Old instruments
Planisphere
Direct answer
Planisphere is a circular star chart whose movable mask shows the stars expected above the horizon for a chosen date and time.
Planisphere is a rotating sky map used in historical astronomy, timekeeping, or navigation.
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At a glance
- Found in
- Historical Almanacs & Instruments
- Related
- Lunar Distance Table, Star Atlas, Volvelle, Calendar Wheel
Planisphere is a rotating sky map 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 Planisphere
Portable planispheres popularized older rotating-chart principles as simple educational sky guides.
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 Planisphere matters
Planisphere matters because it teaches the seasonal rotation of the visible sky without needing power or a live connection.
How to read Planisphere
Planisphere by selecting a model speaks to the observer's latitude and aligning local date and time with the correct daylight-saving adjustment.
Planisphere in practice: an example
Setting a northern planisphere to 10 p.m. on an October date reveals which constellations should be above the local horizon.
Where readings of Planisphere go wrong
A planisphere is approximate near its latitude limits and does not predict clouds, planets, or exact horizon obstructions.
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.
- U.S. Naval Observatory: Astronomical Applications Data Services - Authoritative services for positions, rise and set data, phases, seasons, eclipses, and astronomical dates.
- 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 planisphere?
Planisphere is a circular star chart whose movable mask shows the stars expected above the horizon for a chosen date and time.
What do people get wrong about a planisphere?
A planisphere is approximate near its latitude limits and does not predict clouds, planets, or exact horizon obstructions.
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