The faintest magnitude of stars visible under given observing conditions, whether with the naked eye, binoculars, or a telescope. Limiting magnitude indicates the quality of viewing conditions and instrument performance.
Combining 'limiting' from Latin 'limes' (boundary) and 'magnitude' from Latin 'magnitudo' (greatness). The concept developed in the 19th century as astronomers standardized brightness measurements and characterized observing capabilities.
Your eye is an amazingly sensitive detector! Under perfect dark skies, the naked-eye limiting magnitude reaches about 6.5, meaning you can see stars 100 times fainter than the brightest ones - that's detecting just a few hundred photons per second hitting your retina.
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