Old instruments
Altitude Correction
Direct answer
Altitude Correction is the adjustments applied to an instrument altitude so it represents the required celestial-center geometry.
Altitude Correction is a celestial-angle correction set used in historical astronomy, timekeeping, or navigation.
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At a glance
- Found in
- Historical Almanacs & Instruments
- Related
- Observed Altitude, Computed Altitude, Dip Correction, Refraction Correction
Altitude Correction is a celestial-angle correction set used in historical astronomy, timekeeping, or navigation.
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The story behind Altitude Correction
Published correction tables standardized reductions that had once required lengthy separate calculations.
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Why Altitude Correction matters
Altitude Correction matters because instrument height, atmosphere, body size, parallax, and instrument error separate a raw angle from a reducible one.
Altitude Correction in practice: an example
A lower-limb Sun sight may receive index, dip, refraction, parallax, and semidiameter treatment.
Where readings of Altitude Correction go wrong
Combining tabular corrections with separate duplicate corrections can count the same effect twice.
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
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Common questions
What is Altitude Correction?
Altitude Correction is the adjustments applied to an instrument altitude so it represents the required celestial-center geometry.
What do people get wrong about Altitude Correction?
Combining tabular corrections with separate duplicate corrections can count the same effect twice.
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