Related topics: stars
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
Starring Intelligent Aliens
Nov 05, 2009 |
4.6 / 5 (8) |
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The most probable place to find intelligent life in the galaxy is around stars very similar to our sun, a new study has found.
Unsettled Youth: Spitzer Observes a Chaotic Planetary System
Nov 04, 2009 |
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(PhysOrg.com) -- Before our planets found their way to the stable orbits they circle in today, they wiggled and jostled about like unsettled children. Now, NASA's Spitzer Space Telescope has found a young ...
Icebreaker: Scientist brings out big gun to explore behavior of ice in planetary collisions
Space & Earth / Space Exploration
Oct 29, 2009 |
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(PhysOrg.com) -- Every month, Sarah Stewart-Mukhopadhyay fires her 20-foot gun in the basement of Harvard's Hoffman Lab, sending shivers through the concrete and steel structure that can be picked up by seismometers ...
Detecting Life-Friendly Moons
Space & Earth / Space Exploration
Oct 26, 2009 |
4.8 / 5 (11) |
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The search for life-friendly real estate around distant stars doesn't have to be limited to planets. New research shows that habitable exomoons can be detected with a new method using current technology.
Building Planet Earth
Oct 22, 2009 |
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A new study shows how rocky planets are formed from the manic swirl of gas and dust that surround a young star, and determines what chemical building blocks are used to construct the planets. Understanding ...
Astronomers do it Again: Find Organic Molecules Around Gas Planet (w/ Video)
Oct 20, 2009 |
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(PhysOrg.com) -- Peering far beyond our solar system, NASA researchers have detected the basic chemistry for life in a second hot gas planet, advancing astronomers toward the goal of being able to characterize ...
32 New Exoplanets Found (w/ Video)
Oct 19, 2009 |
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(PhysOrg.com) -- Today, at an international ESO/CAUP exoplanet conference in Porto, the team who built the High Accuracy Radial Velocity Planet Searcher, better known as HARPS, the spectrograph for ESO's 3.6-metre ...
Dirty stars make good solar system hosts (w/ Video)
Oct 06, 2009 |
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Some stars are lonely behemoths, with no surrounding planets or asteroids, while others sport a skirt of attendant planetary bodies. New research published this week in The Astrophysical Journal Letters explains why the co ...
The Hot Saturn Exoplanet
Oct 02, 2009 |
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(PhysOrg.com) -- Of the roughly 350 known exoplanets (i.e., extrasolar planets), the one orbiting the star HD149026 is unique.
Cloudy with a chance of pebble showers: Simulation suggests rocky exoplanet has bizarre atmosphere
Sep 29, 2009 |
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(PhysOrg.com) -- So accustomed are we to the sunshine, rain, fog and snow of our home planet that we find it next to impossible to imagine a different atmosphere and other forms of precipitation.
Planet Imager will enable telescopes to image extrasolar planets directly
Sep 29, 2009 |
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The best way to observe objects in solar systems is simply to look -- but distortions caused by Earth's atmosphere drown out much of the spectacle of space. To address this problem, Berkeley astronomer James ...
The discovery of new Earths is imminent, UD astronomer says
Sep 28, 2009 |
4 / 5 (16) |
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(PhysOrg.com) -- Harry Shipman, Annie Jump Cannon Professor of Physics and Astronomy at the University of Delaware, told the audience for his lecture, “Seeking New Planets,” on Saturday evening, Sept. 26, ...
Sea level stargazing: Astronomers make key sighting with Florida telescope
Sep 28, 2009 |
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(PhysOrg.com) -- This summer, University of Florida astronomers inaugurated the world's largest optical telescope on a nearly 8,000-foot mountaintop 3,480 miles away. But it was a far more modest observatory, located just ...
Ganymede makes big impression on Jupiter's auroral lightshows (w/ Video)
Sep 18, 2009 |
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(PhysOrg.com) -- Studies of features in Jupiter’s spectacular and rapidly changing aurorae have given new insights into the complex electromagnetic interactions between the giant planet and two of its innermost ...
Asteroid Juno Grabs the Spotlight
Space & Earth / Space Exploration
Sep 17, 2009 |
3 / 5 (1) |
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(PhysOrg.com) -- Toward the end of September, the sun will turn a spotlight on the asteroid Juno, giving that bulky lump of rock a rare featured cameo in the night sky. Those who get out to a dark, unpolluted ...
