Portal:Stars
Wikipedia portal for content related to Stars / From Wikipedia, the free encyclopedia
Portal maintenance status: (June 2018)
|
IntroductionA star is a luminous spheroid of plasma held together by self-gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night; their immense distances from Earth make them appear as fixed points of light. The most prominent stars have been categorised into constellations and asterisms, and many of the brightest stars have proper names. Astronomers have assembled star catalogues that identify the known stars and provide standardized stellar designations. The observable universe contains an estimated 1022 to 1024 stars. Only about 4,000 of these stars are visible to the naked eye—all within the Milky Way galaxy. A star's life begins with the gravitational collapse of a gaseous nebula of material largely comprising hydrogen, helium, and trace heavier elements. Its total mass mainly determines its evolution and eventual fate. A star shines for most of its active life due to the thermonuclear fusion of hydrogen into helium in its core. This process releases energy that traverses the star's interior and radiates into outer space. At the end of a star's lifetime as a fusor, its core becomes a stellar remnant: a white dwarf, a neutron star, or—if it is sufficiently massive—a black hole. Stellar nucleosynthesis in stars or their remnants creates almost all naturally occurring chemical elements heavier than lithium. Stellar mass loss or supernova explosions return chemically enriched material to the interstellar medium. These elements are then recycled into new stars. Astronomers can determine stellar properties—including mass, age, metallicity (chemical composition), variability, distance, and motion through space—by carrying out observations of a star's apparent brightness, spectrum, and changes in its position in the sky over time. Stars can form orbital systems with other astronomical objects, as in planetary systems and star systems with two or more stars. When two such stars orbit closely, their gravitational interaction can significantly impact their evolution. Stars can form part of a much larger gravitationally bound structure, such as a star cluster or a galaxy. (Full article...) Selected star - show anotherPhoto credit: ESO/P. Kervella
Betelgeuse is a semiregular variable star located approximately 640 light-years from the Earth. With an apparent magnitude ranging between 0.3 and 1.2, it is the ninth brightest star in the night sky. Although Betelgeuse has the Bayer designation Alpha Orionis (α Orionis / α Ori), it is most often the second brightest star in the constellation Orion behind α; Rigel (Beta Orionis) is usually brighter (Betelgeuse is a variable star and is on occasion brighter than Rigel). The star marks the upper right vertex of the Winter Triangle and center of the Winter Hexagon. Betelgeuse is a red supergiant, and one of the largest and most luminous stars known. For comparison, if the star were at the center of the Solar System its surface might extend out to between the orbits of Mars and Jupiter, wholly engulfing Mercury, Venus, the Earth and Mars. The angular diameter of Betelgeuse was first measured in 1920–1921 by Albert Abraham Michelson and Francis G. Pease using the 100 inch (2.5 m) John D. Hooker astronomical interferometer telescope atop Mount Wilson Observatory. Astronomers believe Betelgeuse is only a few million years old, but has evolved rapidly because of its high mass. Due to its age, Betelgeuse may go supernova within the next millennium (because it is hundreds of light years away, it possibly may have done so already). Selected article - show anotherPhoto credit: User:Oliverbeatson
All stars are born from collapsing clouds of gas and dust, often called nebulae or molecular clouds. Nuclear fusion powers a star for most of its life. Stars similar to our Sun gradually grow in size until they reach a red giant phase, after which the core collapses into a dense white dwarf and the outer layers are expelled as a planetary nebula. Larger stars can explode in a supernova as their cores collapse into an extremely dense neutron star or black hole. It is not clear how red dwarfs die because of their extremely long life spans, but they probably experience a gradual death in which their outer layers are expelled over time. Stellar evolution is not studied by observing the life of a single star, as most stellar changes occur too slowly to be detected, even over many centuries. Instead, astrophysicists come to understand how stars evolve by observing numerous stars at various points in their lifetime, and by simulating stellar structure using computer models. A stellar evolutionary model is a mathematical model that can be used to compute the evolutionary phases of a star from its formation until it becomes a remnant. The mass and chemical composition of the star are used as the inputs, and the luminosity and surface temperature are the only constraints. The model formulae are based upon the physical understanding of the star, usually under the assumption of hydrostatic equilibrium. Selected image - show anotherPhoto credit: IAU and Sky & Telescope magazine
Indus is a constellation in the southern sky. Created in the late sixteenth century, it represents an Indian, a word that could refer at the time to any native of Asia or the Americas. Did you know?
SubcategoriesTo display all subcategories click on the ►
Selected biography - show anotherPhoto credit: Portrait from Toruń
Nicolaus Copernicus (19 February 1473 – 24 May 1543) was the first astronomer to formulate a comprehensive heliocentric cosmology, which displaced the Earth from the center of the universe. Nicolaus Copernicus was born on 19 February 1473 in the city of Toruń (Thorn) in Royal Prussia, part of the Kingdom of Poland. Copernicus' epochal book, De revolutionibus orbium coelestium (On the Revolutions of the Celestial Spheres), published just before his death in 1543, is often regarded as the starting point of modern astronomy and the defining epiphany that began the scientific revolution. His heliocentric model, with the Sun at the center of the universe, demonstrated that the observed motions of celestial objects can be explained without putting Earth at rest in the center of the universe. His work stimulated further scientific investigations, becoming a landmark in the history of science that is often referred to as the Copernican Revolution. Among the great polymaths of the Renaissance, Copernicus was a mathematician, astronomer, physician, quadrilingual polyglot, classical scholar, translator, artist, Catholic cleric, jurist, governor, military leader, diplomat and economist. Among his many responsibilities, astronomy figured as little more than an avocation – yet it was in that field that he made his mark upon the world.
TopicsWikiProjectsThings to do
Related portalsAssociated WikimediaThe following Wikimedia Foundation sister projects provide more on this subject:
Discover Wikipedia using portals |