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G-dwarf Problem
In astronomy, the G-dwarf problem refers to the apparent discrepancy in the distribution of metallicity levels in stars of different stellar population, populations as compared to closed box models of galactic chemical evolution. According to closed box models, which represent galaxies without outside non-metallic material inflow, the distribution of metallicity levels in stars should follow a logarithmic curve. This amounts to high and low mass stars having the least metallicity, with G-type stars inbetween. However, these models are inconsistent with Milky Way observations. Other galaxies have been shown to have the same problem. The name comes from G-type main sequence star, G-type stars, which are bright enough to be studied easily, yet are most often found main sequence star, unevolved. This provides an extensive look at relatively young stars. Despite this, the G-dwarf problem has also been observed in K star, K and M dwarfs (the M dwarf problem). See also * Solar analog * L ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Morgan-Keenan Spectral Classification
In astronomy, stellar classification is the classification of stars based on their stellar spectrum, spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a Prism (optics), prism or diffraction grating into a spectrum exhibiting the Continuum (spectrum), rainbow of colors interspersed with spectral lines. Each line indicates a particular chemical element or molecule, with the line strength indicating the abundance of that element. The strengths of the different spectral lines vary mainly due to the temperature of the photosphere, although in some cases there are true abundance differences. The ''spectral class'' of a star is a short code primarily summarizing the ionization state, giving an objective measure of the photosphere's temperature. Most stars are currently classified under the Morgan–Keenan (MK) system using the letters ''O'', ''B'', ''A'', ''F'', ''G'', ''K'', and ''M'', a sequence from the hottest (''O'' type) to the cool ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
M Dwarf
A red dwarf is the smallest kind of star on the main sequence. Red dwarfs are by far the most common type of fusing star in the Milky Way, at least in the neighborhood of the Sun. However, due to their low luminosity, individual red dwarfs are not easily observed. Not one star that fits the stricter definitions of a red dwarf is visible to the naked eye. Proxima Centauri, the star nearest to the Sun, is a red dwarf, as are fifty of the sixty nearest stars. According to some estimates, red dwarfs make up three-quarters of the fusing stars in the Milky Way. The coolest red dwarfs near the Sun have a surface temperature of about and the smallest have radii about 9% that of the Sun, with masses about 7.5% that of the Sun. These red dwarfs have spectral types of L0 to L2. There is some overlap with the properties of brown dwarfs, since the most massive brown dwarfs at lower metallicity can be as hot as and have late M spectral types. Definitions and usage of the term "red dwar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stellar Astronomy
Astronomy is a natural science that studies astronomical object, celestial objects and the phenomena that occur in the cosmos. It uses mathematics, physics, and chemistry in order to explain their origin and their overall chronology of the Universe, evolution. Objects of interest include planets, natural satellite, moons, stars, nebulae, galaxy, galaxies, meteoroids, asteroids, and comets. Relevant phenomena include supernova explosions, gamma ray bursts, quasars, blazars, pulsars, and cosmic microwave background radiation. More generally, astronomy studies everything that originates beyond atmosphere of Earth, Earth's atmosphere. Cosmology is a branch of astronomy that studies the universe as a whole. Astronomy is one of the oldest natural sciences. The early civilizations in recorded history made methodical observations of the night sky. These include the Egyptian astronomy, Egyptians, Babylonian astronomy, Babylonians, Greek astronomy, Greeks, Indian astronomy, Indians, Ch ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
G-type Main-sequence Star
A G-type main-sequence star (spectral type: G-V), also often, and imprecisely, called a yellow dwarf, or G star, is a main sequence, main-sequence star (luminosity class V) of stellar classification, spectral type G. Such a star has about 0.9 to 1.1 solar masses and an effective temperature between about . Like other main-sequence stars, a G-type main-sequence star converts the Chemical element, element hydrogen to helium in its core by means of nuclear fusion. The Sun, the star in the center of the Solar System to which the Earth is gravitationally bound, is an example of a G-type main-sequence star (G2V type). Each second, the Sun fuses approximately 600 million tons of hydrogen into helium in a process known as the proton–proton chain (4 hydrogens form 1 helium), Mass–energy equivalence, converting about 4 million tons of matter to energy. Besides the Sun, other well-known examples of G-type main-sequence stars include Alpha Centauri, Tau Ceti, and 51 Pegasi. Description Th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Main Sequence
In astronomy, the main sequence is a classification of stars which appear on plots of stellar color index, color versus absolute magnitude, brightness as a continuous and distinctive band. Stars on this band are known as main-sequence stars or dwarf stars, and positions of stars on and off the band are believed to indicate their physical properties, as well as their progress through several types of star life-cycles. These are the most numerous true stars in the universe and include the Sun. Color-magnitude plots are known as Hertzsprung–Russell diagrams after Ejnar Hertzsprung and Henry Norris Russell. After condensation and ignition of a star, it generates thermal energy in its dense stellar core, core region through nuclear fusion of hydrogen into helium. During this stage of the star's lifetime, it is located on the main sequence at a position determined primarily by its mass but also based on its chemical composition and age. The cores of main-sequence stars are in hydros ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
List Of Nearest Stars And Brown Dwarfs
This list covers all known stars, white dwarfs, brown dwarfs, and sub-brown dwarfs within of the Sun. So far, 131 such objects have been found. Only List of nearest bright stars, 22 are bright enough to be visible without a telescope, for which the star's visible light needs to reach or exceed the dimmest brightness visible to the naked eye from Earth, which is typically around 6.5 apparent magnitude. The known 131 objects are bound in 94 stellar systems. Of those, 103 are main sequence stars: 80 red dwarfs and 23 "typical" stars having greater mass. Additionally, astronomers have found 6 white dwarfs (stars that have exhausted all fusible hydrogen), 21 brown dwarfs, as well as 1 sub-brown dwarf, WISE 0855−0714 (possibly a rogue planet). The closest system is Alpha Centauri, with Proxima Centauri as the closest star in that system, at 4.2465 light-years from Earth. The brightest, most massive and most luminous object among those 131 is Sirius A, which is also the brightest s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
List Of Nearest Bright Stars
The following nearest bright stars are found within of the closest star, the Sun, and have an absolute magnitude of +8.5 or brighter, which is approximately comparable to a listing of stars more luminous than a red dwarf. Right ascension and declination coordinates are for the epoch J2000. The distance measurements are based on the Hipparcos Catalogue and other astrometric data. In the event of a spectroscopic binary, the combined spectral type and absolute magnitude are listed in ''italics''. The list is ordered by increasing distance. Stars within 10 parsecs These stars are estimated to be within 32.6 light-years of the Sun. Stars between 10 and 13 parsecs These stars are estimated to be from 32.7 to 42.4 light years distant from the Sun. Stars between 13 and 15 parsecs These stars are estimated to be from 42.5 to 48.9 light years distant from the Sun. A value of 48.9 light years corresponds to a minimum parallax of 66.7 mas. See also * Lists of astro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Solar Analog
Solar-type stars, solar analogs (also analogues), and solar twins are stars that are particularly similar to the Sun. The stellar classification is a hierarchy with solar twin being most like the Sun followed by solar analog and then solar-type. Observations of these stars are important for understanding better the properties of the Sun in relation to other stars and the habitability of planets. By similarity to the Sun Defining the three categories by their similarity to the Sun reflects the evolution of astronomical observational techniques. Originally, solar-type was the closest that similarity to the Sun could be defined. Later, more precise measurement techniques and improved observatories allowed for greater precision of key details like temperature, enabling the creation of a solar analog category for stars that were particularly similar to the Sun. Later still, continued improvements in precision allowed for the creation of a solar-twin category for near-perfect matches ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
K Star
In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the rainbow of colors interspersed with spectral lines. Each line indicates a particular chemical element or molecule, with the line strength indicating the abundance of that element. The strengths of the different spectral lines vary mainly due to the temperature of the photosphere, although in some cases there are true abundance differences. The ''spectral class'' of a star is a short code primarily summarizing the ionization state, giving an objective measure of the photosphere's temperature. Most stars are currently classified under the Morgan–Keenan (MK) system using the letters ''O'', ''B'', ''A'', ''F'', ''G'', ''K'', and ''M'', a sequence from the hottest (''O'' type) to the coolest (''M'' type). Each letter class is then subdivided ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Astronomy
Astronomy is a natural science that studies celestial objects and the phenomena that occur in the cosmos. It uses mathematics, physics, and chemistry in order to explain their origin and their overall evolution. Objects of interest include planets, natural satellite, moons, stars, nebulae, galaxy, galaxies, meteoroids, asteroids, and comets. Relevant phenomena include supernova explosions, gamma ray bursts, quasars, blazars, pulsars, and cosmic microwave background radiation. More generally, astronomy studies everything that originates beyond atmosphere of Earth, Earth's atmosphere. Cosmology is a branch of astronomy that studies the universe as a whole. Astronomy is one of the oldest natural sciences. The early civilizations in recorded history made methodical observations of the night sky. These include the Egyptian astronomy, Egyptians, Babylonian astronomy, Babylonians, Greek astronomy, Greeks, Indian astronomy, Indians, Chinese astronomy, Chinese, Maya civilization, M ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Main Sequence Star
Main may refer to: Geography *Main River (other), multiple rivers with the same name *Ma'in, an ancient kingdom in modern-day Yemen * Main, Iran, a village in Fars Province * Spanish Main, the Caribbean coasts of mainland Spanish territories in the 16th and 17th centuries *'' The Main'', the diverse core running through Montreal, Quebec, Canada, also separating the Two Solitudes * Main (lunar crater), located near the north pole of the Moon * Main (Martian crater) People and organizations * Main (surname), a list of people with this family name *Main, alternate spelling for the Minaeans, an ancient people of modern-day Yemen * Main (band), a British ambient band formed in 1991 * Chas. T. Main, an American engineering and hydroelectric company founded in 1893 *MAIN (Mountain Area Information Network), former operator of WPVM-LP (MAIN-FM) in Asheville, North Carolina, U.S. * Main Deli Steak House ("The Main"), a smoked-meat delicatessen in Montreal, Quebec, Canada Ship ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
G-type Main Sequence Star
A G-type main-sequence star (spectral type: G-V), also often, and imprecisely, called a yellow dwarf, or G star, is a main-sequence star (luminosity class V) of spectral type G. Such a star has about 0.9 to 1.1 solar masses and an effective temperature between about . Like other main-sequence stars, a G-type main-sequence star converts the element hydrogen to helium in its core by means of nuclear fusion. The Sun, the star in the center of the Solar System to which the Earth is gravitationally bound, is an example of a G-type main-sequence star (G2V type). Each second, the Sun fuses approximately 600 million tons of hydrogen into helium in a process known as the proton–proton chain (4 hydrogens form 1 helium), converting about 4 million tons of matter to energy. Besides the Sun, other well-known examples of G-type main-sequence stars include Alpha Centauri, Tau Ceti, and 51 Pegasi. Description The term ''yellow dwarf'' is a misnomer, because G-type stars actually range in co ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
