphere.

Protective Atmosphere: A gas or vacuum envelope surrounding the workpieces, used to prevent or reduce the formation of oxides and other detrimental surface substances and to facilitate their removal.

Troposphere: The lowest layer of the atmosphere located between the earth's surface to approximately 11 miles (17 kilometers) into the atmosphere. Characterized by clouds and weather, temperature general . . . View Full Definition

Stratosphere: The layer of the atmosphere located between the troposphere and the mesosphere, characterized by a slight temperature increase and absence of clouds. It extends between 11 and 31 miles (17 t . . . View Full Definition