Old instruments
Meridian Circle
Direct answer
Meridian Circle is a telescope constrained to the meridian and combined with graduated circles for measuring star positions.
Meridian Circle is a precision transit-and-altitude telescope used in historical astronomy, timekeeping, or navigation.
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At a glance
- Found in
- Historical Almanacs & Instruments
- Related
- Plumb Line, Gnomon, Transit Instrument, Mural Quadrant
Meridian Circle is a precision transit-and-altitude telescope 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 Meridian Circle
Meridian circles became foundational nineteenth- and twentieth-century instruments for positional astronomy.
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The Book of the Sky
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Why Meridian Circle matters
Meridian Circle matters because timing transit and measuring zenith distance together supported precise catalogues and observatory reference frames.
How to read Meridian Circle
Meridian Circle by calibrating level, collimation, circle division, refraction, and clock corrections speaks to a meridian observation.
Meridian Circle in practice: an example
A star's transit time yields right ascension while the circle reading helps determine declination.
Where readings of Meridian Circle go wrong
Flexure, refraction, pivot error, and catalogue-clock assumptions must be reduced before publishing a position.
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.
- Royal Museums Greenwich: A Unique History of Timekeeping - Museum overview of marine chronometers, astronomical regulators, and the development of precision timekeeping.
- Source
- The Great Almanac Dictionary
- Category
- Historical Almanacs & Instruments
- Last updated
- 2026-09-26
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More in Historical Almanacs & Instruments
- Orrery
- Regulator Clock
- Sun Sight
- Astronomical Quadrant
- Compass Rose
- Equinoctial Ring Dial
- Line of Position
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Common questions
What is a meridian circle?
Meridian Circle is a telescope constrained to the meridian and combined with graduated circles for measuring star positions.
What do people get wrong about a meridian circle?
Flexure, refraction, pivot error, and catalogue-clock assumptions must be reduced before publishing a position.
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