What is Magnitude (astronomy)?
[[File:Position Alpha Cma.png|thumb|right|250px|{{Center|Sirius. in the [[constellation]], [[Canis Major]], is the brightest star in the night sky (apparent magnitude -1.42). }}]] The '''magnitude''' of a star or other [[celestial object]] is a number that measures its [[Luminosity|brightness]]. '''Apparent magnitude''' ('''{{mvar|m}}''') of a [[celestial object]] is a number that measures its [[brightness]] as seen by an observer on Earth, and '''absolute magnitude''' is its actual brightness adjusted for [[distance]]. The brighter an object appears, the lower its magnitude value. The Sun, at apparent magnitude of −27, is the brightest object in the sky. Magnitude is a [[logarithm]]ic measure. It is measured in a specific [[wavelength]] or [[passband]], usually in [[light|optical]] or [[infrared|near-infrared]] wavelengths. A full moon is −13 magnitude and the brightest planet, [[Venus]], measures −5. The brightest [[man-made]] objects, [[Satellite flare|Iridium flares]], are ranked at −9 and the [[International Space Station]] measures −6.<ref>ISS - Satellite Information. [http://www.heavens-above.com/satinfo.aspx?SatID=25544]</ref> == History == The Greek astronomer [[Hipparchus]] first invented our system of apparent magnitude.<ref name=Belkora19.20>Leila Belkora, ''Minding the Heavens: The Story of our Discovery of the Milky Way'' (Bristol: Institute of Physics, 2003), pp. 19–20</ref> He gave the brightest stars a magnitude of 1 and increased the numbers for dimmer stars.<ref name=Belkora19.20/> About 300 years later [[Ptolemy]] of [[Alexandria]] made an [[encyclopedia]] of stars based on Hipparchus' work.<ref name=Belkora19.20/> The [[Persian people|Persian]] [[astronomer]] [[Al-Sufi]] took Ptolemy's work and gave [[Arabic language|Arabic]] names to the stars some 800 years later.<ref name=Belkora19.20/> Medieval [[Europe]]an astronomers simply [[Translation|translated]] Al-Sufi's work into [[Latin]] which is why many stars today have Arabic names.<ref name=Belkora19.20/> In recent centuries astrono