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| {{Refimprove|date=January 2010}}
| | Alyson is what my spouse enjoys to contact me but I don't like when individuals use my complete title. Office supervising is my profession. To play lacross is the thing I love most of all. For a whilst I've been in Alaska but I will have to transfer in a year or two.<br><br>Also visit my weblog - email psychic readings ([http://www.atvriders.tv/uprofile.php?UID=257285 atvriders.tv]) |
| [[Image:Heliocentric.jpg|thumb|250px|right|Heliocentric Solar System]]
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| In [[astronomy]], the '''Earth's [[orbit]]''' is the motion of the [[Earth]] around the [[Sun]], from an average [[List of Solar System objects in hydrostatic equilibrium#Planets|distance]] of [[Astronomical unit|149.59787 million kilometers]] away. A complete orbit of the earth around the Sun occurs every 365.2563666 mean solar days ([[sidereal year|1 sidereal year]]).<ref group=nb>A solar day (one rotation relative to the Sun) is on average 24 hours; it takes 365.256363 of these to orbit the Sun once in the sense of returning to the same position relative to the stars. Such an orbit relative to the stars is called a sidereal year.</ref> This motion gives an apparent movement of the Sun with respect to the stars at a rate of about 1°/day (or a Sun or Moon diameter every 12 hours) eastward, as seen from Earth. On average it takes 24 hours—a [[Solar time|solar day]]—for Earth to complete a full rotation about its axis relative to the Sun so that the Sun returns to the [[Meridian (astronomy)|meridian]]. The [[orbital speed]] of the Earth around the Sun averages about 30 km/s (108,000 km/h), which is fast enough to cover the planet's diameter (about 12,700 km) in seven minutes, and the distance to the [[Moon]] of 384,000 km in four hours.<ref name="earth_fact_sheet">{{cite web|last=Williams|first=David R.|date=2004-09-01|url=http://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html|title=Earth Fact Sheet|publisher=NASA|accessdate=2007-03-17}}</ref>
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| Viewed from a vantage point above the north poles of both the Sun and the Earth, the Earth would appear to revolve in a counterclockwise direction about the Sun. From the same vantage point both the Earth and the Sun would appear to rotate in a counterclockwise direction about their respective axes.
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| ==Distance covered in an orbit==
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| Approximating Earth's orbit around the sun to be circular, the distance Earth travels in one year is roughly 940 million kilometers (585 million miles).
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| ==History of study==
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| {{main|Heliocentrism}}
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| [[Image:geoz wb en.svg|thumb|250px|right|Heliocentrism (lower panel) in comparison to the geocentric model (upper panel)]]
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| Heliocentrism is the scientific model which places the Sun at the center of the [[Solar System]]. Historically, heliocentrism is opposed to [[geocentrism]], which placed the earth at the center. In the 16th century, [[Nicolaus Copernicus]]' ''[[De revolutionibus]]'' presented a full discussion of a [[Copernican heliocentrism|heliocentric model]] of the universe in much the same way as [[Ptolemy]]'s ''[[Almagest]]'' had presented his geocentric model in the 2nd century. This '[[Copernican revolution]]' resolved the issue of planetary [[apparent retrograde motion|retrograde motion]] by arguing that such motion was only perceived and apparent, rather than real...
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| ==Influence on the Earth==
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| {{main|Season}}
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| Because of the [[axial tilt]] of the Earth (often known as the obliquity of the ecliptic), the inclination of the Sun's trajectory in the sky (as seen by an observer on Earth's surface) varies over the course of the year. For an observer at a northern latitude, when the northern pole is tilted toward the Sun the day lasts longer and the Sun appears higher in the sky. This results in warmer average temperatures from the increase in solar radiation reaching the surface. When the northern pole is tilted away from the Sun, the reverse is true and the climate is generally cooler. Above the [[Arctic Circle]], an extreme case is reached where there is no daylight at all for part of the year. (This is called a [[polar night]].) This variation in the climate (because of the direction of the Earth's axial tilt) results in the [[season]]s.
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| ==Events in the orbit==
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| By one astronomical convention, the four seasons are determined by flanges, the [[solstice]]s—the point in the orbit of maximum axial tilt toward or away from the Sun—and the [[equinox]]es, when the direction of the tilt and the direction to the Sun are perpendicular. In the northern hemisphere winter solstice occurs on about December 21, summer solstice is near June 21, spring equinox is around March 20 and autumnal equinox is about September 23. The axial tilt in the southern hemisphere is exactly the opposite of the direction in the northern hemisphere. Thus the seasonal effects in the south are reversed.
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| In modern times, Earth's [[perihelion]] occurs around January 3, and the [[aphelion]] around July 4 (for other eras, see [[precession (astronomy)|precession]] and [[Milankovitch cycles]]). The changing Earth-Sun distance results in an increase of about 6.9%<ref>Aphelion is 103.4% of the distance to perihelion. Due to the inverse square law, the radiation at perihelion is about 106.9% the energy at aphelion.{{citation needed|date=January 2010}}</ref> in solar energy reaching the Earth at perihelion relative to aphelion. Since the southern hemisphere is tilted toward the Sun at about the same time that the Earth reaches the closest approach to the Sun, the southern hemisphere receives slightly more energy from the Sun than does the northern over the course of a year. However, this effect is much less significant than the total energy change due to the axial tilt, and most of the excess energy is absorbed by the higher proportion of water in the southern hemisphere.<ref>{{cite web|last=Williams|first=Jack|date=2005-12-20|url=http://www.usatoday.com/weather/tg/wseason/wseason.htm|title=Earth's tilt creates seasons|publisher=USAToday|accessdate=2007-03-17}}</ref>
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| The [[Hill sphere]] ([[gravity|gravitational]] sphere of influence) of the Earth is about 1.5 Gm (or 1,500,000 [[kilometer]]s) in radius.<ref>{{cite web|author=Vázquez, M.; Montañés Rodríguez, P.; Palle, E.|year=2006|url= http://www.iac.es/folleto/research/preprints/files/PP06024.pdf|format=PDF|title=The Earth as an Object of Astrophysical Interest in the Search for Extrasolar Planets|publisher=Instituto de Astrofísica de Canarias|accessdate=2007-03-21}}</ref><ref group="nb">For the Earth, the Hill radius is
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| :<math>\begin{smallmatrix} R_H = a\left ( \frac{m}{3M} \right )^{\frac{1}{3}} \end{smallmatrix}</math>,
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| where ''m'' is the mass of the Earth, ''a'' is an Astronomical Unit, and ''M'' is the mass of the Sun. So the radius in A.U. is about:
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| <math>\begin{smallmatrix} \left ( \frac{1}{3 \cdot 332,946} \right )^{\frac{1}{3}} = 0.01 \end{smallmatrix}</math>.{{citation needed|date=January 2010}}</ref> This is the maximum distance at which the Earth's gravitational influence is stronger than the more distant Sun and planets. Objects orbiting the Earth must be within this radius, otherwise they can become unbound by the gravitational perturbation of the Sun.
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| <center>Orbital Characteristics
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| <div>
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| {| border = "1"
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| | [[Epoch (astronomy)|epoch]]
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| | [[J2000.0]]<ref group=nb name=epoch/>
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| | [[Apsis|aphelion]]
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| | {{convert|152098232|km}}<br> 1.01671388 [[astronomical unit|AU]]<ref group=nb name=apsis/>
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| | [[Apsis|perihelion]]
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| | {{convert|147098290|km}}<br> 0.98329134 AU<ref group=nb name=apsis/>
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| | [[Semi-major axis|semimajor axis]]
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| | {{convert|149598261|km}}<br> 1.00000261 AU<ref name=standish_williams_iau/>
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| | [[Orbital eccentricity|eccentricity]]
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| | 0.01671123<ref name=standish_williams_iau/>
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| | [[inclination]]
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| | 7.155° to [[Sun]]'s [[equator]]<br>1.578690°<ref name=Allen294/> to [[invariable plane]]
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| | [[longitude of the ascending node]]
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| | 348.73936°<ref name="earth_fact_sheet"/><ref group=nb name=asc_node/>
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| | [[argument of periapsis]]
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| | 114.20783°<ref name="earth_fact_sheet"/><ref group=nb name=arg_peri/>
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| | [[Orbital period|period]]
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| | 365.256363004 days<ref name="IERS"/><br>1.000017421 [[Julian year (astronomy)|yr]]
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| | [[Orbital speed|average speed]]
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| | {{convert|29.78|km/s}}<ref name="earth_fact_sheet"/><br>{{convert|107200|km/h}}
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| |}</div></center>
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| The following diagram shows the relation between the line of solstice and the line of [[apsides]] of Earth's elliptical orbit. The orbital ellipse (with eccentricity exaggerated for effect) goes through each of the six Earth images, which are sequentially the [[apsis#Earth's perihelion and aphelion|perihelion]] (periapsis—nearest point to the Sun) on anywhere from 2 January to 5 January, the point of March [[equinox]] on 20 or 21 March, the point of June [[solstice]] on 20 or 21 June, the [[apsis#Earth's perihelion and aphelion|aphelion]] (apoapsis—farthest point from the Sun) on anywhere from 4 July to 7 July, the September equinox on 22 or 23 September, and the December solstice on 21 or 22 December. Note that the diagram shows an exaggerated representation of the shape of Earth's orbit. In reality, the actual path of Earth's orbit is not as eccentric as that portrayed in the diagram.
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| [[Image:Seasons1.svg|center|600px]]
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| Due to the revolution and position of Earth in orbit the maximum intensity of sun rays will hit the earth slightly north of equator in June Solstice and thus called as the '''[[Tropic of Cancer]]''' and the maximum intensity of sun rays will hit the earth slightly south of equator in December Solstice called as '''[[Tropic of Capricorn]]'''.
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| ==Future==
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| {{main|Stability of the solar system}}
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| Mathematicians and astronomers (such as [[Laplace]], [[Joseph Louis Lagrange|Lagrange]], [[Gauss]], [[Henri Poincaré|Poincaré]], [[Kolmogorov]], [[Vladimir Arnold]], and [[Jürgen Moser]]) have searched for evidence for the stability of the planetary motions, and this quest led to many mathematical developments, and several successive 'proofs' of stability for the solar system.<ref>{{cite encyclopedia|encyclopedia=Encyclopedia of Astronomy and Astropvhysics|editor-last=Murdin |editor-first=Paul|id=article 2198|url=http://eaa.iop.org/abstract/0333750888/2198|last=Laskar|first=J.|title=Solar System: Stability|year=2001|publisher=Institute of Physics Publishing|location=Bristol}}</ref> By most predictions, Earth's orbit will be relatively stable over long periods.<ref>{{cite book|last=Gribbin|first=John|title=Deep simplicity : bringing order to chaos and complexity|year=2004|publisher=Random House|location=New York|isbn=978-1-4000-6256-0|edition=1st U.S.}}</ref>
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| In 1989, [[Jacques Laskar]]'s work showed that the Earth's orbit (as well as the orbits of all the inner planets) is chaotic and that an error as small as 15 metres in measuring the initial position of the Earth today would make it impossible to predict where the Earth would be in its orbit in just over 100 million years' time. Modeling the solar system is subject to the [[n-body problem]].
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| The angle of the Earth's tilt is relatively stable over long periods. However, the tilt does undergo a slight, irregular motion (known as [[nutation]]) with a main period of 18.6 years. The orientation (rather than the angle) of the Earth's axis also changes over time, [[precession|precessing]] around in a complete circle over each 25,800 year cycle; this precession is the reason for the difference between a sidereal year and a [[tropical year]]. Both of these motions are caused by the varying attraction of the Sun and Moon on the Earth's [[equatorial bulge]]. From the perspective of the Earth, the poles also migrate a few meters across the surface. This [[polar motion]] has multiple, cyclical components, which collectively are termed [[quasiperiodic motion]]. In addition to an annual component to this motion, there is a 14-month cycle called the [[Chandler wobble]]. The rotational velocity of the Earth also varies in a phenomenon known as [[length-of-day variation]].<ref>{{cite web|last=Fisher|first=Rick|date=1996-02-05|url=http://www.cv.nrao.edu/~rfisher/Ephemerides/earth_rot.html|title=Earth Rotation and Equatorial Coordinates|publisher=National Radio Astronomy Observatory|accessdate= 2007-03-21}}</ref>
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| ==See also==
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| *[[Barycentric coordinates (astronomy)]]
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| *[[Earth's rotation]]
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| *[[Geocentric orbit]] – the orbit of any object orbiting the Earth, such as the Moon or an artificial satellite
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| *[[Satellites]]
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| *[[Space station]]
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| ==Notes==
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| {{reflist|group=nb|refs=
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| <ref name=apsis>aphelion = ''a'' × (1 + ''e''); perihelion = ''a'' × (1 – ''e''), where ''a'' is the semi-major axis and ''e'' is the eccentricity.</ref>
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| <ref name=epoch>All astronomical quantities vary, both [[Secular phenomena|secularly]] and [[Frequency|periodically]]. The quantities given are the values at the instant [[J2000.0]] of the secular variation, ignoring all periodic variations.</ref>
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| <ref name=asc_node>The reference lists the longitude of the ascending node as −11.26064°, which is equivalent to 348.73936° by the fact that any angle is equal to itself plus 360°.</ref>
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| <ref name=arg_peri>The reference lists the [[longitude of periapsis|longitude of perihelion]], which is the sum of the longitude of the ascending node and the argument of perihelion. That is, 114.20783° + (−11.26064°) = 102.94719°.</ref>
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| }}
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| ==References==
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| {{Reflist|refs=
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| <ref name=standish_williams_iau>{{cite web | author=Standish, E. Myles; Williams, James C | title=Orbital Ephemerides of the Sun, Moon, and Planets | publisher=International Astronomical Union Commission 4: (Ephemerides) | url=http://iau-comm4.jpl.nasa.gov/XSChap8.pdf | format=PDF | accessdate=2010-04-03 }} See table 8.10.2. Calculation based upon 1 AU = 149,597,870,700(3) m.</ref>
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| <ref name=Allen294>{{cite book | title=Allen's Astrophysical Quantities | author=Allen, Clabon Walter; Cox, Arthur N. | publisher=Springer | year=2000 | isbn=0-387-98746-0 | url=http://books.google.com/?id=w8PK2XFLLH8C&pg=PA294 | page=294}}</ref>
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| <ref name=IERS>{{cite web | author=Staff | date=2007-08-07 | url=http://hpiers.obspm.fr/eop-pc/models/constants.html | title=Useful Constants | publisher=[[International Earth Rotation and Reference Systems Service]]| accessdate=2008-09-23 }}</ref>
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| }}
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| {{orbits}}
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| {{DEFAULTSORT:Earth's Orbit}}
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| [[Category:Earth]]
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| [[Category:Dynamics of the Solar System]]
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| [[tr:Dünya'nın yörüngesi]]
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Alyson is what my spouse enjoys to contact me but I don't like when individuals use my complete title. Office supervising is my profession. To play lacross is the thing I love most of all. For a whilst I've been in Alaska but I will have to transfer in a year or two.
Also visit my weblog - email psychic readings (atvriders.tv)