|
Search over 100 encyclopedias and dictionaries: |
Research categories | Follow us on Twitter |
Research categories
View all topics in the newsView all reference sources at Encyclopedia.com |
|||
celestial sphere
celestial sphere An imaginary sphere of indefinite size, used as a background for assigning positional coordinates to celestial objects (see diagram). The sphere may be centred on the Earth, the observer, or any other point which acts as the origin of the chosen system of coordinates. As seen from Earth, the celestial sphere appears to rotate about the axis joining the celestial poles every 23 h 56 m 04 s (a sidereal day), actually a result of the axial spin of the Earth. Two important circles on the celestial sphere are the celestial equator and the ecliptic. The angle between them is about 23°.4, and is known as the obliquity of the ecliptic. The celestial equator and the ecliptic intersect at the vernal and autumnal equinoxes. The positions of the celestial poles, and hence of the celestial equator, are gradually moving on the celestial sphere because of a slow wobbling of the Earth in space termed precession. See also celestial coordinates.
|
|
|
Cite this article
"celestial sphere." A Dictionary of Astronomy. 1997. Encyclopedia.com. 26 May. 2012 <http://www.encyclopedia.com>. "celestial sphere." A Dictionary of Astronomy. 1997. Encyclopedia.com. (May 26, 2012). http://www.encyclopedia.com/doc/1O80-celestialsphere.html "celestial sphere." A Dictionary of Astronomy. 1997. Retrieved May 26, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O80-celestialsphere.html |
|
celestial sphere
celestial sphere, the imaginary sphere on to which the heavenly bodies appear to be projected. For astronomical work the radius of the celestial sphere is considered to be infinite. For some purposes the sun is regarded as occupying the central position, but for others the earth's centre or the observer's eye is considered to lie at the centre. Systems of great circles on the celestial sphere, particularly the horizon system, the equinoctial system, and the ecliptic system, have been devised to facilitate the solution of mathematical astronomical problems, especially those related to nautical astronomy. For illus. see ecliptic.
|
|
|
Cite this article
"celestial sphere." The Oxford Companion to Ships and the Sea. 2006. Encyclopedia.com. 26 May. 2012 <http://www.encyclopedia.com>. "celestial sphere." The Oxford Companion to Ships and the Sea. 2006. Encyclopedia.com. (May 26, 2012). http://www.encyclopedia.com/doc/1O225-celestialsphere.html "celestial sphere." The Oxford Companion to Ships and the Sea. 2006. Retrieved May 26, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O225-celestialsphere.html |
|
celestial sphere
celestial sphere imaginary sphere of infinite radius with the earth at its center. It is used for describing the positions and motions of stars and other objects. For these purposes, any astronomical object can be thought of as being located at the point where the line of sight from the earth through the object intersects the surface of the celestial sphere. In astronomical coordinate systems , the coordinate axes are great circles on the celestial sphere. In most systems of this type, the reference points are fixed on the sphere, so the two coordinates needed to locate a body are relatively constant. |
|
|
Cite this article
"celestial sphere." The Columbia Encyclopedia, 6th ed.. 2011. Encyclopedia.com. 26 May. 2012 <http://www.encyclopedia.com>. "celestial sphere." The Columbia Encyclopedia, 6th ed.. 2011. Encyclopedia.com. (May 26, 2012). http://www.encyclopedia.com/doc/1E1-celest-sph.html "celestial sphere." The Columbia Encyclopedia, 6th ed.. 2011. Retrieved May 26, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1E1-celest-sph.html |
|
celestial sphere
celestial sphere Imaginary sphere of infinite radius used to define the positions of celestial bodies as seen from Earth, the centre of the sphere. The sphere rotates, once in 24 hours, about a line that is an extension of the Earth's axis. The position of a celestial body is the point at which a radial line through it meets the surface of the sphere. The position is defined in terms of coordinates, such as declination and right ascension or altitude and azimuth, which refer to great circles on the sphere, such as the celestial equator or the ecliptic.
|
|
|
Cite this article
"celestial sphere." World Encyclopedia. 2005. Encyclopedia.com. 26 May. 2012 <http://www.encyclopedia.com>. "celestial sphere." World Encyclopedia. 2005. Encyclopedia.com. (May 26, 2012). http://www.encyclopedia.com/doc/1O142-celestialsphere.html "celestial sphere." World Encyclopedia. 2005. Retrieved May 26, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O142-celestialsphere.html |
|
celestial sphere
ce·les·tial sphere • n. an imaginary sphere of which the observer is the center and on which all celestial objects are considered to lie. |
|
|
Cite this article
"celestial sphere." The Oxford Pocket Dictionary of Current English. 2009. Encyclopedia.com. 26 May. 2012 <http://www.encyclopedia.com>. "celestial sphere." The Oxford Pocket Dictionary of Current English. 2009. Encyclopedia.com. (May 26, 2012). http://www.encyclopedia.com/doc/1O999-celestialsphere.html "celestial sphere." The Oxford Pocket Dictionary of Current English. 2009. Retrieved May 26, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O999-celestialsphere.html |
|
|
Search over 100 encyclopedias and dictionaries:
HighBeam™ Research, Inc. © Copyright 2012. All rights reserved.
The Encyclopedia.com advertising network includes:
