longitude

Imagine Earth covered in invisible lines running from the North Pole to the South Pole - those are lines of longitude. They help us show how far east or west a place is. Unlike latitude, which starts at the Equator, longitude uses an agreed starting line called the Prime Meridian, which passes through Greenwich, England. Think of it this way: if you told someone to meet you at 40 degrees North latitude, they would know roughly where you were, but you would also need to give 74 degrees West to point to the exact place in New York City. Longitude is measured in degrees, minutes, and seconds.

Longitude is a geographic coordinate that tells us the east-west position of a point on Earth's surface. It is one half of the coordinate system used to locate any place on our planet, with latitude being the other half. While latitude tells you how far north or south a place is from the Equator, longitude tells you how far east or west it is from a reference line called the Prime Meridian.

Historically, finding longitude was a huge challenge for sailors and explorers. Latitude could be worked out by observing the sun or stars, but measuring longitude accurately required very precise timekeeping - something that was not possible until accurate marine chronometers were developed in the 18th century. Before that, ships often got lost or ran aground because they could not judge their east-west position well enough.

The Prime Meridian was agreed on internationally in 1884 and is conventionally placed at Greenwich, England (0° longitude). Longitude is measured in degrees from 0° at the Prime Meridian to 180° east or 180° west. The International Date Line roughly follows the 180° meridian.

So, while latitude gives part of the picture by showing how far north or south something is, longitude completes the map by showing how far east or west it lies. That makes it essential for navigation, mapping, and understanding where places are on Earth. Without it, finding your way around the world would be much harder.