65-497: GA6 , GA-6 , or GA 6 may refer to: 2010 GA 6 , a micro-asteroid of the Apollo group Georgia State Route 6 , a state highway in Georgia, United States Georgia's 6th congressional district , congressional district in Georgia, United States Trumpchi GA6 , a 2014–present Chinese mid-size sedan [REDACTED] Topics referred to by
130-475: A radiation source (e.g. star) at the standard distance of 10 parsecs , it follows that the zero point of the apparent bolometric magnitude scale m bol = 0 corresponds to irradiance f 0 = 2.518 021 002 × 10 W/m . Using the IAU 2015 scale, the nominal total solar irradiance (" solar constant ") measured at 1 astronomical unit ( 1361 W/m ) corresponds to an apparent bolometric magnitude of
195-427: A diffuse flat disk of the same diameter. A quarter phase ( α = 90 ∘ {\displaystyle \alpha =90^{\circ }} ) has 1 π {\textstyle {\frac {1}{\pi }}} as much light as full phase ( α = 0 ∘ {\displaystyle \alpha =0^{\circ }} ). By contrast, a diffuse disk reflector model
260-419: A diffuse reflector. Bodies with no atmosphere, like asteroids or moons, tend to reflect light more strongly to the direction of the incident light, and their brightness increases rapidly as the phase angle approaches 0 ∘ {\displaystyle 0^{\circ }} . This rapid brightening near opposition is called the opposition effect . Its strength depends on the physical properties of
325-477: A phase angle of α = 93.0 ∘ {\displaystyle \alpha =93.0^{\circ }} (near quarter phase). Under full-phase conditions, Venus would have been visible at m = − 4.384 + 5 log 10 ( 0.719 ⋅ 0.645 ) = − 6.09. {\displaystyle m=-4.384+5\log _{10}{\left(0.719\cdot 0.645\right)}=-6.09.} Accounting for
390-518: A single filter band, as expressed on a logarithmic magnitude scale. To convert from an absolute magnitude in a specific filter band to absolute bolometric magnitude, a bolometric correction (BC) is applied. In stellar and galactic astronomy, the standard distance is 10 parsecs (about 32.616 light-years, 308.57 petameters or 308.57 trillion kilometres). A star at 10 parsecs has a parallax of 0.1″ (100 milliarcseconds ). Galaxies (and other extended objects ) are much larger than 10 parsecs; their light
455-490: A standard reference distance from the observer, their luminosities can be directly compared among each other on a magnitude scale. For Solar System bodies that shine in reflected light, a different definition of absolute magnitude (H) is used, based on a standard reference distance of one astronomical unit . Absolute magnitudes of stars generally range from approximately −10 to +20. The absolute magnitudes of galaxies can be much lower (brighter). The more luminous an object,
520-631: A threat to a town or city. There are no projection of future close approaches to Earth available. According to NASA astronomers, 2010 GA 6 measures approximately 22 meters (72 ft) in diameter. Based on a generic magnitude-to-diameter conversion, the asteroid measures between 19 and 36 meters in diameter, for an absolute magnitude of 22.6, and an assumed albedo between 0.057 and 0.20, which represent typical values for carbonaceous and stony asteroids, respectively. This minor planet has neither been numbered nor named . Absolute magnitude In astronomy , absolute magnitude ( M )
585-422: A value close to that, m 1 = + 0.5 {\displaystyle m_{1}=+0.5} . The absolute magnitude of any given comet can vary dramatically. It can change as the comet becomes more or less active over time or if it undergoes an outburst. This makes it difficult to use the absolute magnitude for a size estimate. When comet 289P/Blanpain was discovered in 1819, its absolute magnitude
650-716: A visual magnitude m V of 0.12 and distance of about 860 light-years: M V = 0.12 − 5 ( log 10 860 3.2616 − 1 ) = − 7.0. {\displaystyle M_{\mathrm {V} }=0.12-5\left(\log _{10}{\frac {860}{3.2616}}-1\right)=-7.0.} Vega has a parallax p of 0.129″, and an apparent magnitude m V of 0.03: M V = 0.03 + 5 ( log 10 0.129 + 1 ) = + 0.6. {\displaystyle M_{\mathrm {V} }=0.03+5\left(\log _{10}{0.129}+1\right)=+0.6.} The Black Eye Galaxy has
715-414: A visual magnitude m V of 9.36 and a distance modulus μ of 31.06: M V = 9.36 − 31.06 = − 21.7. {\displaystyle M_{\mathrm {V} }=9.36-31.06=-21.7.} The absolute bolometric magnitude ( M bol ) takes into account electromagnetic radiation at all wavelengths . It includes those unobserved due to instrumental passband ,
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#1732887167265780-539: Is a measure of the luminosity of a celestial object on an inverse logarithmic astronomical magnitude scale; the more luminous (intrinsically bright) an object, the lower its magnitude number. An object's absolute magnitude is defined to be equal to the apparent magnitude that the object would have if it were viewed from a distance of exactly 10 parsecs (32.6 light-years ), without extinction (or dimming) of its light due to absorption by interstellar matter and cosmic dust . By hypothetically placing all objects at
845-446: Is an Apollo asteroid . Apollo's cross the orbit of Earth and are the largest group of near-Earth objects with nearly 10 thousand known members. It orbits the Sun in the inner main-belt at a distance of 0.93–3.69 AU once every 3 years and 6 months (1,281 days; semi-major axis of 2.31 AU). Its orbit has a high eccentricity of 0.60 and an inclination of 10 ° with respect to
910-565: Is assumed that extinction from gas and dust is negligible. Typical extinction rates within the Milky Way galaxy are 1 to 2 magnitudes per kiloparsec, when dark clouds are taken into account. For objects at very large distances (outside the Milky Way) the luminosity distance d L (distance defined using luminosity measurements) must be used instead of d , because the Euclidean approximation
975-1669: Is based on the diffuse disk reflector model. The absolute magnitude H {\displaystyle H} , diameter D {\displaystyle D} (in kilometers ) and geometric albedo p {\displaystyle p} of a body are related by D = 1329 p × 10 − 0.2 H k m , {\displaystyle D={\frac {1329}{\sqrt {p}}}\times 10^{-0.2H}\mathrm {km} ,} or equivalently, H = 5 log 10 1329 D p . {\displaystyle H=5\log _{10}{\frac {1329}{D{\sqrt {p}}}}.} Example: The Moon's absolute magnitude H {\displaystyle H} can be calculated from its diameter D = 3474 km {\displaystyle D=3474{\text{ km}}} and geometric albedo p = 0.113 {\displaystyle p=0.113} : H = 5 log 10 1329 3474 0.113 = + 0.28. {\displaystyle H=5\log _{10}{\frac {1329}{3474{\sqrt {0.113}}}}=+0.28.} We have d B S = 1 AU {\displaystyle d_{BS}=1{\text{ AU}}} , d B O = 384400 km = 0.00257 AU . {\displaystyle d_{BO}=384400{\text{ km}}=0.00257{\text{ AU}}.} At quarter phase , q ( α ) ≈ 2 3 π {\textstyle q(\alpha )\approx {\frac {2}{3\pi }}} (according to
1040-418: Is changing slowly due to seasonal effects as the planet moves along its 165-year orbit around the Sun, and the approximation above is only valid after the year 2000. For some circumstances, like α ≥ 179 ∘ {\displaystyle \alpha \geq 179^{\circ }} for Venus, no observations are available, and the phase curve is unknown in those cases. The formula for
1105-536: Is close to the value of m = − 4.62 {\displaystyle m=-4.62} predicted by the Jet Propulsion Laboratory. Example 2: At first quarter phase , the approximation for the Moon gives − 2.5 log 10 q ( 90 ∘ ) = 2.71. {\textstyle -2.5\log _{10}{q(90^{\circ })}=2.71.} With that,
1170-622: Is different from Wikidata All article disambiguation pages All disambiguation pages 2010 GA6 2010 GA 6 is a micro- asteroid on an eccentric orbit, classified as a near-Earth object of the Apollo group . It was first observed on 5 April 2010, by astronomers of the Catalina Sky Survey at Mount Lemmon Observatory , Arizona, United States, four days before a close approach to Earth at 1.1 lunar distances on 9 April 2010. It has not been observed since. 2010 GA 6
1235-460: Is impossible in practice). Because Solar System bodies are illuminated by the Sun, their brightness varies as a function of illumination conditions, described by the phase angle . This relationship is referred to as the phase curve . The absolute magnitude is the brightness at phase angle zero, an arrangement known as opposition , from a distance of one AU. The absolute magnitude H {\displaystyle H} can be used to calculate
1300-400: Is invalid for distant objects. Instead, general relativity must be taken into account. Moreover, the cosmological redshift complicates the relationship between absolute and apparent magnitude, because the radiation observed was shifted into the red range of the spectrum. To compare the magnitudes of very distant objects with those of local objects, a K correction might have to be applied to
1365-455: Is notably larger than the nominal distance of its 2010-flyby. On 9 April 2010, 02:07 UT, the asteroid passed Earth at a nominal distance of 434,000 km; 270,000 mi (0.0029 AU) or 1.1 lunar distances . A stony asteroid 22 meters in diameter can be expected to create an air burst with the equivalent of 300 kilotons of TNT at an altitude of 21 kilometers (69,000 ft). Generally only asteroids larger than 35 meters across pose
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#17328871672651430-443: Is radiated over an extended patch of sky, and their overall brightness cannot be directly observed from relatively short distances, but the same convention is used. A galaxy's magnitude is defined by measuring all the light radiated over the entire object, treating that integrated brightness as the brightness of a single point-like or star-like source, and computing the magnitude of that point-like source as it would appear if observed at
1495-434: Is simply q ( α ) = cos α {\displaystyle q(\alpha )=\cos {\alpha }} , which isn't realistic, but it does represent the opposition surge for rough surfaces that reflect more uniform light back at low phase angles. The definition of the geometric albedo p {\displaystyle p} , a measure for the reflectivity of planetary surfaces,
1560-462: Is somewhat lower than that, m = − 10.0. {\displaystyle m=-10.0.} This is not a good approximation, because the phase curve of the Moon is too complicated for the diffuse reflector model. A more accurate formula is given in the following section. Because Solar System bodies are never perfect diffuse reflectors, astronomers use different models to predict apparent magnitudes based on known or assumed properties of
1625-594: Is still brighter than the Sun , whose absolute visual magnitude is 4.83. The Sun's absolute bolometric magnitude is set arbitrarily, usually at 4.75. Absolute magnitudes of stars generally range from approximately −10 to +20. The absolute magnitudes of galaxies can be much lower (brighter). For example, the giant elliptical galaxy M87 has an absolute magnitude of −22 (i.e. as bright as about 60,000 stars of magnitude −10). Some active galactic nuclei ( quasars like CTA-102 ) can reach absolute magnitudes in excess of −32, making them
1690-620: Is the Astronomical Unit , and K 1 , 2 {\displaystyle K_{1,2}} are the slope parameters characterising the comet's activity. For K = 2 {\displaystyle K=2} , this reduces to the formula for a purely reflecting body (showing no cometary activity). For example, the lightcurve of comet C/2011 L4 (PANSTARRS) can be approximated by M 1 = 5.41 , K 1 = 3.69. {\displaystyle M_{1}=5.41{\text{, }}K_{1}=3.69.} On
1755-461: Is the absolute visual magnitude , which uses the visual (V) band of the spectrum (in the UBV photometric system ). Absolute magnitudes are denoted by a capital M, with a subscript representing the filter band used for measurement, such as M V for absolute magnitude in the V band. An object's absolute bolometric magnitude (M bol ) represents its total luminosity over all wavelengths , rather than in
1820-818: Is the phase angle , the angle between the body-Sun and body–observer lines. q ( α ) {\displaystyle q(\alpha )} is the phase integral (the integration of reflected light; a number in the 0 to 1 range). By the law of cosines , we have: cos α = d B O 2 + d B S 2 − d O S 2 2 d B O d B S . {\displaystyle \cos {\alpha }={\frac {d_{\mathrm {BO} }^{2}+d_{\mathrm {BS} }^{2}-d_{\mathrm {OS} }^{2}}{2d_{\mathrm {BO} }d_{\mathrm {BS} }}}.} Distances: The value of q ( α ) {\displaystyle q(\alpha )} depends on
1885-405: Is the comet with the smallest nucleus that has ever been physically characterised, and usually doesn't become brighter than 18 mag. For some comets that have been observed at heliocentric distances large enough to distinguish between light reflected from the coma, and light from the nucleus itself, an absolute magnitude analogous to that used for asteroids has been calculated, allowing to estimate
1950-490: Is the effective inclination of Saturn's rings (their tilt relative to the observer), which as seen from Earth varies between 0° and 27° over the course of one Saturn orbit, and ϕ ′ {\displaystyle \phi '} is a small correction term depending on Uranus' sub-Earth and sub-solar latitudes. t {\displaystyle t} is the Common Era year. Neptune's absolute magnitude
2015-529: Is the radiant flux measured at distance d (in parsecs), F 10 the radiant flux measured at distance 10 pc . Using the common logarithm , the equation can be written as M = m − 5 log 10 ( d pc ) + 5 = m − 5 ( log 10 d pc − 1 ) , {\displaystyle M=m-5\log _{10}(d_{\text{pc}})+5=m-5\left(\log _{10}d_{\text{pc}}-1\right),} where it
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2080-405: Is valid for phase angles α < 120 ∘ {\displaystyle \alpha <120^{\circ }} , and works best when α < 20 ∘ {\displaystyle \alpha <20^{\circ }} . The slope parameter G {\displaystyle G} relates to the surge in brightness, typically 0.3 mag , when
2145-586: The H G {\displaystyle HG} -system was officially replaced by an improved system with three parameters H {\displaystyle H} , G 1 {\displaystyle G_{1}} and G 2 {\displaystyle G_{2}} , which produces more satisfactory results if the opposition effect is very small or restricted to very small phase angles. However, as of 2022, this H G 1 G 2 {\displaystyle HG_{1}G_{2}} -system has not been adopted by either
2210-715: The International Astronomical Union passed Resolution B2 defining the zero points of the absolute and apparent bolometric magnitude scales in SI units for power ( watts ) and irradiance (W/m ), respectively. Although bolometric magnitudes had been used by astronomers for many decades, there had been systematic differences in the absolute magnitude-luminosity scales presented in various astronomical references, and no international standardization. This led to systematic differences in bolometric corrections scales. Combined with incorrect assumed absolute bolometric magnitudes for
2275-494: The Minor Planet Center . m = H + 5 log 10 ( d B S d B O d 0 2 ) − 2.5 log 10 q ( α ) , {\displaystyle m=H+5\log _{10}{\left({\frac {d_{BS}d_{BO}}{d_{0}^{2}}}\right)}-2.5\log _{10}{q(\alpha )},} where This relation
2340-672: The Sun of m bol,⊙ = −26.832 . Following Resolution B2, the relation between a star's absolute bolometric magnitude and its luminosity is no longer directly tied to the Sun's (variable) luminosity: M b o l = − 2.5 log 10 L ⋆ L 0 ≈ − 2.5 log 10 L ⋆ + 71.197425 {\displaystyle M_{\mathrm {bol} }=-2.5\log _{10}{\frac {L_{\star }}{L_{0}}}\approx -2.5\log _{10}L_{\star }+71.197425} where The new IAU absolute magnitude scale permanently disconnects
2405-611: The ecliptic . With an aphelion of 3.69 AU, it is also a Mars-crossing asteroid , as it crosses the orbit of the Red Planet at 1.666 AU. With a 1-day observation arc , 2010 GA 6 had a 1 in 6 million chance of impacting Earth in 2074. It was removed from the Sentry Risk Table on 8 April 2010. The asteroid has now a minimum orbital intersection distance with Earth of 599,000 km; 372,000 mi (0.004005 AU), which corresponds to 1.6 lunar distances, and
2470-1188: The Earth's atmospheric absorption, and extinction by interstellar dust . It is defined based on the luminosity of the stars. In the case of stars with few observations, it must be computed assuming an effective temperature . Classically, the difference in bolometric magnitude is related to the luminosity ratio according to: M b o l , ⋆ − M b o l , ⊙ = − 2.5 log 10 ( L ⋆ L ⊙ ) {\displaystyle M_{\mathrm {bol,\star } }-M_{\mathrm {bol,\odot } }=-2.5\log _{10}\left({\frac {L_{\star }}{L_{\odot }}}\right)} which makes by inversion: L ⋆ L ⊙ = 10 0.4 ( M b o l , ⊙ − M b o l , ⋆ ) {\displaystyle {\frac {L_{\star }}{L_{\odot }}}=10^{0.4\left(M_{\mathrm {bol,\odot } }-M_{\mathrm {bol,\star } }\right)}} where In August 2015,
2535-482: The Minor Planet Center nor Jet Propulsion Laboratory . The apparent magnitude of asteroids varies as they rotate , on time scales of seconds to weeks depending on their rotation period , by up to 2 mag {\displaystyle 2{\text{ mag}}} or more. In addition, their absolute magnitude can vary with the viewing direction, depending on their axial tilt . In many cases, neither
2600-572: The Moon is about 0.06 mag fainter than at first quarter, because that part of its surface has a lower albedo. Earth's albedo varies by a factor of 6, from 0.12 in the cloud-free case to 0.76 in the case of altostratus cloud . The absolute magnitude in the table corresponds to an albedo of 0.434. Due to the variability of the weather , Earth's apparent magnitude cannot be predicted as accurately as that of most other planets. If an object has an atmosphere, it reflects light more or less isotropically in all directions, and its brightness can be modelled as
2665-414: The Moon is only applicable to the near side of the Moon , the portion that is visible from the Earth. Example 1: On 1 January 2019, Venus was d B S = 0.719 AU {\displaystyle d_{BS}=0.719{\text{ AU}}} from the Sun, and d B O = 0.645 AU {\displaystyle d_{BO}=0.645{\text{ AU}}} from Earth, at
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2730-524: The Sun, this could lead to systematic errors in estimated stellar luminosities (and other stellar properties, such as radii or ages, which rely on stellar luminosity to be calculated). Resolution B2 defines an absolute bolometric magnitude scale where M bol = 0 corresponds to luminosity L 0 = 3.0128 × 10 W , with the zero point luminosity L 0 set such that the Sun (with nominal luminosity 3.828 × 10 W ) corresponds to absolute bolometric magnitude M bol,⊙ = 4.74 . Placing
2795-434: The V filter band. The Sun has absolute magnitude M V = +4.83. Highly luminous objects can have negative absolute magnitudes: for example, the Milky Way galaxy has an absolute B magnitude of about −20.8. 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
2860-682: The apparent magnitude m {\displaystyle m} of a body. For an object reflecting sunlight, H {\displaystyle H} and m {\displaystyle m} are connected by the relation m = H + 5 log 10 ( d B S d B O d 0 2 ) − 2.5 log 10 q ( α ) , {\displaystyle m=H+5\log _{10}{\left({\frac {d_{BS}d_{BO}}{d_{0}^{2}}}\right)}-2.5\log _{10}{q(\alpha )},} where α {\displaystyle \alpha }
2925-419: The apparent magnitude of the Moon is m = + 0.28 + 5 log 10 ( 1 ⋅ 0.00257 ) + 2.71 = − 9.96 , {\textstyle m=+0.28+5\log _{10}{\left(1\cdot 0.00257\right)}+2.71=-9.96,} close to the expected value of about − 10.0 {\displaystyle -10.0} . At last quarter ,
2990-450: The body's surface, and hence it differs from asteroid to asteroid. In 1985, the IAU adopted the semi-empirical H G {\displaystyle HG} -system, based on two parameters H {\displaystyle H} and G {\displaystyle G} called absolute magnitude and slope , to model the opposition effect for the ephemerides published by
3055-584: The body. For planets, approximations for the correction term − 2.5 log 10 q ( α ) {\displaystyle -2.5\log _{10}{q(\alpha )}} in the formula for m have been derived empirically, to match observations at different phase angles . The approximations recommended by the Astronomical Almanac are (with α {\displaystyle \alpha } in degrees): Here β {\displaystyle \beta }
3120-772: The brightness of each star appearing in the sky. The brightest stars in the sky were assigned an apparent magnitude m = 1 , and the dimmest stars visible to the naked eye are assigned m = 6 . The difference between them corresponds to a factor of 100 in brightness. For objects within the immediate neighborhood of the Sun, the absolute magnitude M and apparent magnitude m from any distance d (in parsecs , with 1 pc = 3.2616 light-years ) are related by 100 m − M 5 = F 10 F = ( d 10 p c ) 2 , {\displaystyle 100^{\frac {m-M}{5}}={\frac {F_{10}}{F}}=\left({\frac {d}{10\;\mathrm {pc} }}\right)^{2},} where F
3185-1325: The brightness of the core region alone). Both are different scales than the magnitude scale used for planets and asteroids, and can not be used for a size comparison with an asteroid's absolute magnitude H . The activity of comets varies with their distance from the Sun. Their brightness can be approximated as m 1 = M 1 + 2.5 ⋅ K 1 log 10 ( d B S d 0 ) + 5 log 10 ( d B O d 0 ) {\displaystyle m_{1}=M_{1}+2.5\cdot K_{1}\log _{10}{\left({\frac {d_{BS}}{d_{0}}}\right)}+5\log _{10}{\left({\frac {d_{BO}}{d_{0}}}\right)}} m 2 = M 2 + 2.5 ⋅ K 2 log 10 ( d B S d 0 ) + 5 log 10 ( d B O d 0 ) , {\displaystyle m_{2}=M_{2}+2.5\cdot K_{2}\log _{10}{\left({\frac {d_{BS}}{d_{0}}}\right)}+5\log _{10}{\left({\frac {d_{BO}}{d_{0}}}\right)},} where m 1 , 2 {\displaystyle m_{1,2}} are
3250-787: The day of its perihelion passage, 10 March 2013, comet PANSTARRS was 0.302 AU {\displaystyle 0.302{\text{ AU}}} from the Sun and 1.109 AU {\displaystyle 1.109{\text{ AU}}} from Earth. The total apparent magnitude m 1 {\displaystyle m_{1}} is predicted to have been m 1 = 5.41 + 2.5 ⋅ 3.69 ⋅ log 10 ( 0.302 ) + 5 log 10 ( 1.109 ) = + 0.8 {\displaystyle m_{1}=5.41+2.5\cdot 3.69\cdot \log _{10}{\left(0.302\right)}+5\log _{10}{\left(1.109\right)}=+0.8} at that time. The Minor Planet Center gives
3315-479: The diffuse reflector model), this yields an apparent magnitude of m = + 0.28 + 5 log 10 ( 1 ⋅ 0.00257 ) − 2.5 log 10 ( 2 3 π ) = − 10.99. {\displaystyle m=+0.28+5\log _{10}{\left(1\cdot 0.00257\right)}-2.5\log _{10}{\left({\frac {2}{3\pi }}\right)}=-10.99.} The actual value
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#17328871672653380-747: The high phase angle, the correction term above yields an actual apparent magnitude of m = − 6.09 + ( − 1.044 × 10 − 3 ⋅ 93.0 + 3.687 × 10 − 4 ⋅ 93.0 2 − 2.814 × 10 − 6 ⋅ 93.0 3 + 8.938 × 10 − 9 ⋅ 93.0 4 ) = − 4.59. {\displaystyle m=-6.09+\left(-1.044\times 10^{-3}\cdot 93.0+3.687\times 10^{-4}\cdot 93.0^{2}-2.814\times 10^{-6}\cdot 93.0^{3}+8.938\times 10^{-9}\cdot 93.0^{4}\right)=-4.59.} This
3445-490: The magnitudes of the distant objects. The absolute magnitude M can also be written in terms of the apparent magnitude m and stellar parallax p : M = m + 5 ( log 10 p + 1 ) , {\displaystyle M=m+5\left(\log _{10}p+1\right),} or using apparent magnitude m and distance modulus μ : M = m − μ . {\displaystyle M=m-\mu .} Rigel has
3510-410: The most luminous persistent objects in the observable universe, although these objects can vary in brightness over astronomically short timescales. At the extreme end, the optical afterglow of the gamma ray burst GRB 080319B reached, according to one paper, an absolute r magnitude brighter than −38 for a few tens of seconds. The Greek astronomer Hipparchus established a numerical scale to describe
3575-410: The object is near opposition. It is known accurately only for a small number of asteroids, hence for most asteroids a value of G = 0.15 {\displaystyle G=0.15} is assumed. In rare cases, G {\displaystyle G} can be negative. An example is 101955 Bennu , with G = − 0.08 {\displaystyle G=-0.08} . In 2012,
3640-534: The phase angle in degrees , then q ( α ) = 2 3 ( ( 1 − α 180 ∘ ) cos α + 1 π sin α ) . {\displaystyle q(\alpha )={\frac {2}{3}}\left(\left(1-{\frac {\alpha }{180^{\circ }}}\right)\cos {\alpha }+{\frac {1}{\pi }}\sin {\alpha }\right).} A full-phase diffuse sphere reflects two-thirds as much light as
3705-500: The properties of the reflecting surface, in particular on its roughness . In practice, different approximations are used based on the known or assumed properties of the surface. The surfaces of terrestrial planets are generally more difficult to model than those of gaseous planets, the latter of which have smoother visible surfaces. Planetary bodies can be approximated reasonably well as ideal diffuse reflecting spheres . Let α {\displaystyle \alpha } be
3770-432: The rotation period nor the axial tilt are known, limiting the predictability. The models presented here do not capture those effects. The brightness of comets is given separately as total magnitude ( m 1 {\displaystyle m_{1}} , the brightness integrated over the entire visible extend of the coma ) and nuclear magnitude ( m 2 {\displaystyle m_{2}} ,
3835-448: The same term This disambiguation page lists articles associated with the same title formed as a letter–number combination. If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=GA6&oldid=1058385811 " Category : Letter–number combination disambiguation pages Hidden categories: Short description
3900-547: The scale from the variable Sun. However, on this SI power scale, the nominal solar luminosity corresponds closely to M bol = 4.74 , a value that was commonly adopted by astronomers before the 2015 IAU resolution. The luminosity of the star in watts can be calculated as a function of its absolute bolometric magnitude M bol as: L ⋆ = L 0 10 − 0.4 M b o l {\displaystyle L_{\star }=L_{0}10^{-0.4M_{\mathrm {bol} }}} using
3965-431: The smaller the numerical value of its absolute magnitude. A difference of 5 magnitudes between the absolute magnitudes of two objects corresponds to a ratio of 100 in their luminosities, and a difference of n magnitudes in absolute magnitude corresponds to a luminosity ratio of 100 . For example, a star of absolute magnitude M V = 3.0 would be 100 times as luminous as a star of absolute magnitude M V = 8.0 as measured in
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#17328871672654030-515: The standard 10 parsecs distance. Consequently, the absolute magnitude of any object equals the apparent magnitude it would have if it were 10 parsecs away. Some stars visible to the naked eye have such a low absolute magnitude that they would appear bright enough to outshine the planets and cast shadows if they were at 10 parsecs from the Earth. Examples include Rigel (−7.8), Deneb (−8.4), Naos (−6.2), and Betelgeuse (−5.8). For comparison, Sirius has an absolute magnitude of only 1.4, which
4095-436: The total and nuclear apparent magnitudes of the comet, respectively, M 1 , 2 {\displaystyle M_{1,2}} are its "absolute" total and nuclear magnitudes, d B S {\displaystyle d_{BS}} and d B O {\displaystyle d_{BO}} are the body-sun and body-observer distances, d 0 {\displaystyle d_{0}}
4160-463: The variables as defined previously. For planets and asteroids , a definition of absolute magnitude that is more meaningful for non-stellar objects is used. The absolute magnitude, commonly called H {\displaystyle H} , is defined as the apparent magnitude that the object would have if it were one astronomical unit (AU) from both the Sun and the observer, and in conditions of ideal solar opposition (an arrangement that
4225-444: Was estimated as M 1 = 8.5 {\displaystyle M_{1}=8.5} . It was subsequently lost and was only rediscovered in 2003. At that time, its absolute magnitude had decreased to M 1 = 22.9 {\displaystyle M_{1}=22.9} , and it was realised that the 1819 apparition coincided with an outburst. 289P/Blanpain reached naked eye brightness (5–8 mag) in 1819, even though it
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