Utente:Lo Scaligero/Sandbox: differenze tra le versioni

Versione delle 12:04, 27 set 2008

Versione delle 20:58, 27 set 2008

Riga 50:

=[[:en:Solar System|Solar System]]=

ItLa isluminosità believeddel thatSole the Sun's position on the main sequence puts itè in thecostante "prime of life" for a starcrescita, ine thatsi itè hasstimato notche yetall'inizio exhausteddella itssua storestoria of hydrogenaveva forsoltanto nuclear fusion. The Sun is growing brighter; early in its history it wasil 75% percent as brightdella asluminosità itche ismostra todayattualmente.<ref name="Kasting">{{cite journal |last=Kasting |first=J.F. |coauthors=Ackerman, T.P. |year=1986 |title=Climatic Consequences of Very High Carbon Dioxide Levels in the Earth's Early Atmosphere |journal=Science |volume=234 |pages=1383–1385 |doi=10.1126/science.11539665 |pmid=11539665}}</ref>

[[Image:Sun in X-Ray.png|thumb|right|The Sun as seen in the [[x-ray]] region of the [[electromagnetic spectrum]]]]

Il Sole è una stella ho popolazione, ma è nato in fasi successive della evoluzione del cosmo. Esso contiene più elementi di peso superiore a idrogeno e di elio ( "metalli" nella parlata astronomico) di popolazione anziana stelle II [3]. Elementi di peso superiore a idrogeno e di elio si sono formati nel core di antiche e che esplodono stelle, in modo che la prima generazione di stelle ha prima di morire l'universo potrebbe essere arricchito con questi atomi. La più antica stelle contenere alcuni metalli, mentre stelle nato dopo avere di più. Questo metallicit alto è il pensiero di essere stato cruciale per la domenica di sviluppo di un sistema planetario, perché pianeti forma di accumulo di metalli [4].

The Sun is the Solar System's parent star, and far and away its chief component. Its large mass gives it an interior [[density]] high enough to sustain [[nuclear fusion]], which releases enormous amounts of [[energy]], mostly [[radiant energy|radiated]] into [[outer space|space]] as [[electromagnetic radiation]] such as [[visible spectrum|visible light]].

The Sun is classified as a moderately large [[yellow dwarf]], but this name is misleading as, compared to stars in [[Milky Way|our galaxy]], the Sun is rather large and bright. Stars are classified by the [[Hertzsprung-Russell diagram]], a graph which plots the brightness of stars against their surface [[temperature]]s. Generally, hotter stars are brighter. Stars following this pattern are said to be on the [[main sequence]]; the Sun lies right in the middle of it. However, stars brighter and hotter than the Sun are rare, while stars dimmer and cooler are common.<ref>{{cite web |year=2001 |author=Smart, R. L.; Carollo, D.; Lattanzi, M. G.; McLean, B.; Spagna, A. |title=The Second Guide Star Catalogue and Cool Stars |work=Perkins Observatory |url=http://adsabs.harvard.edu/abs/2001udns.conf..119S |accessdate=2006-12-26}}</ref>

It is believed that the Sun's position on the main sequence puts it in the "prime of life" for a star, in that it has not yet exhausted its store of hydrogen for nuclear fusion. The Sun is growing brighter; early in its history it was 75 percent as bright as it is today.<ref name="Kasting">{{cite journal |last=Kasting |first=J.F. |coauthors=Ackerman, T.P. |year=1986 |title=Climatic Consequences of Very High Carbon Dioxide Levels in the Earth's Early Atmosphere |journal=Science |volume=234 |pages=1383–1385 |doi=10.1126/science.11539665 |pmid=11539665}}</ref>

The Sun is a [[metallicity|population I star]]; it was born in the later stages of the [[Universe#Evolution|universe's evolution]]. It contains more elements heavier than hydrogen and helium ("[[metallicity|metals]]" in astronomical parlance) than older population II stars.<ref>{{cite journal |author=T. S. van Albada, Norman Baker |title=On the Two Oosterhoff Groups of Globular Clusters |journal=Astrophysical Journal |volume=185 |year=1973 |pages=477–498 |doi=10.1086/152434}}</ref> Elements heavier than hydrogen and helium were formed in the [[solar core|cores]] of ancient and exploding stars, so the first generation of stars had to die before the universe could be enriched with these atoms. The oldest stars contain few metals, while stars born later have more. This high metallicity is thought to have been crucial to the Sun's developing a [[planetary system]], because planets form from accretion of metals.<ref> {{cite web |title=An Estimate of the Age Distribution of Terrestrial Planets in the Universe: Quantifying Metallicity as a Selection Effect |author=Charles H. Lineweaver |work=University of New South Wales |date=2001-03-09 |url=http://arxiv.org/abs/astro-ph/0012399 |accessdate=2006-07-23}}</ref>