Old instruments
Filar Micrometer
Direct answer
Filar Micrometer is a focal-plane device with fine wires moved by a precision screw to measure separation or position angle.
Filar Micrometer is a movable-wire telescope micrometer used in historical astronomy, timekeeping, or navigation.
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At a glance
- Found in
- Historical Almanacs & Instruments
- Related
- Heliometer, Micrometer Eyepiece, Repeating Circle, Artificial Horizon
Filar Micrometer is a movable-wire telescope micrometer 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 Filar Micrometer
Filar micrometers were classic tools for visual double-star and planetary-diameter observation.
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Why Filar Micrometer matters
Filar Micrometer matters because the screw converts a tiny image displacement into a repeatable numerical reading.
Filar Micrometer in practice: an example
The observer places one wire on each star component and converts screw turns into angular separation.
Where readings of Filar Micrometer go wrong
Backlash, illumination, seeing, wire thickness, and subjective contact can bias a single reading.
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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Common questions
What is a filar micrometer?
Filar Micrometer is a focal-plane device with fine wires moved by a precision screw to measure separation or position angle.
What do people get wrong about a filar micrometer?
Backlash, illumination, seeing, wire thickness, and subjective contact can bias a single reading.
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