Related topics: stars , solar system , exoplanet , nasa , earth
Planet
hideA planet (from Greek πλανήτης, from the verb πλανώμαι planōmai I wander), is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.[a]
The term planet is ancient, with ties to history, science, myth, and religion. The planets were originally seen by many early cultures as divine, or as emissaries of the gods. Even today, many people believe in astrology, which holds that the movement of the planets affects people's lives, although such a causation is rejected by the scientific community. As scientific knowledge advanced, human perception of the planets changed, incorporating a number of disparate objects. Even now there is no uncontested definition of what a planet is. In 2006, the IAU officially adopted a resolution defining planets within the Solar System. This definition has been both praised and criticized, and remains disputed by some scientists.
The planets were thought by Ptolemy to orbit the Earth in deferent and epicycle motions. Though the idea that the planets orbited the Sun had been suggested many times, it was not until the 17th century that this view was supported by evidence from the first telescopic astronomical observations, performed by Galileo Galilei. By careful analysis of the observation data, Johannes Kepler found the planets' orbits to be not circular, but elliptical. As observational tools improved, astronomers saw that, like Earth, the planets rotated around tilted axes, and some share such features as ice-caps and seasons. Since the dawn of the Space Age, close observation by probes has found that Earth and the other planets share characteristics such as volcanism, hurricanes, tectonics, and even hydrology. Since 1992, through the discovery of hundreds of extrasolar planets (planets around other stars), scientists are beginning to understand that planets throughout the Milky Way Galaxy share characteristics in common with our own.
Planets are generally divided into two main types: large, low-density gas giants, and smaller, rocky terrestrials. Under IAU definitions, there are eight planets in the Solar System. In order from the Sun, they are the four terrestrials, Mercury, Venus, Earth, and Mars, then the four gas giants, Jupiter, Saturn, Uranus, and Neptune. The Solar System also contains at least five dwarf planets: Ceres, Pluto (originally classified as the Solar System's ninth planet), Makemake, Haumea and Eris. With the exception of Mercury, Venus, Ceres and Makemake, all of these are orbited by one or more natural satellites.
As of June 2009, there are 353 known extrasolar planets, ranging from the size of gas giants to that of terrestrial planets.
For more information about Planet, read the full article at
Wikipedia.
This text uses material from Wikipedia and is available under the GNU Free Documentation License.
News tagged with planets
A New Method of Estimating Stellar Distances
9 hours ago |
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(PhysOrg.com) -- The star Chi Cygni is located about 550 light-years away, in the direction of the constellation of Cygnus the Swan. It is a notable star because, unlike the sun which still burns hydrogen ...
Avatar's moon Pandora could be real
Dec 17, 2009 |
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In the new blockbuster Avatar, humans visit the habitable - and inhabited - alien moon called Pandora. Life-bearing moons like Pandora or the Star Wars forest moon of Endor are a staple of science fiction. ...
Astronomers Find Super-Earth Using Amateur, Off-the-Shelf Technology (w/ Video)
Dec 16, 2009 |
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(PhysOrg.com) -- Astronomers announced today that they have discovered a "super-Earth" orbiting a red dwarf star 40 light-years from Earth. They found the distant planet with a small fleet of ground-based ...
Giant Planet Set for a Cataclysmic Show
Dec 16, 2009 |
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(PhysOrg.com) -- A team of Chinese astronomers have discovered a giant planet close to the exotic binary star system QS Virginis. Although dormant now, in the future the two stars will one day erupt in a violent ...
First Direct Imaging of a Young Binary System
Dec 15, 2009 |
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(PhysOrg.com) -- A team of astronomers from The Graduate University for Advanced Studies, the National Astronomical Observatory of Japan, and other universities have captured the first direct image of a young ...
New planet discoveries suggest low-mass planets are common around nearby stars (w/ Video)
Dec 14, 2009 |
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(PhysOrg.com) -- An international team of planet hunters has discovered as many as six low-mass planets around two nearby Sun-like stars, including two "super-Earths" with masses 5 and 7.5 times the mass of ...
WISE satellite blasts off on space-map mission
Space & Earth / Space Exploration
Dec 14, 2009 |
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NASA launched Monday a new breed of satellite called WISE on a mission to orbit Earth and map the skies to find elusive cosmic objects, including potentially dangerous asteroids.
Rare Scottish mineral may indicate life on Mars
Space & Earth / Space Exploration
Dec 10, 2009 |
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(PhysOrg.com) -- A team of NASA (National Aeronautics and Space Administration) scientists is looking for clues about life on Mars in an earthy clay mineral found only in Aberdeenshire in Scotland.
Superior Super Earths
Space & Earth / Space Exploration
Nov 30, 2009 |
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Super Earths are named for their size, but these planets - which range from about 2 to 10 Earth masses - could be superior to the Earth when it comes to sustaining life. They could also provide an answer to ...
3 Questions: Sara Seager on searching for Earth-like planets
Nov 23, 2009 |
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(PhysOrg.com) -- MIT planetary scientist Sara Seager has been studying exoplanets — planets circling stars other than the sun — for many years.
Spitzer Telescope Observes Baby Brown Dwarf
Nov 23, 2009 |
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(PhysOrg.com) -- NASA's Spitzer Space Telescope has contributed to the discovery of the youngest brown dwarf ever observed -- a finding that, if confirmed, may solve an astronomical mystery about how these ...
Planet 51 Star Brings NASA's Message of Exploration Down to Earth
Space & Earth / Space Exploration
Nov 20, 2009 |
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(PhysOrg.com) -- Actor Dwayne Johnson, usually known for his action and comedic film roles, takes to the stars as an astronaut in a new animated feature that brings important messages about the importance of space exploration ...
Hunting for Planets in the Dark
Nov 19, 2009 |
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A proposed space mission that aims to measure dark energy could also detect planets that current surveys are unable to find.
Discovery of a Retrograde or Highly Tilted Extrasolar Planet
Nov 18, 2009 |
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Astronomers have found that the extrasolar planet HAT-P-7b has a retrograde or highly tilted orbit. Studying such planets is important in understanding the diversity of planetary systems and assessing current ...
Dawn Enters Asteroid Belt -- For Good
Space & Earth / Space Exploration
Nov 16, 2009 |
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(PhysOrg.com) -- NASA's Dawn spacecraft re-entered our solar system's asteroid belt today, Nov. 13, and this time it will stay there.
