A measure of how bright a star or other celestial object appears from Earth, regardless of distance. The scale is logarithmic and inverted, with brighter objects having smaller or negative values.
From Latin 'apparere' (to appear) and 'magnitudo' (greatness). The magnitude system originated with ancient Greek astronomer Hipparchus around 150 BCE, who classified stars into six brightness categories, later mathematically formalized in the 19th century.
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