What does longitude mean?
Longitude is the geographical coordinate that describes a location’s position east or west of the prime meridian, the imaginary line passing through Greenwich, England. It is measured in degrees, minutes, and seconds, allowing positions on Earth to be specified precisely for navigation, mapping, and scientific work. Longitude is most often discussed alongside latitude, which indicates a position north or south of the equator. Together, the two coordinates form the familiar grid that appears on maps and globes. The word also has a specialized astronomical use for an angular position measured along the celestial sphere. Although locations near the prime meridian have longitude close to zero, the coordinate grows in either an easterly or westerly direction until it reaches 180 degrees. Longitude is therefore essential whenever a precise, shared system is needed to describe where something lies on Earth or in the sky.
nounThe angular distance of a point on Earth’s surface, measured in degrees east or west of the prime meridian. In astronomy, longitude is the analogous angular coordinate measured along a celestial circle from a reference point.
- The angular distance of a geographical position east or west of the prime meridian.
- In astronomy, an angular coordinate measured eastward along the celestial equator from the vernal equinox.
"The ship’s longitude changed as it sailed steadily westward across the Atlantic."
"Maps use lines of latitude and longitude to identify positions across the globe."
"The observatory recorded the star’s changing longitude as it moved across the celestial sphere."
Used when referring to multiple east–west angular coordinates or locations specified by longitude.
"The atlas lists the longitudes of the participating observatories."
Without longitude, every place on Earth would still have an address—but you could not say how far east or west it lay.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of longitude
English longitude comes from Latin longitudo, a noun meaning “length” or “extent,” derived from longus, meaning “long.” The geographical sense developed from the early modern period as explorers and navigators sought a systematic way to describe east–west position. Related English forms such as longitudinal and longitudinally preserve the same Latin root through its adjective and adverb derivatives.
Related word forms
How longitude is actually used
Longitude is primarily formal and technical, especially in geography, navigation, cartography, and astronomy. In everyday descriptions of a place, people may speak informally of its east–west position, but longitude specifically refers to the angular coordinate measured from the prime meridian.
Easily confused with longitude
Longitude measures position east or west of the prime meridian, while latitude measures position north or south of the equator.