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.
The magnitude scale is delightfully backwards - the brightest objects have the most negative numbers! Venus can reach magnitude -4.7, while the faintest stars visible to the naked eye are magnitude +6.5, meaning Venus appears about 16,000 times brighter than the dimmest visible stars.
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