Limiting magnitude is the faintest star a telescope can reveal to the eye under good dark skies, and it climbs steadily with aperture because a bigger opening gathers more light. A common estimate adds five times the base ten logarithm of the aperture in millimeters to a baseline near two, so a small refractor might reach magnitude eleven while a large dobsonian pushes past fourteen. This calculator gives that visual limit from your aperture and lets you nudge a sky quality allowance for light polluted or pristine sites. Use it to judge whether a faint galaxy or comet is realistically within reach before you set up. All calculation runs in your browser with nothing uploaded.
Limiting magnitude is the faintest star a telescope can reveal to the eye under good dark skies, and it climbs steadily with aperture because a bigger opening gathers more light. A common estimate adds five times the base ten logarithm of the aperture in millimeters to a baseline near two, so a small refractor might reach magnitude eleven while a large dobsonian pushes past fourteen.
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