Plane of the ecliptic
The plane of the ecliptic (also known as the ecliptic plane) is the plane of the Earth's orbit around the Sun.[1] It is the primary reference plane when describing the position of bodies in the Solar System,[2] with celestial latitude being measured relative to the ecliptic plane.[3] In the course of a year, the Sun's apparent path through the sky lies in this plane. The planetary bodies of our Solar System all tend to lie near this plane, since they were formed from the Sun's spinning, flattened, protoplanetary disk.[1]
The ecliptic plane was so named because a solar eclipse can only occur when the Moon crosses this plane. Its position changes over time, so must be accompanied by an epoch, usually defined as 1950.0 or 2000.0.[4] The ecliptic plane and the celestial equator intersect each other in two diametrical imaginary points called the vernal and autumnal equinoxes.[5] As of 2005, it is at an angle of 23°27’ to the celestial equator,[3][6][7] while the inclination of the lunar orbit is approximately five degrees and nine minutes.[7]
By definition, the plane of the ecliptic and the plane of Earth's orbit are the same,[8] and are not fixed or constant.[9] The position of the plane of the ecliptic relative to the invariable plane is altered by gravitational perturbations of the other planets, thus changing the celestial ecliptic and the pole of the ecliptic.[9] The latitude of the stars also change, as the plane of the ecliptic varies in degrees.[9] The positions of stars may be defined relative to either the plane of the ecliptic or the plane of the Earth's equator.[10]
Earth's axial tilt is constant relative to the invariable plane, that is, relative to inertial space (precession does not change the tilt)—it changes because the ecliptic moves as much as three degrees relative to the invariable plane over tens of thousands of years.
[edit] References
- ^ a b "Astronomy Picture of the Day". NASA. September 21, 1996. http://apod.nasa.gov/apod/ap960921.html. Retrieved 2009-05-09.
- ^ "Definition of "ecliptic plane"". Heavens Above. DLR/GSOC. http://www.heavens-above.com/glossary.aspx?lat=0&lng=0&alt=&loc=&TZ=GMT&term=ecliptic+plane. Retrieved 2009-05-09.
- ^ a b "Ecliptic". Encarta. Microsoft. 2005.
- ^ Weisstein, Eric; Ed Post (1996–2007). "Ecliptic Plane". Wolfram Research. http://scienceworld.wolfram.com/astronomy/EclipticPlane.html. Retrieved 2009-05-09.
- ^ Motz, Lloyd; Weaver, Jefferson Hane (1995). The story of astronomy. Da Capo Press. ISBN 0306450909.
- ^ Leonard, Levi Washburn; Platts, John (1831). The Literary and Scientific Class Book. J. and J.W. Prentiss.
- ^ a b Ritchie, Archibald Tucker (1850). The Dynamical Theory of the Formation of the Earth. Longman, Brown, Green and Longmans.
- ^ Taylor, Robert (1825). A key to the knowledge of nature. Baldwin, Cradock, and Joy.
- ^ a b c Drayson, Alfred Wilks (1873). On the Cause, Date, and Duration of the Last Glacial Epoch of Geology, and the Probable Antiquity of Man. Chapman & Hall.
- ^ Nature Published by Macmillan Journals ltd., 1891, page 9 (accessed April, 2009)
[edit] Further reading
- Laplace, Pierre Simon (1830). The System of the World. Translator: Henry Hickman Harte. Dublin University Press. pp. 383. http://books.google.com/books?id=TZAEAAAAYAAJ&pg=PA383&dq=%22Plane+of+ecliptic%22. Retrieved 10 May 2009.
