Old instruments
Local Hour Angle
Direct answer
Local Hour Angle is the angular distance measured westward from the observer's meridian to the hour circle of a celestial body.
Local Hour Angle is a local westward celestial angle used in historical astronomy, timekeeping, or navigation.
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At a glance
- Found in
- Historical Almanacs & Instruments
- Related
- Celestial Position Fix, Running Fix, Greenwich Hour Angle, Assumed Position
Local Hour Angle is a local westward celestial angle used in historical astronomy, timekeeping, or navigation.
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The story behind Local Hour Angle
Hour-angle notation became central to practical astronomical and navigation tables.
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The Book of the Sky
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Why Local Hour Angle matters
Local Hour Angle matters because it relates the body's direction to the observer's longitude for altitude and azimuth calculations.
Local Hour Angle in practice: an example
Adding west longitude to Greenwich hour angle and reducing within 360 degrees yields local hour angle under the stated convention.
Where readings of Local Hour Angle go wrong
East and west sign conventions vary across formulas; never memorize an operation without its definition.
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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More in Historical Almanacs & Instruments
- Meridian Table
- Pelorus
- Right Ascension Table
- Sundial
- Almanac Ephemeris
- Astronomical Table
- Computus
- Filar Micrometer
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Common questions
What is local hour angle?
Local Hour Angle is the angular distance measured westward from the observer's meridian to the hour circle of a celestial body.
What do people get wrong about local hour angle?
East and west sign conventions vary across formulas; never memorize an operation without its definition.
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