méridien

A méridien refers to an imaginary line on the Earth's surface that runs from the North Pole to the South Pole, connecting points of equal longitude. These lines are part of a global grid system used in geography, navigation, and cartography to determine precise locations on the planet. The term originates from the Latin word *meridies*, meaning "midday," as the sun crosses the meridian at its highest point in the sky at local noon.

Meridians are measured in degrees east and west of the Prime Meridian, which is designated as 0° longitude and passes through the Royal Observatory in Greenwich, England. This reference line divides the Earth into Eastern and Western Hemispheres. Each degree of longitude is further subdivided into 60 minutes, and each minute into 60 seconds, allowing for highly detailed location specifications.

Meridians play a crucial role in timekeeping, as they help define time zones. Locations on the same meridian share the same local solar time, though adjustments are made for standard time zones to accommodate regional needs. The concept of meridians is fundamental in astronomy, where they are used to track celestial objects' positions relative to the Earth's rotation.

In navigation, meridians assist in determining longitude, which, along with latitude (measured by parallels), provides a coordinate system for pinpointing locations. Historically, accurately calculating longitude was a significant challenge, leading to advancements in navigation technology, such as marine chronometers.

Today, meridians remain essential in global positioning systems (GPS) and digital mapping, ensuring accurate spatial data for applications ranging from travel to scientific research. The system of meridians and parallels forms the basis of modern cartography, enabling precise representation of the Earth's surface.