Old instruments
Refraction Correction
Direct answer
Refraction Correction is the adjustment for Earth's atmosphere bending a celestial ray and raising the body's apparent altitude.
Refraction Correction is an atmospheric bending correction used in historical astronomy, timekeeping, or navigation.
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At a glance
- Found in
- Historical Almanacs & Instruments
- Related
- Altitude Correction, Dip Correction, Semidiameter Correction, Almanac
Refraction Correction is an atmospheric bending correction used in historical astronomy, timekeeping, or navigation.
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The story behind Refraction Correction
Astronomers and navigators developed refraction tables as increasingly precise observations exposed systematic bending.
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Why Refraction Correction matters
Refraction Correction matters because refraction is strongest near the horizon and separates apparent direction from the vacuum geometric direction.
Refraction Correction in practice: an example
A low star sight receives a larger refraction correction than a high-altitude sight.
Where readings of Refraction Correction go wrong
Near-horizon refraction is variable and can be anomalous, so a standard table cannot remove every local effect.
Sources and editorial method
Research references used for this entry include:
- National Geospatial-Intelligence Agency: The American Practical Navigator - Official modern reference for navigation principles, celestial observations, sight reduction, and navigational tables.
- U.S. Naval Observatory: Astronomical and Navigational Almanacs - Official descriptions of the Astronomical Almanac, Nautical Almanac, and their tabular data.
- Source
- The Great Almanac Dictionary
- Category
- Historical Almanacs & Instruments
- Last updated
- 2026-09-26
Explore Refraction Correction
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Common questions
What is refraction correction?
Refraction Correction is the adjustment for Earth's atmosphere bending a celestial ray and raising the body's apparent altitude.
What do people get wrong about refraction correction?
Near-horizon refraction is variable and can be anomalous, so a standard table cannot remove every local effect.
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