Longitude

Longitude is a geographic coordinate that specifies the east-west position of a point on the Earth's surface, or the surface of a celestial body. It is an angular measurement, usually expressed in degrees and denoted by the Greek letter lambda (λ). Meridians (lines running from the North Pole to the South Pole) connect points with the same longitude. The prime meridian, which is 0° longitude, passes through the Royal Observatory, Greenwich, England.

History

The concept of longitude was developed by the ancient Greeks and later refined and globally adopted in the Western world. The measurement of longitude is important both to cartography and for ocean navigation. Mariners and explorers for most of history struggled to determine longitude. Finding a method of determining longitude took centuries, resulting in the history of longitude recording the effort of some of the greatest scientific minds.

Modern usage

Longitude is used together with latitude to specify the precise location of features on the surface of the Earth. Longitude is commonly used in navigation, such as marine navigation where it is paired with latitude. It is also used in global positioning systems (GPS).

Determining longitude

Longitude can be calculated if the precise time of a sighting is known. This method works because the Earth rotates at a steady rate of 360° per day, or 15° per hour.

See also

• Latitude
• Geographic coordinate system
• Prime Meridian
• Royal Observatory, Greenwich

References

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