Dictionary
(astronomy) a celestial body of hot gases that radiates energy derived from thermonuclear reactions in the interior someone who is dazzlingly skilled in any field any celestial body visible (as a point of light) from the Earth at night an actor who plays a principal role a plane figure with 5 or more points often used as an emblem a performer who receives prominent billing a star-shaped character * used in printing the topology of a network whose components are connected to a hub feature as the star "The movie stars Dustin Hoffman as an autistic man" be the star in a performance mark with an asterisk "Linguists star unacceptable sentences" indicating the most important performer or role "the leading man" "prima ballerina" "prima donna" "a star figure skater" "the starring role" "a stellar role" "a stellar performance"
|
Wikipedia
This article is about celestial bodies.'' otheruses star cluster]]A star is a massive body of plasma in outer space that is currently producing or has produced energy through nuclear fusion. Unlike a planet, from which most light is reflected, a star emits light because of its intense blackbody radiation heat. Scientifically, stars are defined as !Gravity#Self-gravitating_syste mself-gravitating spheres of plasma in hydrostatic equilibrium, which generate their own energy through the process of nuclear fusion. Small (''dwarf'') stars such as the Sun generally have essentially featureless disks with only small sunspotsstarspots. Larger (''giant'') stars have much bigger, much more obvious starspots, and also exhibit strong stellar limb-darkening (the brightness decreases towards the edge of the stellar disk). Stellar astronomy is the study of stars.All stars except the Sun appear to the human eye as shining points in the nighttime sky that Scintillation (astrophysics)twinkle because of the effect of the Earth's atmosphere. Interferometer telescopes are required in order to produce images of these objects. The Sun is also a star, but it is close enough to Earth to appear as a disk instead, and to provide sunlightdaylight. Stars are not spread uniformly across the universe, but are typically grouped into galaxygalaxies. A typical galaxy contains hundreds of billions of stars. The majority of stars are gravitationally bound to other stars, forming binary stars. Larger groups called star clusters also exist. Astronomers estimate that there are at least 70 sextillion !(7×1022news.bbc.co.uk. That is 70 000 000 000 000 000 000 000, or 230 billion times as many as the 300 billion in our own Milky Way.Many stars are between 1 billion and 10 billion years old. Some stars may even be close to 13.7 billion years old, which is the observed age of the universe. (See Big BangBig Bang theory and stellar evolution.) They range in size from the tiny neutron stars (which are actually dead stars) no bigger than a city, to supergiants like the North Star (Polaris) and Betelgeuse, in the Orion (constellation)Orion constellation, which have a diameter about 1,000 times larger than the Sun —about 1.6 terametres. However, these have a much lower density than the Sun.One of the most massive stars known is Eta Carinaeη Carinae, with 100–150 times as much mass as the Sun. Recent work by Donald Figer, an astronomer at the Space Telescope Science Institute in Baltimore, Maryland, suggests that 150 solar masses is the upper limit of stars in the current era of the universe. He used the Hubble Space Telescope to observe about a thousand stars in the Arches cluster, a massive young star cluster near the Galactic Centercore of the Milky Way, and found no stars over that limit despite a statistical expectation that there should be several. The reason for this limit is not precisely known, but the Eddington limit is part of the answer. The very first stars to form after the Big Bang may have been larger, up to 300 solar masses or more, due to the complete absence of elements heavier than lithium in their composition. This generation of supermassive star is long extinct, however, and currently only theoretical.With a mass only 93 times that of Jupiter (planet)Jupiter, AB Doradus C, a companion to AB Doradus A, is the smallest known star undergoing nuclear fusion in its core. Smaller bodies are brown dwarfs, which occupy a poorly-defined grey area between stars and gas giants. The minimum mass a star can have is estimated to be in the vicinity of 75 Jupiters.The energy produced by stars radiationradiates into space as electromagnetic radiation, as a stream of neutrinos from the star's core, and as a stream of particles from the star's outer layers (its stellar wind). The peak frequency of the light depends on the temperature of the outer layers of the star. Besides the emitted visible light, the ultraviolet and infrared components are typically significant. The apparent brightness of a star is measurementmeasured by its apparent magnitude.The nearest star to the Earth, apart from the Sun, is Proxima Centauri, which is 39.9 trillion kilometres, or 4.2 light years away (light from Proxima Centauri takes 4.2 years to reach Earth). Travelling at the orbit speed of the Space Shuttle (5 miles per second -- almost 30,000 kilometers per hour), it would take about 150,000 years to get there. Distances like this are typical inside galactic discs, where the Sun and Earth are located. Stars can be much closer to each other in the centres of galaxies and globular clusters, or much further apart in galactic halos.
Star formation and evolution - As learned by star formation astronomers, stars are born in molecular clouds, large regions of slightly higher density of matter (though still less dense than the inside of an earthly vacuum chamber), and form by gravitational instability inside those clouds triggered by shockwaves from supernovae. High mass stars powerfully illuminate the clouds from which they formed. One example of such a nebula is the Orion Nebula.Stars spend about 90% of their lifetime nuclear fusionfusing hydrogen to produce helium in high-pressure reactions near the core. Such stars are said to be on the main sequence.Small stars (called red dwarfs) burn their fuel very slowly and last tens to hundreds of billions of years (far longer than the time elapsed in the universe so far). At the end of their lives, they simply become dimmer and dimmer, fading into black dwarfs —although none exist yet.As most stars exhaust their supply of hydrogen, their outer layers expand and cool to form a red giant. In about 5 billion years, when the Sun is a red giant, it will subsume Mercury (planet)Mercury and Venus (planet)Venus. Eventually the core is compressed enough to start helium fusion, and the star heats up and contracts. Larger stars will also fuse heavier elements, all the way to iron, which is the end point of the process.An average-size star will then shed its outer layers as a planetary nebula. The core that remains will be a tiny ball of degenerate matter not massive enough for further fusion to take place, supported only by degeneracydegeneracy pressure, called a white dwarf. It will fade into a black dwarf over very long stretches of time.In larger stars, fusion continues until gravitational collapsecollapse ends up causing the star to explode in a supernova. This is the only cosmic process that happens on human timescales; historically, supernovae have been observed as "new stars" where none existed before. Most of the matter in a star is blown away in the explosion (forming nebulae such as the Crab Nebula) but what remains will collapse into a neutron star (a pulsar or X-ray burster) or, in the case of the largest stars, a black hole.The blown-off outer layers include heavy Chemical elementelements, which are often converted into new stars and/or planets. The outflow from supernovae and the solar windstellar wind of large stars play an important part in shaping the interstellar medium.Stellar evolution explains how stars are created and die in greater detail.
Star classification - There are different stellar classificationclassifications of stars ranging from type W which are very large and bright, to M which is often just large enough to start ignition of the hydrogen. Some of the more common classifications are O, B, A, F, G, K, M, and can perhaps be more easily remembered using the mnemonic "Oh, Be A Fine Girl, Kiss Me" (variant: change "girl" to "guy"), invented by Annie Jump Cannon (1863-1941). There are many List of mnemonics for star classificationother mnemonics for star classification; the most frequent addition tacks Right Now Sweetheart for the red dwarf sub-types R, N and S. Each letter has 9 subclassifications. Our Sun is a G2, which is very near the middle in terms of quantities observed. Most stars fall into the main sequence which is a description of stars based on their absolute magnitude and spectral type. The Sun is taken as the prototypical star (not because it is special in any way, but because it is the closest and most studied star we have), and most characteristics of other stars are usually given in solar units.
For example, the mass of the Sun !isM''Sun30? kilogramkgThe masses of other stars can be given in terms of Solar mass!MSun.
Naming of stars - Most stars are identified only by catalogue numbers; only a few have names as such. The names are either traditional names (mostly from Arabic), Flamsteed designations, or Bayer designations. The only body which has been recognized by the scientific community as having competence to name stars or other celestial bodies is the International Astronomical Union (IAU). A number of private companies (e.g. the "International Star Registry") purport to sell names to stars; however, these names are not recognized by the scientific community, nor used by them, and many in the astronomy community view these organizations as frauds preying on people ignorant of how stars are in fact named. See star designations for more information on how stars are named. For a list of traditional names, see the list of stars by constellation.
Nuclear fusion reaction pathways - A variety of different nuclear fusion reactions take place inside the cores of stars, depending upon their mass and composition (see Stellar nucleosynthesis).Stars begin as a cloud of mostly hydrogen with about 25% helium and heavier elements in smaller quantities. In the Sun, with a 107 K core, hydrogen fuses to form helium in the proton-proton chain::4protium1H → 2deuterium2H + 2positrone+ + 2neutrinoνe (4.0 Melectron volteV + 1.0 !MeV):21 H? + 22H → 2Helium-33He + 2gamma rayγ (5.5 !MeV):23 He? → Helium-44He + 21H (12.9 MeV)These reactions result in the overall !reaction::41H? → 4He + 2e+ + 2γ + 2νe (26.7 MeV)In more massive stars, helium is produced in a cycle of reactions catalystcatalyzed by carbon, the CNO cyclecarbon-nitrogen-oxygen cycle.In stars with cores at 108 K and masses between 0.5 and 10 solar masses, helium can be transformed into carbon in the triple-alpha !process::44He + 92 keV → !8*Be:&l t;sup>4He? + 8*Be + 67 keV → !12*C:&l t;sup>12*C? → Carbon-1212C + γ + 7.4 MeVFor an overall reaction !of::34H e? → 12C + γ + 7.2 MeV
Star mythology - As well as certain constellations and the Sun itself, stars as a whole have their own mythology. They were thought to be the souls of the dead, or gods/goddesses.
References - Cliff Pickover (2001) "The Stars of Heaven", Oxford University Press John Gribbin, Mary Gribbin (2001) "Stardust: Supernovae and Life — The Cosmic Connection", Yale University Press.
See also - Black hole Blue straggler ConstellationOverview of star constellations Nursery rhyme ''Twinkle twinkle little star'' sidereal clock Star count Star clocks Star listingStars with articles in Wikipedia Stellar navigation Stellar evolution Timeline of stellar astronomy Variable star
Related lists - List of brightest starsList of brightest stars (apparent & absolute magnitude) List of heaviest starsList of heaviest stars (by solar mass) List of largest starsList of largest stars (by diameter) List of mnemonics for star classification List of nearest bright stars List of nearest stars List of starsList of the most important stars List of stars by constellation List of stars with confirmed extrasolar planets
External links - mrao.cam.ac.uk - Images of starspots on the surface of Betelgeuse simbad.u-strasbg.fr - Find out what is known about any given star by entering its name or positionCategory:Stars Category:Astronomical !objectsbg:Звездаbs:Zvije zdeca:Estelcs:Hvězdacy:Serend a:Stjernede:SternLink? FAde et:Täht !(astronoomia)es:Estrellaeo:Ste lofa:ستارهfr:Étoileko: 성hr:Zvijezdaio:Steloid:Bint angia:Stellait:Stellahe:כוכ בkn:ನಕ್ಷತ್ರla:S tellalb:Stärhu:Csillag? !(égitest)ms:Bintangnah:Sitial innl:Sterja:恒星no:Stjernepl :Gwiazdapt:Estrelaro:SteaLink? FAro !ru:Звездаscn:Stiddasimpl e:Starsk:Hviezdasl:Zvezdasr:З вездаfi:Tähtisv:Stjärna th:ดาวฤกษ์zh:恒 星
|
|
Websites
Evolution - The Genesis Project
A massive multiplayer online game! Build up your own civilisation and defend it against thousand of other players in the world
http://www.evo-online.com/
Hiclone, Fuelstar, Fuelmax, KNFilters and Oil Filter Magnets are all Fuel Savers
Hiclone, Fuelstar, Fuelmax, KNFilters and Oil Filter Magnets are all Fuel Savers
http://hiclone-fuelmax-hyclone-au.com
xtreme precision
Xtreme is the manufacturer of BB pellets that is setting the industry standards. Manufacturer of the most advanced and accurate BB's for air soft guns. Perfect shape, tight tolerance, high polish and brightness are just some of the features of our products. Xtreme also produce bio degradable BB's and special batteries for air soft guns.
http://www.xtreme-shot.com
>> ASTROLOGYWIZARD.com ::: - paul wade - ::: - astrologer - :::
Astrologer Paul Wade offers free astrology resources, horoscopes, sign analyses, zodiac screensavers, cool games and a directory of recommended links!
http://www.astrologywizard.com/
Ramco Computer & Supplies
We sell copier, fax, printer, typewriter, calculator supplies & mp3 players, dvd, satillite radio and a lot more
http://www.ramcoweb.com/
POS-Savings.com
Your source for receipt printers, cash drawers, barcode scanners, scanner-scales and other POS equipment.
http://www.pos-savings.com/
The Party Fowl
Women's motorcycle, beach & fashion tops & halters decorated in custom Swarovski crystals and gold & silver metallic nailheads. Men's biker T's and denim shirts.
http://www.ThePartyFowl.com/
Robbie Williams Turkey
News, gallery, wallpapers, lyrics, discography and Everything you need to know about Robbie Williams!
http://www.robbiewilliams-tr.com/
Artist Station
The loyale partner for artists and bands
http://www.artiststation.de/
InsiderEntertainment.com
InsiderEntertainment.com ~ the premier creative online manual for metropolitan individuals seeking entertainment and enjoyment in their professional, social and cultural endeavours.
http://www.insiderentertainment.com/
PrinterSavings.com
Your source for barcode, POS (receipt) and ID card printing needs. This includes barcode Printers from Zebra, Cognitive, Datamax and Sato, POS printers from Axiohm, Epson and Ithaca, and ID Card Printers from Fargo, Datacard, Eltron (Zebra Card) and Evolis.
http://www.printersavings.com/
Airsoft
VI.SE.LE. italiana S.r.l. is one of the leading companies in the airsoft industry. Based in Italy the company is specialized in the production and wolesale of air soft guns and accessories for guns. VI.SE.LE. Italiana S.r.l. is owner of the production rights for air soft guns of real gun brands and exclusive distributor for several European countries of the famous air soft brand Classic Army.
http://www.visele.it
Kistner-Art / virtuelle Galerie des Rheinfeldener Kuenstlers Roland Kistner.
Virtuelle Galerie des Rheinfeldener Kuenstlers Roland Kistner, der seine Arbeiten aus Keramik (biomechanische Skulpturen mit zum Teil keltischen Einfluessen), online praesentiert.(Virtual Gallery of the Rheinfelden artist Roland Kistner, who presents his artworks (bio-mechanical sculptures with the occasional Celtic influence) made out of Ceramic, online.)
http://www.kistner-art.de/
Airsoft
VI.SE.LE. italiana S.r.l. is one of the leading companies in the airsoft industry. Based in Italy the company is specialized in the production and wolesale of air soft guns and accessories for guns. VI.SE.LE. Italiana S.r.l. is owner of the production rights for air soft guns of real gun brands and exclusive distributor for several European countries of the famous air soft brand Classic Army.
http://www.classicarmyitalia.com/
akınlastikltd
lastik jant akü yağ yetkili servis ve hizmeti
http://www.akinlastik.com/
Hiclone, Fuelstar, Fuelmax, KNFilters and Oil Filter Magnets are all Fuel Savers
Hiclone, Fuelstar, Fuelmax, KNFilters and Oil Filter Magnets are all Fuel Savers
http://www.hiclones.com
Kärntner Yacht Club Ossiacher See (KYCO) - Segeln Kärnten Segelclub Ossiachersee Regatta-Segeln Österreich
Der Kärntner Yacht Club Ossiacher See (KYCO) ist der Segelclub am Ossiachersee (Österreich). Der Yachtclub informiert über das Regatta-Segeln am Ossiachersee in Kärnten, bietet eine Bootsbörse, Links zum Thema Segeln u.v.m.
http://www.kyco.at/
BSA Troop 270 - Thurmont, MD
Boy Scouts of America Troop 270 of Thurmont Maryland 21788
http://www.troop270.com/
Virtual Twilight - German Homepage about Roleplaying Games, U2, Star Wars and London
A german Website about several Roleplaying Games, such as Shadowrun, Star Wars, Call of Cthulhu and D20. Beside these Main Themes there are also information about the City of London, the irish Rockband U2 an other things.
http://www.virtualtwilight.de/
Hiclone, Fuelstar, Fuelmax, KNFilters and Oil Filter Magnets are all Fuel Savers
Hiclone, Fuelstar, Fuelmax, KNFilters and Oil Filter Magnets are all Fuel Savers
http://www.oilfiltermagnet.com
First Quarter Optics
We specialize in the sales of mainly William Optics Telescopes and accessories. From time to time we also have used equipment and meteorites for sale.
http://www.firstquarteroptics.com/
Hiclone, Fuelstar, Fuelmax, KNFilters and Oil Filter Magnets are all Fuel Savers
Hiclone, Fuelstar, Fuelmax, KNFilters and Oil Filter Magnets are all Fuel Savers
http://www.fuelstar-au.com
StarTrek.com
Official Site. Includes news, interviews, cast biographies, episode guides, and other information.
http://www.startrek.com/
The Toronto Star
Founded in 1892, The Toronto Star is Canada's largest daily newspaper, reaching more than 1.9 million readers daily, Monday to Friday.
http://thestar.com
Star Tribune
Online version of Minneapolis daily newspaper. Site features updated news stories, diversions, weather, archives.
http://www.startribune.com/
The Star Online
Online version of The Star newspaper.
http://thestar.com.my/
Kansascity.com
A city guide sponsored by local media outlets and community organizations. Includes news, entertainment, chat, and local web links.
http://kansascity.com/
The Star
Online English language Jordanian political, economic and cultural weekly.
http://star.arabia.com
|
|