Old instruments
Greenwich Hour Angle
Direct answer
Greenwich Hour Angle is the angular distance measured westward from the Greenwich meridian to a body's hour circle.
Greenwich Hour Angle is a Greenwich-referenced celestial angle used in historical astronomy, timekeeping, or navigation.
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At a glance
- Found in
- Historical Almanacs & Instruments
- Related
- Running Fix, Local Hour Angle, Assumed Position, Observed Altitude
Greenwich Hour Angle is a Greenwich-referenced celestial angle used in historical astronomy, timekeeping, or navigation.
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The story behind Greenwich Hour Angle
Greenwich hour angle became a compact standard coordinate in nautical almanacs and sight reduction.
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Why Greenwich Hour Angle matters
Greenwich Hour Angle matters because it supplies the almanac bridge between a body's celestial position and terrestrial longitude.
Greenwich Hour Angle in practice: an example
A navigator looks up the Sun's hourly GHA and adds the minute-and-second increment for the sight time.
Sources and editorial method
Research references used for this entry include:
- U.S. Naval Observatory: Astronomical and Navigational Almanacs - Official descriptions of the Astronomical Almanac, Nautical Almanac, and their tabular data.
- 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 Greenwich Hour Angle?
Greenwich Hour Angle is the angular distance measured westward from the Greenwich meridian to a body's hour circle.
Why does Greenwich Hour Angle matter?
Greenwich Hour Angle matters because it supplies the almanac bridge between a body's celestial position and terrestrial longitude.
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