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According to [[International Astronomical Union]] (IAU), a '''planet''' is a celestial body [[orbit]]ing a [[star]] or [[Stellar evolution#Stellar remnants|stellar remnant]] that is massive enough to be rounded by its own [[gravity]] (but not massive enough to cause [[thermonuclear fusion]] in its inner core), and has [[cleared the neighbourhood|cleared its neighbouring region]] of [[planetesimal]]s. <ref name=IAU>{{ cite web | title = IAU 2006 General Assembly: Result of the IAU Resolution votes | url = http://www.iau2006.org/mirror/www.iau.org/iau0603/index.html | year = 2006 | accessdate = 2007-04-30 }}</ref> <ref name=WSGESP>{{ cite web |year = 2001 | title = Working Group on Extrasolar Planets (WGESP) of the International Astronomical Union | work = IAU | url = http://www.dtm.ciw.edu/boss/definition.html | accessdate = 2006-05-25 }}</ref> There are eight bodies in the Solar Sysytem that meet this definition: [[Mercury]], [[Venus]], [[Earth]], [[Mars]], [[Jupiter]], [[Saturn]], [[Uranus]] and [[Neptune]].
According to the [[International Astronomical Union]] (IAU), a '''planet''' is a celestial body [[orbit]]ing a [[star]] or [[Stellar evolution#Stellar remnants|stellar remnant]] that is massive enough to be rounded by its own [[gravity]] (but not massive enough to cause [[thermonuclear fusion]] in its inner core), and has [[cleared the neighbourhood|cleared its neighbouring region]] of [[planetesimal]]s. <ref name=IAU>{{ cite web | title = IAU 2006 General Assembly: Result of the IAU Resolution votes | url = http://www.iau2006.org/mirror/www.iau.org/iau0603/index.html | year = 2006 | accessdate = 2007-04-30 }}</ref> <ref name=WSGESP>{{ cite web |year = 2001 | title = Working Group on Extrasolar Planets (WGESP) of the International Astronomical Union | work = IAU | url = http://www.dtm.ciw.edu/boss/definition.html | accessdate = 2006-05-25 }}</ref> There are eight bodies in the Solar Sysytem that meet this definition: [[Mercury]], [[Venus]], [[Earth]], [[Mars]], [[Jupiter]], [[Saturn]], [[Uranus]] and [[Neptune]].


Again, according to that definition, bodies that don't obey the third condition, that is, orbiting the [[Sun]], rounded by its own gravity but not cleared the neighbourhood, is called '''[[dwarf planet]]'''. One of them is [[Pluto]], which is former considered as a planet. Other bodies that orbiting the Sun are generically called '''[[Small bodies of Solar System]]'''.  
Bodies that orbit the sun and are rounded by their own gravity, but have not cleared the neighbourhood, are called "[[dwarf planet]]s." One of them is [[Pluto]], which was formerly considered a planet. Other bodies orbiting the Sun are generically called "[[small bodies of the Solar System]]."


Another related term is '''[[exoplanet]]'''. Although there are no official defition for this term, it is often used to indicate bodies analogue to the planets, but that orbites other [[star]]s that not the Sun.<ref name=exoplanet>{{ cite web |url = http://exoplanets.org/}}</ref>
Another related term is "[[exoplanet]]." Although there is no official defition for this term, it is often used to indicate bodies analogous to the planets, but that orbit stars other than the Sun.<ref name=exoplanet>{{ cite web |url = http://exoplanets.org/}}</ref>


==The Planets==
==The Planets==
The planets can be subdivided into two main groups. The inner 4 terrestrial planets have a rocky composition. They are relatively small in size. The outer 4 planets are known as Gas Giants and have a thick gaseous atmospheres. Some physical information is followed:
The planets can be subdivided into two main groups. The inner 4 terrestrial planets have a rocky composition. They are relatively small in size. The outer 4 planets are known as Gas Giants and have a thick gaseous atmospheres.  
 
==Table of the Planets==


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==Etimology and History==
==Etymology and History==
 
The word "planet" came from the greek πλανήτ- (''planēt-''), meaning "wanderers." Before the invention of the telescope, there were seven planets visible in the sky; the ancient Greeks considered each one to be dedicated to a deity:


The word "planet" came from the greek πλανήτ- (''planēt-''), meaning "wanderers". There was, then, seven planets in the Sky, each one dedicated to a greek deitiy:
*''Phainon'', "the shiner," dedicated to [[Cronos]];
*''Phainon'', the shiner, dedicated to [[Cronus]];
*''Phaethon'', also meaning "shining," brighter than the first, dedicated to [[Zeus]];
*''Phaethon'', brighter the first and below it, dedicated to [[Zeus]];
*''Pyroeis'', "fiery", the red one, dedicated to [[Ares]];
*''Pyroeis'', "fiery", the red one, dedicated to [[Ares]];
*''Phosphoros'', "light bringer", the brightest one, dedicated to [[Aphrodite]];
*''Phosphoros'', "light bringer", the brightest one, dedicated to [[Aphrodite]];
*''Stilbon'', the gleamer, dedicated to [[Hermes]]; <ref name=planet_greek_names>{{cite book|title=The History and Practice of Ancient Astronomy|author=James Evans|publisher=Oxford University Press|year=1998|pages=296-7}}</ref>
*''Stilbon'', the "gleamer," dedicated to [[Hermes]]; <ref name=planet_greek_names>{{cite book|title=The History and Practice of Ancient Astronomy|author=James Evans|publisher=Oxford University Press|year=1998|pages=296-7}}</ref>
added by our [[Sun]] and [[Moon]], the bigest wanderers in the sky. Later, n the time of the [[philosophy|philosophers]], many models of universe was created, which the most famous for us is the [[Aristotelian universe | Aristotle's one]]. In his system, the planets belong each one to one cristaline sphere, concentric to the others. Inner the seven planet's sphere stay the material shperes (''grosso modo'', the Earth); Outer them, the ''shpere of fixed stars''.
as well as the [[Sun]] and Earth's [[Moon]], the biggest wanderers in the sky. [[philosophy|Philosophers]] in antiquity created many models of the universe, of which the best-known is [[Aristotelian universe | Aristotle's]]. In his system, each planet belongs to one crystalline sphere, concentric with the others. Inner the seven planets' spheres are the material spheres (''grosso modo'', the Earth); outside, the "sphere of fixed stars."


In [[Roman Empire]], the planets became knowed directly by the name of the associated deity - not the greek one, bet the latin correspondent god. So, ''Phainon'' became ''Saturnus''; ''Phaethon'' was called ''Jupiter'';  ''Pyroeis'' was ''Mars''; ''Phosphoros'', ''Venus'' and ''Stilbon'' was turned to ''Mercurius''. In [[medieval era]], the future european people has herited the roman culture, and so these latinized version of planet's names remain in the vocabulary until present days. Also in latinian tratition (followed by the germanic one) the seven days of the [[week]] have the names of the seven planets.
In the [[Roman Empire]], the planets became known directly by the name of the associated deity - not the Greek one, bet the corresponding Latin god. So, ''Phainon'' became ''Saturnus''; ''Phaethon'', ''Jupiter'';  ''Pyroeis'', ''Mars''; ''Phosphoros'', ''Venus''; and ''Stilbon'', ''Mercurius''. These Latinized names remain current in European languages. Also in the Latin tradition, as well as the Germanic, the seven days of the [[week]] have the names of the seven planets.


After the [[Copernican Revolution]], however, the idea of planet has changed: they are all the bodies that round the Sun - that therefore would be considered just a [[star]] like any other from the firmament. The [[Earth]] then turn into a planet, the [[Moon]] became an Earth's [[sattelite]], and the so-called "Solar System" have then six planets. Later, three new bodies, that can't be seen with [[naked eye]] are baptized as a planet, following the latin-named tradition: ''Uranus'', ''Neptunus'' and ''Pluto''.  
After the [[Copernican Revolution]], however, the definition of a planet changed: they are all the bodies that orbit the Sunthe [[Earth]] thus turns into a planet, the [[Moon]] becomes Earth's [[satellite]] instead of being a planet, and the so-called "Solar System" then has six planets. Later, three new bodies, that can't be seen with the naked eye were baptized as planets, following the Latin-name tradition: ''Uranus'', ''Neptune'' and ''Pluto''.  


But many other small bodies are saying to orbit the Sun, such as the brights [[comets]] and the palid [[asteroid]]s. The crisis in definition starts in 1980's and 1990's, when many bodies so big as - or, in few cases, bigger - Pluto start to be discovered above Neptune's orbit. Called [[Transneptunian objects]], they opened the discussion about what could be a good and precise definition of planet. The discussion ends in August 24, 2006, when [[International Astronomical Union | IAU]] voted the Resolution that defines officially the term. <ref name=IAU>{{ cite web | title = IAU 2006 General Assembly: Result of the IAU Resolution votes | url = http://www.iau2006.org/mirror/www.iau.org/iau0603/index.html | year = 2006 | accessdate = 2007-04-30 }}</ref>
But many other small bodies orbit the Sun, such as the bright [[comet]]s and the pallid [[asteroid]]s. The crisis in definition started in the 1980's and 1990's, when many bodies as big as -- or, in a few cases, bigger than -- Pluto started to be discovered beyond Neptune's orbit. Called [[Transneptunian objects]], they sparked a discussion about what could be a good and precise definition of "planet." The discussion ended on August 24, 2006, when the IAU approved a resolution that officially defines the term. <ref name=IAU>{{ cite web | title = IAU 2006 General Assembly: Result of the IAU Resolution votes | url = http://www.iau2006.org/mirror/www.iau.org/iau0603/index.html | year = 2006 | accessdate = 2007-04-30 }}</ref>


==Physical Formation==
==Physical Formation==


Planets are believed to form form a the disk of dust that surrounds a newly formed star. Gravitation forces pull the dust into lumps. The lumps gradually collide and join to make larger lumps or [[asteroid]]s. These join further to make larger and larger planets until the planet has cleared it's orbit of objects.
Planets are believed to form from the disk of dust that surrounds a newly formed star. Gravitational forces pull the dust into lumps. The lumps gradually collide and join to make larger lumps or asteroids. These join further to make larger and larger planets until the planet has cleared its orbit of objects.


==Planets and Astrology==
==Planets and Astrology==


The orbits of the planets also have a bearing in [[Astrology]]. It is believed the the position of the planets within various [[constellation]]s of stars can be an indicator of events on Earth. By carefully measuring the orbits and positions of the planets and calculating their future paths, it is believed that one can predict future events.
The orbits of the planets also have a bearing on [[Astrology]], believers in which claim that the position of the planets within various [[constellation]]s of stars can be an indicator of events on Earth. By carefully measuring the orbits and positions of the planets and calculating their future paths, it is believed, one can predict future events.


==References==
==References==
<references />
<references />

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According to the International Astronomical Union (IAU), a planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity (but not massive enough to cause thermonuclear fusion in its inner core), and has cleared its neighbouring region of planetesimals. [1] [2] There are eight bodies in the Solar Sysytem that meet this definition: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

Bodies that orbit the sun and are rounded by their own gravity, but have not cleared the neighbourhood, are called "dwarf planets." One of them is Pluto, which was formerly considered a planet. Other bodies orbiting the Sun are generically called "small bodies of the Solar System."

Another related term is "exoplanet." Although there is no official defition for this term, it is often used to indicate bodies analogous to the planets, but that orbit stars other than the Sun.[3]

The Planets

The planets can be subdivided into two main groups. The inner 4 terrestrial planets have a rocky composition. They are relatively small in size. The outer 4 planets are known as Gas Giants and have a thick gaseous atmospheres.

Table of the Planets

Name Distance from the sun Diameter Mass Date of Discovery
Mercury 57,910,000 km (0.38 AU) 4,880 km 3.30e23 kg known in antiquity
Venus 108,200,000 km (0.72 AU) 12,103.6 km 4.869e24 kg known in antiquity
Earth 149,600,000 km (1.00 AU) 12,756.3 km 5.972e24 kg
Mars 227,940,000 km (1.52 AU) 6,794 km 6.4219e23 kg known in antiquity
Jupiter 778,330,000 km (5.20 AU) 142,984 km 1.900e27 kg known in antiquity
Saturn 1,429,400,000 km (9.54 AU) 120,536 km (equatorial) 5.68e26 kg known in antiquity
Uranus 2,870,990,000 km (19.218 AU) 51,118 km (equatorial) 8.683e25 kg 1781
Neptune 4,504,000,000 km (30.06 AU) 49,532 km 1.0247e26 kg 1846

Etymology and History

The word "planet" came from the greek πλανήτ- (planēt-), meaning "wanderers." Before the invention of the telescope, there were seven planets visible in the sky; the ancient Greeks considered each one to be dedicated to a deity:

  • Phainon, "the shiner," dedicated to Cronos;
  • Phaethon, also meaning "shining," brighter than the first, dedicated to Zeus;
  • Pyroeis, "fiery", the red one, dedicated to Ares;
  • Phosphoros, "light bringer", the brightest one, dedicated to Aphrodite;
  • Stilbon, the "gleamer," dedicated to Hermes; [4]

as well as the Sun and Earth's Moon, the biggest wanderers in the sky. Philosophers in antiquity created many models of the universe, of which the best-known is Aristotle's. In his system, each planet belongs to one crystalline sphere, concentric with the others. Inner the seven planets' spheres are the material spheres (grosso modo, the Earth); outside, the "sphere of fixed stars."

In the Roman Empire, the planets became known directly by the name of the associated deity - not the Greek one, bet the corresponding Latin god. So, Phainon became Saturnus; Phaethon, Jupiter; Pyroeis, Mars; Phosphoros, Venus; and Stilbon, Mercurius. These Latinized names remain current in European languages. Also in the Latin tradition, as well as the Germanic, the seven days of the week have the names of the seven planets.

After the Copernican Revolution, however, the definition of a planet changed: they are all the bodies that orbit the Sun; the Earth thus turns into a planet, the Moon becomes Earth's satellite instead of being a planet, and the so-called "Solar System" then has six planets. Later, three new bodies, that can't be seen with the naked eye were baptized as planets, following the Latin-name tradition: Uranus, Neptune and Pluto.

But many other small bodies orbit the Sun, such as the bright comets and the pallid asteroids. The crisis in definition started in the 1980's and 1990's, when many bodies as big as -- or, in a few cases, bigger than -- Pluto started to be discovered beyond Neptune's orbit. Called Transneptunian objects, they sparked a discussion about what could be a good and precise definition of "planet." The discussion ended on August 24, 2006, when the IAU approved a resolution that officially defines the term. [1]

Physical Formation

Planets are believed to form from the disk of dust that surrounds a newly formed star. Gravitational forces pull the dust into lumps. The lumps gradually collide and join to make larger lumps or asteroids. These join further to make larger and larger planets until the planet has cleared its orbit of objects.

Planets and Astrology

The orbits of the planets also have a bearing on Astrology, believers in which claim that the position of the planets within various constellations of stars can be an indicator of events on Earth. By carefully measuring the orbits and positions of the planets and calculating their future paths, it is believed, one can predict future events.

References

  1. 1.0 1.1 IAU 2006 General Assembly: Result of the IAU Resolution votes (2006). Retrieved on 2007-04-30.
  2. Working Group on Extrasolar Planets (WGESP) of the International Astronomical Union. IAU (2001). Retrieved on 2006-05-25.
  3. Error on call to Template:cite web: Parameters url and title must be specified.
  4. James Evans (1998). The History and Practice of Ancient Astronomy. Oxford University Press, 296-7.