Difference between revisions of "Precession of the equinoxes"
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The '''precession of the equinoxes''' describes an astronomical phenomenon whereby the earth appears to wobble on its axis relative to the stars. This wobble is very slow, taking about 26,000 years to complete.<ref>[http://findarticles.com/p/articles/mi_m1134/is_10_115/ai_n16883025 "Turn, turn, turn: in addition to its daily spin and its annual trip around the Sun, the Earth wobblesaffecting the seasons, the "north star," and human history," ''Natural History'', 2006]</ref> The result of this is that the position of stars and [[constellation]]s overhead at any particular time gradually changes over the years. For example, the constellation that rises above the horizon at the spring [[equinox]] gradually cycles through the signs of the [[zodiac]] backwards. The star around which all the other stars seem to revolve (to an observer on Earth) also changes over time, meaning that Polaris, or the present North Star, has not always been the star closest to north, and will be replaced by other stars in the future. The Earth's axis pointed to the star Thuban in the year 3000 B.C., and it will point to the bright star Vega in the year A.D. 14,000. <ref>[http://www.essortment.com/all/northstarastro_rmdz.htm "What is the north star?" ''Essortment.com'']</ref> | The '''precession of the equinoxes''' describes an astronomical phenomenon whereby the earth appears to wobble on its axis relative to the stars. This wobble is very slow, taking about 26,000 years to complete.<ref>[http://findarticles.com/p/articles/mi_m1134/is_10_115/ai_n16883025 "Turn, turn, turn: in addition to its daily spin and its annual trip around the Sun, the Earth wobblesaffecting the seasons, the "north star," and human history," ''Natural History'', 2006]</ref> The result of this is that the position of stars and [[constellation]]s overhead at any particular time gradually changes over the years. For example, the constellation that rises above the horizon at the spring [[equinox]] gradually cycles through the signs of the [[zodiac]] backwards. The star around which all the other stars seem to revolve (to an observer on Earth) also changes over time, meaning that Polaris, or the present North Star, has not always been the star closest to north, and will be replaced by other stars in the future. The Earth's axis pointed to the star Thuban in the year 3000 B.C., and it will point to the bright star Vega in the year A.D. 14,000. <ref>[http://www.essortment.com/all/northstarastro_rmdz.htm "What is the north star?" ''Essortment.com'']</ref> | ||
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| + | ==List of selected North Stars<ref>http://www.glyphweb.com/esky/concepts/northerncelestialpole.html</ref>== | ||
| + | {| class="wikitable" | ||
| + | |- | ||
| + | !Approximate year | ||
| + | !Common name | ||
| + | !Astronomical name | ||
| + | |- | ||
| + | |3000 BC | ||
| + | |[[Thuban]] | ||
| + | |Alpha [[Draco]]nis | ||
| + | |- | ||
| + | |1000 BC | ||
| + | |[[Kochab]] | ||
| + | |Beta [[Ursa Minor]]is | ||
| + | |- | ||
| + | |2000 AD | ||
| + | |[[Polaris]] | ||
| + | |Alpha [[Ursa Minor]]is | ||
| + | |- | ||
| + | |4000 AD | ||
| + | |[[Alrai]] | ||
| + | |Gamma [[Cepheus|Cephei]] | ||
| + | |- | ||
| + | |7500 AD | ||
| + | |[[Alderamin]] | ||
| + | |Alpha [[Cepheus|Cephei]] | ||
| + | |- | ||
| + | |14000 AD | ||
| + | |[[Vega]] | ||
| + | |Alpha [[Lyra]]e | ||
| + | |} | ||
== References == | == References == | ||
Revision as of 21:24, December 1, 2009
The precession of the equinoxes describes an astronomical phenomenon whereby the earth appears to wobble on its axis relative to the stars. This wobble is very slow, taking about 26,000 years to complete.[1] The result of this is that the position of stars and constellations overhead at any particular time gradually changes over the years. For example, the constellation that rises above the horizon at the spring equinox gradually cycles through the signs of the zodiac backwards. The star around which all the other stars seem to revolve (to an observer on Earth) also changes over time, meaning that Polaris, or the present North Star, has not always been the star closest to north, and will be replaced by other stars in the future. The Earth's axis pointed to the star Thuban in the year 3000 B.C., and it will point to the bright star Vega in the year A.D. 14,000. [2]
List of selected North Stars[3]
| Approximate year | Common name | Astronomical name |
|---|---|---|
| 3000 BC | Thuban | Alpha Draconis |
| 1000 BC | Kochab | Beta Ursa Minoris |
| 2000 AD | Polaris | Alpha Ursa Minoris |
| 4000 AD | Alrai | Gamma Cephei |
| 7500 AD | Alderamin | Alpha Cephei |
| 14000 AD | Vega | Alpha Lyrae |