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Semiregular Variable Star
In astronomy, a semiregular variable star, a type of variable star, is a giant or supergiant of intermediate and late (cooler) spectral type showing considerable periodicity in its light changes, accompanied or sometimes interrupted by various irregularities. Periods lie in the range from 20 to more than 2000 days, while the shapes of the light curves may be rather different and variable with each cycle. The amplitudes may be from several hundredths to several magnitudes (usually 1-2 magnitudes in the V filter). Classification The semiregular variable stars have been sub-divided into four categories for many decades, with a fifth related group defined more recently. The original definitions of the four main groups were formalised in 1958 at the tenth general assembly of the International Astronomical Union (IAU). The General Catalogue of Variable Stars (GCVS) has updated the definitions with some additional information and provided newer reference stars where old examples such a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Light Curve Of Betelgeuse
Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 terahertz, between the infrared (with longer wavelengths) and the ultraviolet (with shorter wavelengths). In physics, the term "light" may refer more broadly to electromagnetic radiation of any wavelength, whether visible or not. In this sense, gamma rays, X-rays, microwaves and radio waves are also light. The primary properties of light are intensity, propagation direction, frequency or wavelength spectrum and polarization. Its speed in a vacuum, 299 792 458 metres a second (m/s), is one of the fundamental constants of nature. Like all types of electromagnetic radiation, visible light propagates by massless elementary particles called photons that represents the quanta of electromagnetic field, and can be analyzed as both waves and particl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
AG Aurigae
A&G, AG, Ag or ag may refer to Businesses and organizations * A&G Railroad (former reporting mark AG) * Action Group (Nigeria), a political party during the Nigerian First Republic * Aktiengesellschaft, a German type of corporation * Assemblies of God, the world's largest Pentecostal organization * Associated Group, a Pakistani company * Astronomische Gesellschaft, a German astronomical society * IATA code for Aruba Airlines Entertainment * '' American Gladiators'' (1989–1996 TV series) * ''American Gladiators'' (2008 TV series) Government and military * Adjutant general, the Army branch responsible for personnel * Administrator-General of South West Africa, the head of government in Namibia prior to independence in 1990 * Aerographer's mate, a rating or specialty in the US Navy that deals with weather and oceanography * American Holland-class submarine (''Amerikansky Golland''), a class of Imperial Russian submarines * Army green, the color of the US Army service unif ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
57 Pegasi
57 Pegasi is a variable binary star system in the northern constellation of Pegasus (constellation). It has the variable star designation GZ Pegasi, while ''57 Pegasi'' is the Flamsteed designation. The system is faintly visible to the naked eye as a point of light with an apparent visual magnitude that fluctuates around 5.105. It is located at a distance of approximately 780 light years from the Sun based on parallax, and is drifting further away with a radial velocity of +14 km/s. The variability of this star was discovered by J. Stebbins and C. M. Huffer in 1930. It was classified as a long-period variable of type Lb in 1974. However, based on a constant period and the shape of the light curve, it was later reclassified as a semiregular variable of type SRa in 1978. It varies in brightness from magnitude 4.95 down to 5.23 with a period of 92.66 days. The spectrum of 57 Peg displays blended features that indicate this is a binary system consisting o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Eta Geminorum
Eta Geminorum (η Geminorum, abbreviated Eta Gem, η Gem), formally named Propus , is a triple star system in the constellation of Gemini. It is a naked-eye variable star around 380 light years from the Sun. Nomenclature ''Eta Geminorum'' is the star's Bayer designation. The traditional names ''Tejat Prior'', ''Propus'' (from the Greek, meaning forward foot) and ''Praepes'' and ''Pish Pai'' (from the Persian Pīshpāy, پیشپای, meaning foreleg). 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 ''Propus'' for this star. This star, along with γ Gem (Alhena), μ Gem (Tejat Posterior), ν Gem and ξ Gem (Alzirr) were ''Al Han'ah'', "the brand" (on the neck of the camel). They also were associated in ''Al Nuḥātai'', the dual form ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
OGLE
Ogle may refer to: Places * Ogle County, Illinois, United States * Original name of Ashton, Illinois, a village * Ogle, Kentucky, United States, an unincorporated community * Ogle Township, Somerset County, Pennsylvania, United States * Ogle, Northumberland, England, a village * Ogle Castle in Northumberland, England * Glen Ogle, Scotland People * Ogle (surname) * Ogle family of Northumberland, England * Ogle Marbury (1882–1955), American jurist and politician, Chief Judge of the supreme court of Maryland * Ogle Moore (1801–1874), Irish Anglican priest Titles * Baron Ogle * Earl of Ogle Other uses * Ogle Airport, near Georgetown, Guyana * Ogle Design, a British design consultancy and onetime car maker * OGLE, the Optical Gravitational Lensing Experiment The Optical Gravitational Lensing Experiment (OGLE) is a Polish astronomical project based at the University of Warsaw that runs a long-term variability sky survey (1992–present). The main goals are the detecti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Period-luminosity Relationship
In astronomy, a period-luminosity relation is a relationship linking the luminosity of pulsating variable stars with their pulsation period. The best-known relation is the direct proportionality law holding for Classical Cepheid variables, sometimes called the Leavitt law. Discovered in 1908 by Henrietta Swan Leavitt, the relation established Cepheids as foundational indicators of cosmic benchmarks for scaling galactic and extragalactic distances. The physical model explaining the Leavitt's law for classical cepheids is called '' kappa mechanism''. History Leavitt, a graduate of Radcliffe College, worked at the Harvard College Observatory as a " computer", tasked with examining photographic plates in order to measure and catalog the brightness of stars. Observatory Director Edward Charles Pickering assigned Leavitt to the study of variable stars of the Small and Large Magellanic Clouds, as recorded on photographic plates taken with the Bruce Astrograph of the Boyden St ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gravitational Microlensing
Gravitational microlensing is an astronomical phenomenon due to the gravitational lens effect. It can be used to detect objects that range from the mass of a planet to the mass of a star, regardless of the light they emit. Typically, astronomers can only detect bright objects that emit much light (stars) or large objects that block background light (clouds of gas and dust). These objects make up only a minor portion of the mass of a galaxy. Microlensing allows the study of objects that emit little or no light. When a distant star or quasar gets sufficiently aligned with a massive compact foreground object, the bending of light due to its gravitational field, as discussed by Albert Einstein in 1915, leads to two distorted images (generally unresolved), resulting in an observable magnification. The time-scale of the transient brightening depends on the mass of the foreground object as well as on the relative proper motion between the background 'source' and the foreground 'lens ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Large Magellanic Cloud
The Large Magellanic Cloud (LMC), or Nubecula Major, is a satellite galaxy of the Milky Way. At a distance of around 50 kiloparsecs (≈160,000 light-years), the LMC is the second- or third-closest galaxy to the Milky Way, after the Sagittarius Dwarf Spheroidal (16 kpc) and the possible dwarf irregular galaxy known as the Canis Major Overdensity. Based on the D25 isophote at the B-band (445 nm wavelength of light), the Large Magellanic Cloud is approximately across. It is roughly a hundredth as massive as the Milky WayMagellanic Cloud . ''''. 2009. Encyclopædia Britannica Online. 30 Aug. 2009. and is the fourth-largest ga ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Overtone
An overtone is any resonant frequency above the fundamental frequency of a sound. (An overtone may or may not be a harmonic) In other words, overtones are all pitches higher than the lowest pitch within an individual sound; the fundamental is the lowest pitch. While the fundamental is usually heard most prominently, overtones are actually present in any pitch except a true sine wave. The relative volume or amplitude of various overtone partials is one of the key identifying features of timbre, or the individual characteristic of a sound. Using the model of Fourier analysis, the fundamental and the overtones together are called partials. Harmonics, or more precisely, harmonic partials, are partials whose frequencies are numerical integer multiples of the fundamental (including the fundamental, which is 1 times itself). These overlapping terms are variously used when discussing the acoustic behavior of musical instruments.Alexander J. Ellis (translating Hermann von Helmholtz): ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fundamental Mode
A normal mode of a dynamical system is a pattern of motion in which all parts of the system move sinusoidally with the same frequency and with a fixed phase relation. The free motion described by the normal modes takes place at fixed frequencies. These fixed frequencies of the normal modes of a system are known as its natural frequencies or resonant frequencies. A physical object, such as a building, bridge, or molecule, has a set of normal modes and their natural frequencies that depend on its structure, materials and boundary conditions. The most general motion of a system is a superposition of its normal modes. The modes are normal in the sense that they can move independently, that is to say that an excitation of one mode will never cause motion of a different mode. In mathematical terms, normal modes are orthogonal to each other. General definitions Mode In the wave theory of physics and engineering, a mode in a dynamical system is a standing wave state of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Long-period Variable
The descriptive term long-period variable star refers to various groups of cool luminous pulsating variable stars. It is frequently abbreviated to LPV. Types of variation The General Catalogue of Variable Stars does not define a long-period variable star type, although it does describe Mira variables as long-period variables. The term was first used in the 19th century, before more precise classifications of variable stars, to refer to a group that were known to vary on timescales typically hundreds of days. By the middle of the 20th century, long period variables were known to be cool giant stars. The relationship of Mira variables, semiregular variables, and other pulsating stars was being investigated and the term ''long period variable'' was generally restricted to the coolest pulsating stars, almost all Mira variables. Semiregular variables were considered intermediate between LPVs and Cepheids. After the publication of the General Catalogue of Variable Stars, both ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mira Variable
Mira variables (named for the prototype star Mira) are a class of pulsating stars characterized by very red colours, pulsation periods longer than 100 days, and amplitudes greater than one magnitude in infrared and 2.5 magnitude at visual wavelengths. They are red giants in the very late stages of stellar evolution, on the asymptotic giant branch (AGB), that will expel their outer envelopes as planetary nebulae and become white dwarfs within a few million years. Mira variables are stars massive enough that they have undergone helium fusion in their cores but are less than two solar masses, stars that have already lost about half their initial mass. However, they can be thousands of times more luminous than the Sun due to their very large distended envelopes. They are pulsating due to the entire star expanding and contracting. This produces a change in temperature along with radius, both of which factors cause the variation in luminosity. The pulsation depends on the mass a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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