Latitude and Longitude

Knowing latitude and longitude is a simple way to identify location. Navigators talk about their north-south position using parallels of latitude—the lines running across the map, chart, or globe, from left to right, west to east. A latitude coordinate tells how far north or south you are from the equator, the line that goes around the middle of the globe dividing it into the Northern and Southern Hemispheres. A longitude coordinate tells how far east or west you are from the prime meridian, the line of longitude that runs through Greenwich, England. Lines of longitude, which are also called meridians, run north and south on a map and converge at the poles.

Distance is written in terms of degrees. The equator lies at 0 degrees and the parallels of latitude north of the equator are identified as north, and those south of the equator are identified as south. The North Pole lies at latitude 90 degrees north, and the South Pole at 90 degrees south. The prime meridian lies at 0 degrees longitude. Meridians of longitude east of the prime meridian are designated as east, and those west of the prime meridian are identified as west.

Where longitude 180 degrees west meets longitude 180 degrees east in the Pacific Ocean is the International Date Line, the place where the date actually changes. Fortunately the International Date Line doesn’t go through any islands—it zigs and zags along the 180-degree meridian—otherwise for people living on one side of the date line it would be today, and for their neighbors living on the other side it would be tomorrow, which could get very confusing. Without the International Date Line, travelers going westward would discover that when they returned home, they had spent one more day on their vacation than they thought, even though they had kept careful tally of the days. This happened to Magellan’s crew after their first circumnavigation of the globe. Likewise, a person traveling eastward would find that one fewer day had elapsed than he or she had recorded, as happened to Phileas Fogg in Around the World in Eighty Days by Jules Verne.

Each degree of latitude and longitude is divided into 60 minutes, and each minute is further divided into 60 seconds (think of how time is divided and you’ll never forget this). Navigators measure distance in nautical miles. One nautical mile equals one minute of one degree and has been set at 6,080 feet. So one degree of latitude or longitude equals 60 nautical miles (or 70 land miles). Any location on earth is described by two numbers—its latitude and its longitude. If a ship’s captain wants to specify position on a map, these are the “coordinates” they would use. Think of position coordinates like you think of street addresses. When position coordinates are given, it’s just a way to pinpoint a place by identifying where lines of longitude and latitude intersect. This can be particularly helpful in the middle of the ocean where there are no visible landmarks. Coordinates are always read by stating the latitude first and the longitude second. One very famous set of position coordinates is latitude 41 degrees 33 minutes north, longitude 50 degrees 01 minute west. On April 14, 1912, this is where the ocean liner Titanic struck an iceberg in the northern Atlantic Ocean and quickly sank.