Sky science
Local Meridian
Direct answer
Local Meridian: The Local Meridian is the north-south celestial great circle defined for one observer’s longitude.
It is the observer-specific meridian of the sky.
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At a glance
- Found in
- Astronomy & Skywatching
- Related
- Declination Circle, Celestial Meridian, Hour Angle, Position Angle
It is the observer-specific meridian of the sky.
A scientific orientation to scale, light, or motion; the article supplies the precise definition.
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The story behind Local Meridian
Local meridians underpinned apparent solar time before standardized time zones.
A one-minute story
The Wandering Stars
How the moving planets were watched, named and found, and what a transit is.
Why Local Meridian matters
Local Meridian determines local culmination and connects longitude with astronomical time.
How to read Local Meridian
Do not reuse meridian times calculated for another longitude.
Local Meridian in practice: an example
Local solar noon occurs when the Sun crosses the observer’s meridian.
Where readings of Local Meridian go wrong
Clock noon and local meridian transit usually do not coincide exactly.
Sources and editorial method
Research references used for this entry include:
- U.S. Naval Observatory: Astronomical Almanac Glossary - Definitions for astronomical coordinates, time, reference systems, and observable phenomena.
- U.S. Naval Observatory: Astronomical Data - Authoritative services for celestial positions, rise and set events, phases, and related calculations.
- Source
- The Great Almanac Dictionary
- Category
- Astronomy & Skywatching
- Last updated
- 2026-09-26
Find your sky’s north-south line
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Common questions
What is the Local Meridian?
The Local Meridian is the north-south celestial great circle defined for one observer’s longitude.
What do people get wrong about the Local Meridian?
Clock noon and local meridian transit usually do not coincide exactly.
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