Definition:Meridian (Terrestrial)

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A (terrestrial) meridian is a semi-great circle on Earth's surface whose endpoints are Earth's poles.


Principal Meridian

The principal meridian is the meridian of Earth which passes through the Royal Observatory in Greenwich, Greater London, England, which is used as the internationally-recognised $0 \degrees$ reference longitude meridian.

Also defined as

Some sources recognise a (terrestrial) meridian to be a complete great circle passing through both of Earth's poles.

However, this definition is less convenient.

Also known as

In common parlance, a terrestrial meridian is usually referred to as just a meridian.

The terrestrial descriptor is added so as to distinguish it from a celestial meridian.

Also see