Longitude
Longitude is the geographic coordinate that specifies the east-west position of a point on the Earth’s surface, measured in degrees(°), minutes(‘) and seconds(“) from the Prime Meridian.
Longitude is one of the two key coordinates used in navigation and mapping to determine a specific location on the Earth’s surface. The other is latitude. While latitude measures how far north or south a point is from the Equator, longitude measures how far east or west a point is from the Prime Meridian, which is the zero-degree line of longitude that passes through Greenwich, England.
Longitude lines, also called meridians, run from the North Pole to the South Pole and are spaced widest at the Equator, converging at the poles. These lines are measured in degrees, minutes, and seconds. Each degree of longitude is subdivided into 60 minutes and each minute into 60 seconds. The Earth is divided into 360 degrees of longitude, 180 degrees to the east and 180 degrees to the west of the Prime Meridian.
The Prime Meridian (0° longitude) is the starting point for measuring longitude, and the opposite side of the Earth, at 180° longitude, is known as the International Date Line. Locations east of the Prime Meridian are designated east longitude (E), and locations to the west are designated west longitude (W).
For example, the coordinates 30°E would indicate a point 30 degrees east of the Prime Meridian, while 45°W would indicate a point 45 degrees west of the Prime Meridian. When combined with latitude, longitude allows mariners to pinpoint their exact location on the globe, which is essential for navigation, especially when out of sight of land.
Historically, determining longitude at sea was a significant challenge for mariners, requiring precise timekeeping. John Harrison’s invention of the marine chronometer in the 18th century revolutionised navigation. It allowed sailors to calculate their longitude accurately by comparing the local time (determined by the position of the sun) with the time at a known reference point, such as Greenwich.
In modern times, GPS (Global Positioning System) technology has made determining longitude (and latitude) much easier and more accurate, but the basic principles of longitude remain the same. Understanding longitude is crucial for navigation, chart plotting, and ensuring safe passage through the world’s oceans.
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