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Red Supergiant
Red supergiants (RSGs) are stars with a supergiant luminosity class ( Yerkes class I) of spectral type K or M. They are the largest stars in the universe in terms of volume, although they are not the most massive or luminous. Betelgeuse and Antares are the brightest and best known red supergiants (RSGs), indeed the only first magnitude red supergiant stars. Classification Stars are classified as supergiants on the basis of their spectral luminosity class. This system uses certain diagnostic spectral lines to estimate the surface gravity of a star, hence determining its size relative to its mass. Larger stars are more luminous at a given temperature and can now be grouped into bands of differing luminosity. The luminosity differences between stars are most apparent at low temperatures, where giant stars are much brighter than main-sequence stars. Supergiants have the lowest surface gravities and hence are the largest and brightest at a particular temperature. The ''Yerkes'' o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Star
A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sky, night, but their immense distances from Earth make them appear as fixed stars, fixed points of light. The most prominent stars have been categorised into constellations and asterism (astronomy), 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 to stars. Only about 4,000 of these stars are visible to the naked eye, all within the Milky Way galaxy. A star's life star formation, begins with the gravitational collapse of a gaseous nebula of material composed primarily of hydrogen, along with helium and trace amounts of heavier elements. Its stellar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dwarf (star)
A dwarf star is a star of relatively small size and low luminosity. Most main sequence stars are dwarf stars. The meaning of the word "dwarf" was later extended to some star-sized objects that are not stars, and compact stellar remnants which are no longer stars. History The term was originally coined in 1906 when the Danish astronomer Ejnar Hertzsprung noticed that the reddest stars – classified as K and M in the Harvard scheme – could be divided into two distinct groups. They are either much brighter than the Sun, or much fainter. To distinguish these groups, he called them "giant" and "dwarf" stars, the dwarf stars being fainter and the giants being brighter than the Sun. Most stars are currently classified under the ''Morgan Keenan System'' using the letters O, B, A, F, G, K, and M, a sequence from the hottest: '' type O'', to the coolest: '' type M''. With the development of infrared astronomy in the late 20th century the Morgan Keenan system was extende ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hayashi Limit
Hayashi limit is a theoretical constraint upon the maximum radius of a star for a given mass. When a star is fully within hydrostatic equilibrium—a condition where the inward force of gravity is matched by the outward pressure of the gas—the star can not exceed the radius defined by the Hayashi limit. This has important implications for the evolution of a star, both during the formulative contraction period and later when the star has consumed most of its hydrogen supply through nuclear fusion. A Hertzsprung-Russell diagram displays a plot of a star's surface temperature against the luminosity. On this diagram, the Hayashi limit forms a nearly vertical line at about 3,500 K. The outer layers of low temperature stars are always convective, and models of stellar structure for fully convective stars do not provide a solution to the right of this line. Thus in theory, stars are constrained to remain to the left of this limit during all periods when they are in hydrostatic equilibri ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Epsilon Pegasi
Epsilon Pegasi ( Latinised from ε Pegasi, abbreviated Epsilon Peg, ε Peg), formally named Enif , is the brightest star in the northern constellation of Pegasus. With an average apparent visual magnitude of 2.4, this is a second-magnitude star that is readily visible to the naked eye. The distance to this star can be estimated using parallax measurements from the Hipparcos astrometry satellite, yielding a value of around . Nomenclature ''ε Pegasi'' (Latinised to ''Epsilon Pegasi'') is the star's Bayer designation. It bore the traditional name ''Enif'' derived from the Arabic word for 'nose', due to its position as the muzzle of Pegasus. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 included a table of the first two batches of names approved by the WGSN; which included ''Enif'' for this star. Other traditional names for the star i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Alpha Herculis
Alpha Herculis (α Herculis, abbreviated Alpha Her, α Her), also designated 64 Herculis, is a multiple star system in the constellation of Hercules. Appearing as a single point of light to the naked eye, it is resolvable into a number of components through a telescope. It has a combined apparent magnitude of 3.08, although the brightest component is variable in brightness. Based on parallax measurements obtained during the Hipparcos mission, it is approximately 360 light-years (110 parsecs) distant from the Sun. System Alpha Herculis is a triple star system. The primary (brightest) of the three stars, designated α1 Herculis or α Herculis A, is a pulsating variable star on the asymptotic giant branch (AGB), and is the second nearest AGB star after Mira. The primary star forms a visual binary pair with a second star, which is itself a spectroscopic binary. Alpha Herculis also forms the A and B components of a wider system designated WDS J17146+1423, with ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kelvin
The kelvin, symbol K, is the primary unit of temperature in the International System of Units (SI), used alongside its prefixed forms and the degree Celsius. It is named after the Belfast-born and University of Glasgow-based engineer and physicist William Thomson, 1st Baron Kelvin (1824–1907). The Kelvin scale is an absolute thermodynamic temperature scale, meaning it uses absolute zero as its null (zero) point. Historically, the Kelvin scale was developed by shifting the starting point of the much-older Celsius scale down from the melting point of water to absolute zero, and its increments still closely approximate the historic definition of a degree Celsius, but since 2019 the scale has been defined by fixing the Boltzmann constant to be exactly . Hence, one kelvin is equal to a change in the thermodynamic temperature that results in a change of thermal energy by . The temperature in degree Celsius is now defined as the temperature in kelvins minus 273.15, meaning t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kelvin
The kelvin, symbol K, is the primary unit of temperature in the International System of Units (SI), used alongside its prefixed forms and the degree Celsius. It is named after the Belfast-born and University of Glasgow-based engineer and physicist William Thomson, 1st Baron Kelvin (1824–1907). The Kelvin scale is an absolute thermodynamic temperature scale, meaning it uses absolute zero as its null (zero) point. Historically, the Kelvin scale was developed by shifting the starting point of the much-older Celsius scale down from the melting point of water to absolute zero, and its increments still closely approximate the historic definition of a degree Celsius, but since 2019 the scale has been defined by fixing the Boltzmann constant to be exactly . Hence, one kelvin is equal to a change in the thermodynamic temperature that results in a change of thermal energy by . The temperature in degree Celsius is now defined as the temperature in kelvins minus 273.15, meaning t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Effective Temperature
The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is often used as an estimate of a body's surface temperature when the body's emissivity curve (as a function of wavelength) is not known. When the star's or planet's net emissivity in the relevant wavelength band is less than unity (less than that of a black body), the actual temperature of the body will be higher than the effective temperature. The net emissivity may be low due to surface or atmospheric properties, including greenhouse effect. Star The effective temperature of a star is the temperature of a black body with the same luminosity per ''surface area'' () as the star and is defined according to the Stefan–Boltzmann law . Notice that the total (bolometric) luminosity of a star is then , where is the stellar radius. The definition of the stellar radius is obviously not straightf ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
HR 5171
V766 Centauri, also known as HR 5171, is a yellow hypergiant in the constellation Centaurus, either 5,000 or 12,000 light years from Earth. It is said to be either an extreme red supergiant (RSG) or recent post-red supergiant (Post-RSG) yellow hypergiant (YHG), both of which suggest it is one of the largest known stars. The star's diameter is uncertain but likely to be between 1,100 and 1,600 times that of the Sun. It was previously thought to be a contact binary, sharing a common envelope of material with a smaller yellow supergiant and secondary star, the two orbiting each other every 1,304 ± 6 days. However this has since been deemed unlikely. An optical companion, HR 5171B, may or may not be at the same distance as the yellow supergiant. System The HR 5171 system contains at least three stars. The primary A is an eclipsing binary (components Aa and Ab, or A and C in the Catalog of Components of Double and Multiple Stars) with two yellow stars in contact ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Yellow Hypergiant
A yellow hypergiant (YHG) is a massive star with an extended atmosphere, a spectral class from A to K, and, starting with an initial mass of about 20–60 solar masses, has lost as much as half that mass. They are amongst the most visually luminous stars, with absolute magnitude (MV) around −9, but also one of the rarest, with just 20 known in the Milky Way and six of those in just a single cluster. They are sometimes referred to as cool hypergiants in comparison with O- and B-type stars, and sometimes as warm hypergiants in comparison with red supergiants. Classification The term "hypergiant" was used as early as 1929, but not for the stars currently known as hypergiants. Hypergiants are defined by their '0' luminosity class, and are higher in luminosity than the brightest supergiants of class Ia, although they were not referred to as hypergiants until the late 1970s. Another criterion for hypergiants was also suggested in 1979 for some other highly luminous mass-losing hot ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Zeta Cephei
Zeta Cephei (ζ Cep, ζ Cephei) is a star in the constellation of Cepheus. Zeta Cephei marks the left shoulder of Cepheus, the King of Joppa (Ethiopia). It is one of the fundamental stars of the MK spectral sequence, defined as type K1.5 Ib. Zeta Cephei is an orange supergiant star with a surface temperature of 3,853 K and eight times more massive than the Sun. The luminosity of Zeta Cephei is approximately 3,600 times that of the Sun. At a distance of about 840 light-years, Zeta Cephei has an apparent magnitude (''m'') of 3.4 and an absolute magnitude (''M'') of -4.7. The star has a metallicity approximately 1.6 times that of the Sun; i.e., it contains 1.6 times as much heavy-element material as the Sun. Hekker et al. (2008) have detected a periodicity of 533 days, hinting at the possible presence of an as yet unseen companion. It is listed as a possible eclipsing binary with a very small amplitude. At the edge of the 8 to 10 solar mass () limit at which ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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