Old instruments
Nautical Almanac
Direct answer
Nautical Almanac: The Nautical Almanac is an annual publication of tabulated celestial-position data arranged for practical navigation at sea and other forms of celestial navigation.
The Nautical Almanac supplies yearly celestial data for navigational sight reduction.
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At a glance
- Found in
- Historical Almanacs & Instruments
- Related
- Almanac, Astronomical Almanac, Astrolabe, Armillary Sphere
The Nautical Almanac supplies yearly celestial data for navigational sight reduction.
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Your daily Almanac letter
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The story behind Nautical Almanac
Nautical almanacs became essential companions to improved marine timekeeping and mathematical navigation, giving mariners standardized predictions of celestial positions.
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The Book of the Sky
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Why Nautical Almanac matters
Nautical Almanac connects a measured angle between a celestial body and the horizon with the time-dependent reference data needed to determine a line of position.
Nautical Almanac in practice: an example
A navigator combines a timed sextant altitude of the Sun with the almanac's data and correction tables to calculate a position line.
Where readings of Nautical Almanac go wrong
The usual misreading is to treat the tables alone as a complete navigation system or omit instrument, horizon, refraction, and height corrections.
Sources and editorial method
Research references used for this entry include:
- U.S. Naval Observatory: Astronomical and Navigational Almanacs - Official description of current Astronomical Almanac and Nautical Almanac publications.
- U.S. Naval Observatory: Astronomical Almanac Glossary - Reference definitions for astronomical coordinates, events, calendars, and time scales.
- Source
- The Great Almanac Dictionary
- Category
- Historical Almanacs & Instruments
- Last updated
- 2026-09-26
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Common questions
What is the Nautical Almanac?
The Nautical Almanac is an annual publication of tabulated celestial-position data arranged for practical navigation at sea and other forms of celestial navigation.
What do people get wrong about the Nautical Almanac?
The usual misreading is to treat the tables alone as a complete navigation system or omit instrument, horizon, refraction, and height corrections.
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One short letter at 7 each morning: the day’s theme read for your own chart, and one thing to do with it.
