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 plane
Pioneering Swiss solar-powered plane rolled out
Nov 06, 2009 |
4.3 / 5 (8) |
0
Solar Impulse, the Swiss bid to make the first solar-powered flight around the world, rolled out its prototype on Friday at an airbase near Zurich and powered up the engines.
Flying and pregnant? Follow doctor's orders
Oct 20, 2009 |
not rated yet |
0
The Boston woman was in her 38th week of pregnancy when a close family member died in New York City. She asked her obstetrician, Dr. William Barth Jr. of Massachusetts General Hospital, if traveling to the funeral was out ...
NASA flies over Antarctica to measure icemelt
Space & Earth / Earth Sciences
Oct 16, 2009 |
3.4 / 5 (9) |
1
(AP) -- Hoping to better understand how a melting Antarctica could swamp the planet, a NASA plane outfitted with lasers and ground-penetrating radar made its first flight over the icy continent on Friday.
Satellite data look behind the scenes of deadly earthquake
Space & Earth / Earth Sciences
Oct 15, 2009 |
4.6 / 5 (7) |
0
Using satellite radar data and GPS measurements, Chinese researchers have explained the exceptional geological events leading to the 2008 Wenchuan Earthquake that killed nearly 90 000 people in China's Sichuan ...
Capturing images in non-traditional way may benefit AF
Jul 14, 2009 |
4.3 / 5 (3) |
0
New research in imaging may lead to advancements for the Air Force in data encryption and wide-area photography with high resolution.
Space companies eye HI as potential new frontier
Space & Earth / Space Exploration
Jul 12, 2009 |
2.8 / 5 (4) |
3
(AP) -- Tourists coming to Hawaii for high-end getaways could someday be launched from the sand to the stars, taking island-hopping to new heights. Hawaii could even be the first state where space travelers ...
Jatropha Helps Air New Zealand Cut Its CO2 Emissions by More Than 60%
Jun 17, 2009 |
3.8 / 5 (14) |
14
Recently, Air New Zealand ran a test flight of a jet plane fueled with a biofuel blend made with jatropha. The results showed a fuel savings of 1.2%, amounting to more than a ton of fuel over the course of ...
Experts mull over lessons from Brazil plane crash
Jun 05, 2009 |
not rated yet |
0
(AP) -- The mysterious disappearance of an Air France jet this week while flying over the Atlantic in fierce thunderstorms is stirring a debate about whether new technologies and procedures are needed to prevent similar ...
Lightning bolts a risk for modern jets
Jun 02, 2009 |
not rated yet |
8
Passenger jets are hit by lightning every 1,000 hours -- on average twice a year -- and experts say the risk from the bolts of electricity is growing.
Signal failure indicates 'rapid' Air France catastrophe: official
Jun 01, 2009 |
5 / 5 (1) |
0
No signal has been heard from distress beacons on a missing Air France plane, indicating it suffered a "very rapid" catastrophe, a top French space agency official told AFP on Monday.
Resolving a galactic mystery
Apr 29, 2009 |
4.8 / 5 (19) |
3
An extremely deep Chandra X-ray Observatory image of a region near the center of our Galaxy has resolved a long-standing mystery about an X-ray glow along the plane of the Galaxy. The glow in the region covered ...
Four of Saturn's moons parade by their parent
Space & Earth / Space Exploration
Mar 17, 2009 |
4.7 / 5 (3) |
0
On 24 February 2009, the NASA/ESA Hubble Space Telescope captured a photo sequence of four moons of Saturn passing in front of their parent planet. The moons, from far left to right, are the white icy moons ...
Road-worthy plane? Or sky-worthy car?
Feb 03, 2009 |
4.4 / 5 (7) |
11
(PhysOrg.com) -- What began as an MIT student project has evolved into a working prototype of a two-seater airplane that can be quickly converted into a road-worthy car. The car-plane has begun test flights ...
Can you see me now? Flexible photodetectors could help sharpen photos
Jan 13, 2009 |
4.8 / 5 (11) |
0
(PhysOrg.com) -- Distorted cell-phone photos and big, clunky telephoto lenses could be things of the past. UW-Madison Electrical and Computer Engineering Associate Professor Zhenqiang (Jack) Ma and colleagues ...
James Webb Telescope components pass tests
Space & Earth / Space Exploration
Sep 17, 2008 |
5 / 5 (1) |
0
You might think that shaking and freezing a state-of-the-art, meticulously crafted machine is a bad idea. But when it comes to firing telescopes and their instruments into the frigid cold of space, the more ...
- Pages: 1
