Definition
The angular distance, measured in degrees east or west, of a point on the Earth's surface from the Prime Meridian (0°), which runs through Greenwich, England. Lines of longitude (meridians) run from the North Pole to the South Pole and range from 0° to 180° east or west.
Plain English
How far east or west a place is on the Earth, measured in degrees from the line that runs through Greenwich, England.
Context Anchor
Pilots see longitude in coordinates on charts, GPS displays, flight planning tools, airport information, and some NOTAMs.
Derivation
From the Latin longitudo, meaning 'length.' Early mapmakers thought of the Earth as longer east-to-west than north-to-south, so the east-west measurement became the 'length' coordinate. That is why longitude lines measure east-west position even though the lines themselves run north-south.
Why Pilots Care
Critical for accurate navigation and determining exact geographic position during flight planning and en route operations.
Analogy
Think of longitude as one part of an address for a point on Earth. It does not name the place by itself, but it helps pin down exactly where that place is.
Intuition Check
LONG does not mean “a long distance” here. It means longitude: the east-west part of a geographic position.
Example Sentence 1
The pilot entered the airport's latitude and longitude into the GPS before departure.
Example Sentence 2
Check the sectional chart for the airport's exact LONG and latitude coordinates.