Meridian (geography)
A line of longitude connecting points of equal longitude.
A meridian is the locus connecting points of equal longitude, a coordinate line for longitudes. On a spherical Earth model, a meridian is a great semicircle; on an ellipsoid model, it is half of a north-south great ellipse.
- field
- Geography and geodesy
- known_for
- Line of longitude; basis for time zones and navigation
- prime_meridian
- IERS Reference Meridian (current); historically Greenwich
- etymology
- From Latin meridies, meaning 'midday'
Lore & Background
The term meridian comes from the Latin meridies, meaning 'midday'; the subsolar point passes through a given meridian at solar noon. The same Latin stem gives rise to a.m. (ante meridiem) and p.m. (post meridiem). The first prime meridian was set by Eratosthenes in 200 BCE, but had problems due to lack of latitude measurement. By the early modern era, multiple locations were used as prime meridians, with Paris and Greenwich being most often acknowledged.
Reader's Guide
This was influenced by the USA already using Greenwich for its national time zone system and by 72% of world commerce depending on sea-charts using Greenwich. The magnetic meridian is an equivalent line connecting magnetic poles, and the angle between magnetic and true meridian is magnetic declination, important for compass navigation.
Did You Know?
- The term meridian comes from Latin meridies, meaning 'midday'.
Frequently Asked Questions
What is a meridian in geography?
A meridian is a coordinate line that links every point sharing the same longitude value. On a spherical Earth it appears as a great semicircle, while on an ellipsoidal model it becomes half of a north-south great ellipse.
What is the Prime Meridian?
The Prime Meridian is the zero-degree reference line from which all other longitudes are counted east or west. The current official standard is the IERS Reference Meridian, although Greenwich, England held that role for most of modern history.
Why do meridians matter for time zones and navigation?
Meridians underpin the global time-zone system because local solar noon is defined by the sun crossing a particular line of longitude. They also give navigators the longitudinal framework needed to fix an east-west position at sea or on land.
Where does the word 'meridian' come from?
The term derives from the Latin meridies, meaning 'midday.' The name fits naturally because the sun reaches its highest point above the horizon exactly when it crosses a given meridian.
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