Portal:Stars
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 - Photo credit: NASA
Eta Carinae (η Carinae or η Car) is a stellar system in the constellation Carina, about 7,500 to 8,000 light-years from the Sun. The system contains at least two stars, one of which is a Luminous Blue Variable (LBV), which during the early stages of its life had a mass of around 150 solar masses, of which it has lost at least 30 since. It is thought that a Wolf–Rayet star of approximately 30 solar masses exists in orbit around its larger companion star, although an enormous thick red nebula surrounding Eta Carinae makes it impossible to see optically. Its combined luminosity is about four million times that of the Sun and has an estimated system mass in excess of 100 solar masses. It is not visible north of latitude 30° N and is circumpolar south of latitude 30° S. Because of its mass and the stage of life, it is expected to explode in a supernova or even hypernova in the astronomically near future. Eta Carinae has the traditional names Tseen She (from the Chinese 天社 [Mandarin: tiānshè] "Heaven's altar") and Foramen. In Chinese, 海山 (Hǎi Shān), meaning Sea and Mountain, refers to an asterism consisting of η Carinae, s Carinae, λ Centauri and λ Muscae. This stellar system is currently one of the most massive that can be studied in great detail. Until recently, Eta Carinae was thought to be the most massive single star, but in 2005 it was realised to be a binary system. The most massive star in the Eta Carinae multiple star system has more than 100 times the mass of the Sun. Other known massive stars are more luminous and more massive. Selected article - Photo credit: JAXA/NASA
A solar flare is a large explosion in the Sun's atmosphere that can release as much as 6 × 1025 joules of energy. The term is also used to refer to similar phenomena in other stars, where the term stellar flare applies. Solar flares affect all layers of the solar atmosphere (photosphere, corona, and chromosphere), heating plasma to tens of millions of kelvins and accelerating electrons, protons, and heavier ions to near the speed of light. They produce radiation across the electromagnetic spectrum at all wavelengths, from radio waves to gamma rays. Most flares occur in active regions around sunspots, where intense magnetic fields penetrate the photosphere to link the corona to the solar interior. Flares are powered by the sudden (timescales of minutes to tens of minutes) release of magnetic energy stored in the corona. If a solar flare is exceptionally powerful, it can cause coronal mass ejections. X-rays and UV radiation emitted by solar flares can affect Earth's ionosphere and disrupt long-range radio communications. Direct radio emission at decimetric wavelengths may disturb operation of radars and other devices operating at these frequencies. Solar flares were first observed on the Sun by Richard Christopher Carrington and independently by Richard Hodgson in 1859 as localized visible brightenings of small areas within a sunspot group. Stellar flares have also been observed on a variety of other stars. The frequency of occurrence of solar flares varies, from several per day when the Sun is particularly "active" to less than one each week when the Sun is "quiet". Large flares are less frequent than smaller ones. Solar activity varies with an 11-year cycle (the solar cycle). At the peak of the cycle there are typically more sunspots on the Sun, and hence more solar flares. Selected image - Photo credit: NASA
Messier 82 (also known as NGC 3034, Cigar Galaxy or M82) is the prototypenearby starburst galaxy about 12 million light-years away in the constellation Ursa Major. The starburst galaxy is five times as bright as the whole Milky Way and one hundred times as bright as our galaxy's center. M82 was previously believed to be an irregular galaxy. However, in 2005, two symmetric spiral arms were discovered in the near-infrared (NIR) images of M82, and is now considered a spiral galaxy. Did you know?SubcategoriesTo display all subcategories click on the ►
Selected biography - Photo credit: Unknown artist, uploaded by User:ArtMechanic
Johannes Kepler (/ˈkɛplər/; German: [joˈhanəs ˈkɛplɐ, -nɛs -] ; 27 December 1571 – 15 November 1630) was a German astronomer, mathematician, astrologer, natural philosopher and writer on music. He is a key figure in the 17th-century Scientific Revolution, best known for his laws of planetary motion, and his books Astronomia nova, Harmonice Mundi, and Epitome Astronomiae Copernicanae, influencing among others Isaac Newton, providing one of the foundations for his theory of universal gravitation. The variety and impact of his work made Kepler one of the founders and fathers of modern astronomy, the scientific method, natural and modern science. He has been described as the "father of science fiction" for his novel Somnium. Kepler was a mathematics teacher at a seminary school in Graz, where he became an associate of Prince Hans Ulrich von Eggenberg. Later he became an assistant to the astronomer Tycho Brahe in Prague, and eventually the imperial mathematician to Emperor Rudolf II and his two successors Matthias and Ferdinand II. He also taught mathematics in Linz, and was an adviser to General Wallenstein. Additionally, he did fundamental work in the field of optics, being named the father of modern optics, in particular for his Astronomiae pars optica. He also invented an improved version of the refracting telescope, the Keplerian telescope, which became the foundation of the modern refracting telescope, while also improving on the telescope design by Galileo Galilei, who mentioned Kepler's discoveries in his work. Kepler lived in an era when there was no clear distinction between astronomy and astrology, but there was a strong division between astronomy (a branch of mathematics within the liberal arts) and physics (a branch of natural philosophy). Kepler also incorporated religious arguments and reasoning into his work, motivated by the religious conviction and belief that God had created the world according to an intelligible plan that is accessible through the natural light of reason. Kepler described his new astronomy as "celestial physics", as "an excursion into Aristotle's Metaphysics", and as "a supplement to Aristotle's On the Heavens", transforming the ancient tradition of physical cosmology by treating astronomy as part of a universal mathematical physics. (Full article...) TopicsThings to do
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