Old instruments
Astronomical Quadrant
Direct answer
Astronomical Quadrant: An Astronomical Quadrant is a quarter-circle instrument whose graduated arc is used to measure altitude or perform time and coordinate calculations.
An Astronomical Quadrant uses a graduated quarter circle to measure or calculate sky angles.
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At a glance
- Found in
- Historical Almanacs & Instruments
- Related
- Almanac, Astronomical Almanac, Nautical Almanac, Astrolabe
An Astronomical Quadrant uses a graduated quarter circle to measure or calculate sky angles.
An engraved functional orientation; the page explains the real instrument, method, or publication.
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The story behind Astronomical Quadrant
Quadrants were made in many sizes and traditions, from hand-held mathematical instruments to monumental arcs fixed in observatories.
A one-minute story
The Book of the Sky
How people learned to read the sky, from Babylon to the day you were born.
Why Astronomical Quadrant matters
The simple ninety-degree geometry supported portable time finding as well as large observatory instruments for precise positional measurement.
Astronomical Quadrant in practice: an example
A horary quadrant can combine a measured solar altitude with engraved calendar lines to estimate local apparent time.
Where readings of Astronomical Quadrant go wrong
It is a mistake to infer modern precision from a photograph; alignment, plumb, scale divisions, refraction, and the maker's intended latitude all affect use.
Sources and editorial method
Research references used for this entry include:
- Royal Museums Greenwich: Horary Quadrant - Museum documentation of a quadrant used to measure solar altitude and find time.
- Royal Museums Greenwich: Astronomical and Navigational Instruments - Museum reference collection for astrolabes, armillary spheres, quadrants, nocturnals, sundials, and navigation instruments.
- Source
- The Great Almanac Dictionary
- Category
- Historical Almanacs & Instruments
- Last updated
- 2026-09-26
Measure an altitude on a quadrant
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Common questions
What is an Astronomical Quadrant?
An Astronomical Quadrant is a quarter-circle instrument whose graduated arc is used to measure altitude or perform time and coordinate calculations.
What do people get wrong about an Astronomical Quadrant?
It is a mistake to infer modern precision from a photograph; alignment, plumb, scale divisions, refraction, and the maker's intended latitude all affect use.
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