Old instruments
Backstaff
Direct answer
Backstaff is an angular instrument that lets an observer measure solar altitude while facing away from the Sun.
Backstaff is a shadow-based navigation instrument used in historical astronomy, timekeeping, or navigation.
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At a glance
- Found in
- Historical Almanacs & Instruments
- Related
- Right Ascension Table, Cross Staff, Davis Quadrant, Octant
Backstaff is a shadow-based navigation instrument used in historical astronomy, timekeeping, or navigation.
An engraved functional orientation; the page explains the real instrument, method, or publication.
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The story behind Backstaff
The Davis-style backstaff became a major seventeenth-century marine instrument before the octant and sextant.
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The Book of the Sky
How people learned to read the sky, from Babylon to the day you were born.
Why Backstaff matters
Backstaff matters because its shadow geometry reduced the need to stare toward intense sunlight during a noon observation.
Backstaff in practice: an example
At local noon, a backstaff altitude could support a latitude calculation.
Where readings of Backstaff go wrong
Facing away from the Sun is safer than direct sighting but does not remove the need for trained handling and eye protection around bright reflections.
Sources and editorial method
Research references used for this entry include:
- Royal Museums Greenwich: Backstaff - Museum documentation of the backstaff, its arcs, vanes, scales, and solar-altitude use.
- Royal Museums Greenwich: Astronomical and Navigational Instruments - Museum reference collection for historical observing, calculating, timekeeping, and navigation instruments.
- 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 a backstaff?
Backstaff is an angular instrument that lets an observer measure solar altitude while facing away from the Sun.
What do people get wrong about a backstaff?
Facing away from the Sun is safer than direct sighting but does not remove the need for trained handling and eye protection around bright reflections.
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