Old instruments
Observed Altitude
Direct answer
Observed Altitude is the celestial angle read from the sextant or other instrument before the full correction sequence.
Observed Altitude is a raw instrument altitude used in historical astronomy, timekeeping, or navigation.
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At a glance
- Found in
- Historical Almanacs & Instruments
- Related
- Greenwich Hour Angle, Assumed Position, Computed Altitude, Altitude Correction
Observed Altitude is a raw instrument altitude used in historical astronomy, timekeeping, or navigation.
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The story behind Observed Altitude
Navigation workbooks traditionally separated sextant altitude, corrected intermediate values, and final observed altitude notation.
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Why Observed Altitude matters
Observed Altitude matters because keeping the raw observation distinct preserves an audit trail from instrument reading to final altitude.
Observed Altitude in practice: an example
A sextant reading of 28 degrees 14.6 minutes is logged before dip and body corrections are applied.
Where readings of Observed Altitude go wrong
Terminology varies by manual, so verify whether a worksheet uses observed altitude before or after index and dip correction.
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.
- Source
- The Great Almanac Dictionary
- Category
- Historical Almanacs & Instruments
- Last updated
- 2026-09-26
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More in Historical Almanacs & Instruments
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Common questions
What is observed altitude?
Observed Altitude is the celestial angle read from the sextant or other instrument before the full correction sequence.
What do people get wrong about observed altitude?
Terminology varies by manual, so verify whether a worksheet uses observed altitude before or after index and dip correction.
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