Where is longitude measured from

Because of the Earth's curvature , the actual distance of a degrees, minutes, and seconds of longitude depends on its distance from the Equator. The greater the distance, the shorter the length between meridians. All meridians meet at the North and South Poles. Longitude is related to latitude , the measurement of distance north or south of the Equator.

Lines of latitude are called parallel s. Maps are often marked with parallels and meridians, creating a grid. The point in the grid where parallels and meridians intersect is called a coordinate. Coordinates can be used to locate any point on Earth. Knowing the exact coordinates of a site degrees, minutes, and seconds of longitude and latitude is valuable for military , engineering , and rescue operation s.

Coordinates can give military leaders the location of weapons or enemy troops. Coordinates help engineers plan the best spot for a building, bridge, well, or other structure.

Coordinates help airplane pilots land planes or drop aid packages in specific locations. Into the Great Wide Open It was not until the 18th century that people were able to correctly determine their longitude, even though they had been able to figure out latitude for some time.

Not being able to reckon longitude was dangerous for sailors. Without an exact location, they could easily run out of food or water on a long expedition into uncharted territory.

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The Rights Holder for media is the person or group credited. All rights reserved. Credit: Illinois State University. Try it! The Mystery Class Challenge. Mystery Class is a global game of hide-and-seek. Students track seasonal changes in sunlight to find ten secret sites around the world.

Pocket watches were in their infancy in the 17th century but until the balance spring was added to the balance wheel of pocket watches in the midth century, the pendulum clock was the most advanced timekeeper of the age. The motion of a ship was the main issue preventing a pendulum clock in the 18th century from keeping time at sea.

A pendulum would not swing consistently to keep time while a ship was pitching and yawing on the open seas. John Harrison was the first inventor to work towards a viable solution to this problem. His first sea clock, H1, did not have a pendulum but two interconnected bar balances which counteracted each other, ensuring that the mechanism lost less time. H1 was a significant step towards accurately determining longitude at sea. His next design, H4, was the culmination of more than 30 years of research to create an accurate marine timekeeper.

Harrison took a dramatic design change for H4 after realising that the pocket watch offered the solution to timekeeping at sea — the compact body and robust balance mechanisms of pocket watches offered the stability a marine timekeeper needed. The most common system for locating points on the earth is with "Longitudes" and "Latitudes". Both longitude and latitude are angles measured with the center of the earth as an origin. A longitude is an angle from the prime merdian, measured to the east longitudes to the west are negative.

Latitudes measure an angle up from the equator latitudes to the south are negative. Figure 1.