Principles of Celestial Navigation

Basics » Earth Position: Latitude and Longitude

Most people understand that a location on Earth is described by a set of coordinates, the location's longitude and latitude. (Height is often included, but we will ignore it for now). The geographic coordinates are unique. That is, there are no two places on Earth that have the same longitude and latitude.

Our longitude is an angular measure along Earth's equator of how far East or West we are from the prime meridian that goes through Greenwich, England. For example, if we are standing in Greenwich, our longitude is zero. If we are in Warsaw, Poland our longitude is 21 degrees East. Lima, Peru's longitude is 77 degrees West.

Our latitude is an angular measure of how far North or South from the equator we are. For example, if we are exactly on the equator, our latitude is zero. At the North Pole, our latitude is 90 degrees North; at the South Pole, our latitude is 90 degrees South.