Sky science
Limiting Magnitude
Direct answer
Limiting Magnitude is the faintest apparent magnitude detectable under stated observer, instrument, and sky conditions.
It is a practical faintness threshold.
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At a glance
- Found in
- Astronomy & Skywatching
- Related
- Airglow, Dark Adaptation, Naked-Eye Astronomy, Binocular Astronomy
It is a practical faintness threshold.
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The story behind Limiting Magnitude
Star counts and calibrated sequences made limiting magnitude a repeatable observing metric.
A one-minute story
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Why Limiting Magnitude matters
Limiting Magnitude summarizes how darkness, aperture, experience, and target altitude affect detection.
How to read Limiting Magnitude
Report the method and conditions rather than one universal limit.
Limiting Magnitude in practice: an example
A dark adapted observer may see fainter stars at a rural site than in a city.
Where readings of Limiting Magnitude go wrong
Point-source limits do not directly predict extended-object visibility.
Sources and editorial method
Research references used for this entry include:
- NASA Science: Skywatching FAQ - NASA guidance for observing stars, planets, constellations, and changing sky events.
- European Southern Observatory: Technology for Telescopes - Observatory reference for aperture, angular resolution, atmospheric seeing, mirrors, and telescope technology.
- Source
- The Great Almanac Dictionary
- Category
- Astronomy & Skywatching
- Last updated
- 2026-09-26
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Common questions
What is limiting magnitude?
Limiting Magnitude is the faintest apparent magnitude detectable under stated observer, instrument, and sky conditions.
What do people get wrong about limiting magnitude?
Point-source limits do not directly predict extended-object visibility.
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