Old instruments
Alidade
Direct answer
Alidade is a rotating sighting rule or telescope used to define a direction on a graduated instrument.
Alidade is a sighting rule used in historical astronomy, timekeeping, or navigation.
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At a glance
- Found in
- Historical Almanacs & Instruments
- Related
- Sector Instrument, Dioptra, Plumb Line, Gnomon
Alidade is a sighting rule 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 Alidade
Alidades appear on astrolabes, plane tables, quadrants, surveying instruments, and later telescopic circles.
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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 Alidade matters
Alidade matters because it converts a line of sight into a readable angle or plotted bearing.
Alidade in practice: an example
On an astrolabe, the alidade can sight a star while its pointer marks altitude on the limb.
Where readings of Alidade go wrong
A bent sight, parallax, poor leveling, or a shifted pivot introduces systematic error.
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
Explore Alidade
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More in Historical Almanacs & Instruments
- Astronomical Ephemeris Table
- Clepsydra
- Equatorial Telescope
- Latitude by Meridian Altitude
- Mariner's Astrolabe
- Octant
- Regulator Clock
- Star Sight
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Common questions
What is an alidade?
Alidade is a rotating sighting rule or telescope used to define a direction on a graduated instrument.
What do people get wrong about an alidade?
A bent sight, parallax, poor leveling, or a shifted pivot introduces systematic error.
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