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Bolometric Magnitude
ABSOLUTE MAGNITUDE is a measure of the luminosity of a celestial object , on a logarithmic astronomical magnitude scale. An object's absolute magnitude is defined to be equal to the apparent magnitude that the object would have if were viewed from a distance of exactly 10 parsecs (32.6 light years ), with no extinction (or dimming) of its light due to absorption by interstellar dust particles. By hypothetically placing all objects at a standard reference distance from the observer, their luminosities can be directly compared on a magnitude scale. As with all astronomical magnitudes , the absolute magnitude can be specified for different wavelength ranges corresponding to specified filter bands or passbands ; for stars a commonly quoted absolute magnitude is the ABSOLUTE VISUAL MAGNITUDE, which uses the visual (V) band of the spectrum (in the UBV photometric system )
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Elliptical Galaxy M87
MESSIER 87 (also known as VIRGO A or NGC 4486, and generally abbreviated to M87) is a supergiant elliptical galaxy in the constellation Virgo . One of the most massive galaxies in the local universe, it is notable for its large population of globular clusters —M87 contains about 12,000 compared to the 150–200 orbiting the Milky Way —and its jet of energetic plasma that originates at the core and extends outward at least 1,500 parsecs (4,900 light-years), travelling at relativistic speed . It is one of the brightest radio sources in the sky, and is a popular target for both amateur astronomy observations and professional astronomy study. French astronomer Charles Messier
Charles Messier
discovered M87 in 1781, cataloguing it as a nebulous feature while searching for objects that would confuse comet hunters
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Fifth Magnitude Star
The APPARENT MAGNITUDE (M) of a celestial object is a number that is a measure of its brightness as seen by an observer on Earth. The brighter an object appears, the lower its magnitude value (i.e. inverse relation). The Sun, at apparent magnitude of −27, is the brightest object in the sky. It is adjusted to the value it would have in the absence of the atmosphere . Furthermore, the magnitude scale is logarithmic ; a difference of one in magnitude corresponds to a change in brightness by a factor of 5√100, or about 2.512. The measurement of apparent magnitudes or brightnesses of celestial objects is known as photometry . Apparent magnitudes are used to quantify the brightness of sources at ultraviolet , visible , and infrared wavelengths. An apparent magnitude is usually measured in a specific passband corresponding to some photometric system such as the UBV system
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Dark Nebula
A DARK NEBULA or ABSORPTION NEBULA is a type of interstellar cloud that is so dense that it obscures the light from objects behind it, such as background stars and emission or reflection nebulae. The extinction of the light is caused by interstellar dust grains located in the coldest, densest parts of larger molecular clouds . Clusters and large complexes of dark nebulae are associated with Giant Molecular Clouds. Isolated small dark nebulae are called Bok globules . Like other interstellar dust or material, things it obscures are only visible using radio waves in radio astronomy or infrared in infrared astronomy . Dark clouds appear so because of sub-micrometre-sized dust particles, coated with frozen carbon monoxide and nitrogen, which effectively block the passage of light at visible wavelengths
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General Relativity
GENERAL RELATIVITY (GR, also known as the GENERAL THEORY OF RELATIVITY or GTR) is the geometric theory of gravitation published by Albert Einstein
Albert Einstein
in 1915 and the current description of gravitation in modern physics . General relativity
General relativity
is considered probably the most beautiful of all existing physical theories. General relativity generalizes special relativity and Newton\'s law of universal gravitation , providing a unified description of gravity as a geometric property of space and time , or spacetime . In particular, the curvature of spacetime is directly related to the energy and momentum of whatever matter and radiation are present. The relation is specified by the Einstein field equations , a system of partial differential equations
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Cosmological Redshift
HUBBLE\'S LAW is the name for the observation in physical cosmology that: * Objects observed in deep space (extragalactic space, 10 megaparsecs (Mpc) or more) are found to have a Doppler shift interpretable as relative velocity away from Earth ; * This Doppler-shift-measured velocity, of various galaxies receding from the Earth, is approximately proportional to their distance from the Earth for galaxies up to a few hundred megaparsecs away. Hubble's law is considered the first observational basis for the expansion of the universe and today serves as one of the pieces of evidence most often cited in support of the Big Bang model. The motion of astronomical objects due solely to this expansion is known as the HUBBLE FLOW
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Sirius
SIRIUS (/ˈsɪri.əs/ , a romanization of Greek Σείριος, Seirios, lit. "glowing" or "scorching") is a star system and the brightest star in the Earth's night sky. With a visual apparent magnitude of −1.46, it is almost twice as bright as Canopus
Canopus
, the next brightest star. The system has the Bayer designation
Bayer designation
Alpha Canis Majoris (α CMa). What the naked eye perceives as a single star is a binary star system, consisting of a white main-sequence star of spectral type A1V, termed SIRIUS A, and a faint white dwarf companion of spectral type DA2, called SIRIUS B. The distance separating Sirius A from its companion varies between 8.2 and 31.5 AU . Sirius
Sirius
appears bright because of its intrinsic luminosity and its proximity to Earth
Earth

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Betelgeuse
Coordinates : 05h 55m 10.3053s, +07° 24′ 25.426″ This orange blob shows the nearby star Betelgeuse, as seen by the Atacama Large Millimeter/submillimeter Array (ALMA). This is the first time that ALMA has ever observed the surface of a star and this first attempt has resulted in the highest-resolution image of Betelgeuse available. BETELGEUSE, also designated ALPHA ORIONIS (α ORIONIS, abbreviated ALPHA ORI, α ORI), is the ninth-brightest star in the night sky and second-brightest in the constellation of Orion . Distinctly reddish, it is a semiregular variable star whose apparent magnitude varies between 0.0 and 1.3, the widest range of any first-magnitude star . Betelgeuse
Betelgeuse
is one of three stars that make up the Winter Triangle asterism, and it marks the center of the Winter Hexagon . It would be the brightest star in the night sky if the human eye could view all wavelengths of radiation
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Planet
Shown in order from the Sun
Sun
and in true color. Sizes are not to scale. A PLANET is an astronomical body orbiting a star or stellar remnant that * is massive enough to be rounded by its own gravity , * is not massive enough to cause thermonuclear fusion , and * has cleared its neighbouring region of planetesimals . The term planet is ancient, with ties to history, astrology , science, mythology , and religion. Several planets in the Solar System can be seen with the naked eye. These were regarded by many early cultures as divine, or as emissaries of deities . As scientific knowledge advanced, human perception of the planets changed, incorporating a number of disparate objects. In 2006, the International Astronomical Union
International Astronomical Union
(IAU) officially adopted a resolution defining planets within the Solar System
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Rigel
RIGEL, also designated BETA ORIONIS (β ORIONIS, abbreviated BETA ORI, β ORI), is generally the seventh-brightest star in the night sky and the brightest star in the constellation of Orion —though periodically it is outshone within the constellation by the variable Betelgeuse . With a visual magnitude of 0.13, it is a remote and luminous star some 863 light-years distant from Earth. The star as seen from Earth is actually a multiple star system of three to five stars, the primary star being ( Rigel
Rigel
A) a blue-white supergiant which is estimated to be anywhere from 120,000 to 279,000 times as luminous as the Sun
Sun
, depending on the method used to calculate its properties. It has exhausted its core of hydrogen and swollen out to between 79 and 115 times the Sun's radius. It pulsates quasi-periodically and is classified as an Alpha Cygni variable
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Deneb
DENEB (/ˈdɛnɛb/ ), also designated α CYGNI (Latinised ALPHA CYGNI, abbreviated ALPHA CYG, α CYG), is the brightest star in the constellation of Cygnus . It is one of the vertices of the asterism known as the Summer Triangle and forms the 'head' of the Northern Cross . It is the 19th brightest star in the night sky , with an apparent magnitude of 1.25. A blue-white supergiant , Deneb
Deneb
is also one of the most luminous stars
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Zeta Puppis
ZETA PUPPIS (ζ PUPPIS, abbreviated ZETA PUP, ζ PUP), also named NAOS, is a star in the constellation of Puppis . The spectral class of O4 means this is one of the hottest, and most luminous, stars visible to the naked eye. It is one of the sky's few naked-eye class O-type stars as well as one of the closest to Earth . It is a blue supergiant , one of the most luminous stars in the Milky Way . Visually it is over 10,000 times brighter than the Sun , but its high temperature means that most of its radiation is in the ultraviolet and its bolometric luminosity is over 500,000 times that of the Sun. It is also the 62nd brightest star in terms of apparent magnitude from Earth. Naos is typical of O-type stars in having an extremely strong stellar wind , measured at 2,500 km/s, which sees the star shed more than a millionth of its mass each year, or about 10 million times that shed by the Sun over a comparable time period
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K Correction
K CORRECTION is a correction to an astronomical object's magnitude (or equivalently, its flux ) that allows a measurement of a quantity of light from an object at a redshift z to be converted to an equivalent measurement in the rest frame of the object. If one could measure all the light from an object at all wavelengths (a bolometric flux), a K correction would not be required. If one measures the light emitted in an emission line , a K-correction is not required. The need for a K-correction arises because an astronomical measurement through a single filter or a single bandpass only sees a fraction of the total spectrum , redshifted into the frame of the observer. So if the observer wants to compare the measurements through a red filter of objects at different redshifts, the observer will have to apply estimates of the K corrections to these measurements to make a comparison
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Stellar Parallax
STELLAR PARALLAX is parallax on an interstellar scale: the apparent shift of position of any nearby star (or other object) against the background of distant objects. Created by the different orbital positions of Earth, the extremely small observed shift is largest at time intervals of about six months, when Earth arrives at exactly opposite sides of the Sun
Sun
in its orbit, giving a baseline distance of about two astronomical units between observations. The parallax itself is considered to be half of this maximum, about equivalent to the observational shift that would occur due to the different positions of Earth and the Sun, a baseline of one astronomical unit (AU). Stellar parallax
Stellar parallax
is so difficult to detect that its existence was the subject of much debate in astronomy for thousands of years
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Watt
The WATT (symbol: W) is a unit of power . In the International System of Units (SI) it is defined as a derived unit of 1 joule per second , and is used to quantify the rate of energy transfer . In dimensional analysis it is described by M L 2 T 3 {displaystyle {mathsf {ML}}^{2}{mathsf {T}}^{-3}} . CONTENTS * 1 Examples * 2 Origin and adoption as an SI unit * 3 Multiples * 3.1 Femtowatt * 3.2 Picowatt * 3.3 Nanowatt * 3.4 Microwatt * 3.5 Milliwatt * 3.6 Kilowatt * 3.7 Megawatt * 3.8 Gigawatt * 3.9 Terawatt * 3.10 Petawatt * 4 Conventions in the electric power industry * 5 Radio
Radio
transmission * 6 Distinction between watts and watt-hours * 7 See also * 8 Notes * 9 References * 10 External links EXAMPLESWhen an object's velocity is held constant at one meter per second against a constant opposing force of one newton , the rate at which work is done is 1 watt
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Radiation
In physics , RADIATION is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes: * electromagnetic radiation , such as radio waves , microwaves , visible light , x-rays , and gamma radiation (γ) * particle radiation , such as alpha radiation (α) , beta radiation (β) , and neutron radiation (particles of non-zero rest energy) * acoustic radiation, such as ultrasound , sound , and seismic waves (dependent on a physical transmission medium) * gravitational radiation , radiation that takes the form of gravitational waves, or ripples in the curvature of spacetime. Radiation
Radiation
is often categorized as either ionizing or non-ionizing depending on the energy of the radiated particles. Ionizing radiation carries more than 10 eV , which is enough to ionize atoms and molecules, and break chemical bonds
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