Portal:Stars
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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, fusion ceases and 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 - Photo credit: User:Mysid
VY Canis Majoris (VY CMa) is a red hypergiant star located in the constellation Canis Major. One of the largest stars and also one of the most luminous of its type, it has a radius of approximately 1,420 ± 120 solar radii (equal to a diameter of 13.2 astronomical units, or about 1,976,640,000 km), and is situated about 1.2 kiloparsecs (3,900 light-years) from Earth. VY CMa is a single star categorized as a semiregular variable and has an estimated period of 2,000 days. It has an average density of 5 to 10 mg/m3. If placed at the center of the Solar System, VY Canis Majoris's surface would extend beyond the orbit of Jupiter, although there is still considerable variation in estimates of the radius, with some making it larger than the orbit of Saturn. The first known record of VY Canis Majoris is in the star catalogue of Jérôme Lalande, on March 7, 1801. The catalogue listed VY CMa as a 7th magnitude star. Further studies on its apparent magnitude during the 19th century showed that the star has been fading since 1850. Since 1847, VY CMa has been known to be a red star. During the 19th century, observers measured at least six discrete components to VY CMa, suggesting the possibility that it is a multiple star. These discrete components are now known to be bright areas in the surrounding nebula. Visual observations in 1957 and high-resolution imaging in 1998 showed that VY CMa does not have a companion star. Selected article - Photo credit: User:LCGS Russ
A circumpolar star is a star that, as viewed from a given latitude on Earth, never sets (that is, never disappears below the horizon), due to its proximity to one of the celestial poles. Circumpolar stars are therefore visible from said location towards nearest pole for the entire night on every night of the year (and would be continuously visible throughout the day too, were they not overwhelmed by the Sun's glare). All circumpolar stars are within the circumpolar circle. This was in fact the original meaning of "Arctic Circle", before the current geographical meaning, meaning "Circle of the Bears" (Ursa Major, the Great Bear; and Ursa Minor, the Little Bear), from Greek αρκτικός (arktikos), "near the Bear", from the word άρκτος (arktos) bear. As Earth spins daily on its axis, the stars appear to rotate in circular paths around one of the celestial poles (the north celestial pole for observers in the Northern Hemisphere, or the south celestial pole for observers in the Southern Hemisphere). Stars far from a celestial pole appear to rotate in large circles; stars located very close to a celestial pole rotate in small circles and hence hardly seem to engage in any diurnal motion at all. Depending on the observer's latitude on Earth, some stars — the circumpolar ones — are close enough to the celestial pole to remain continuously above the horizon, while other stars dip below the horizon for some portion of their daily circular path (and others remain permanently below the horizon). The circumpolar stars appear to lie within a circle that is centered at the celestial pole and tangential to the horizon. At the Earth's North Pole, the north celestial pole is directly overhead, and all stars that are visible at all (that is, all stars in the northern celestial hemisphere) are circumpolar. As one travels south, the north celestial pole moves towards the northern horizon. More and more stars that are at a distance from it begin to disappear below the horizon for some portion of their daily "orbit", and the circle containing the remaining circumpolar stars becomes increasingly small. At the Earth's equator this circle vanishes to a single point – the celestial pole itself – which lies on the horizon, and there are therefore effectively no circumpolar stars at all. Selected image - Photo credit: IAU and Sky & Telescope magazine
Virgo is one of the constellations of the zodiac. Its name is Latin for virgin. Lying between Leo to the west and Libra to the east, it is the second largest constellation in the sky (after Hydra). It can be easily found through its brightest star, Spica. Did you know?
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Selected biography -Subrahmanyan Chandrasekhar, FRS (/ˌtʃʌndrəˈʃeɪkɑːr/ ⓘ; Tamil: சுப்பிரமணியன் சந்திரசேகர்; October 19, 1910 – August 21, 1995) was an Indian-American astrophysicist who, with William A. Fowler, won the 1983 Nobel Prize for Physics for key discoveries that led to the currently accepted theory on the later evolutionary stages of massive stars. Chandrasekhar was the nephew of Sir Chandrasekhara Venkata Raman, who won the Nobel Prize for Physics in 1930. Chandrasekhar's most notable work was the astrophysical Chandrasekhar limit. The limit describes the maximum mass of a white dwarf star, ~ 1.44 solar mass, or equivalently, the minimum mass above which a star will ultimately collapse into a neutron star or black hole (following a supernova). The limit was first calculated by Chandrasekhar in 1930 during his maiden voyage from India to Cambridge, England, for his graduate studies. In 1999, the NASA named the third of its four "Great Observatories" after Chandrasekhar. The Chandra X-ray Observatory was launched and deployed by Space Shuttle Columbia on July 23, 1999. The Chandrasekhar number, an important dimensionless number of magnetohydrodynamics, is named after him. The asteroid 1958 Chandra is also named after Chandrasekhar. American astronomer Carl Sagan, who studied Mathematics under Chandrasekhar, at the University of Chicago, praised him in the book The Demon-Haunted World: "I discovered what true mathematical elegance is from Subrahmanyan Chandrasekhar." From 1952 to 1971 Chandrasekhar also served as the editor of the Astrophysical Journal. He was awarded the Nobel Prize in Physics in 1983 for his studies on the physical processes important to the structure and evolution of stars. Chandrasekhar accepted this honor, but was upset that the citation mentioned only his earliest work, seeing it as a denigration of a lifetime's achievement. He shared it with William A. Fowler.
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