Old instruments
Reflecting Circle
Direct answer
Reflecting Circle is a circular double-reflection instrument built to measure and repeat angular observations around a complete graduated limb.
Reflecting Circle is a full-circle reflection instrument used in historical astronomy, timekeeping, or navigation.
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At a glance
- Found in
- Historical Almanacs & Instruments
- Related
- Davis Quadrant, Octant, Hadley Quadrant, Mariner's Astrolabe
Reflecting Circle is a full-circle reflection 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 Reflecting Circle
Reflecting circles were developed for astronomy, geodesy, and navigation as precision relatives of the sextant.
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Why Reflecting Circle matters
Reflecting Circle matters because repeated readings around the circle can reveal or average certain graduation and observation errors.
Reflecting Circle in practice: an example
Several repetitions of the same separation can be combined into a refined angular value.
Where readings of Reflecting Circle go wrong
Mechanical strain, eccentricity, collimation, and an incorrect repetition procedure can defeat the expected precision.
Sources and editorial method
Research references used for this entry include:
- 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 reflecting circle?
Reflecting Circle is a circular double-reflection instrument built to measure and repeat angular observations around a complete graduated limb.
What do people get wrong about a reflecting circle?
Mechanical strain, eccentricity, collimation, and an incorrect repetition procedure can defeat the expected precision.
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