Longitude & Latitude & International Date Line

A key geographical question throughout the human experience has been, "Where am I?" In classical Greece and China, attempts were made to create logical grid systems of the world to answer this question. The ancient Greek geographer Ptolemy created a grid system and listed the coordinates for places throughout the known world in his book Geography. But it wasn't until the middle ages that the latitude and longitude system was developed and implemented. This system is written in degrees.

Latitude
• When looking at a map, latitude lines run horizontally.
• Latitude lines are also known as parallels since they are parallel and are an equal distant from each other. Each degree of latitude is approximately 69 miles (111 km) apart; there is a variation due to the fact that the earth is not a perfect sphere but an oblate ellipsoid (slightly egg-shaped).
• Degrees latitude are numbered from 0° to 90° north and south. Zero degrees is the equator, the imaginary line which divides our planet into the northern and southern hemispheres. 90° north is the North Pole and 90° south is the South Pole.
The Equator
• The equator is located at zero degrees latitude.
• The equator divides the planet into the Northern and Southern Hemispheres.
• The equator runs through Indonesia, Ecuador, northern Brazil, the Democratic Republic of the Congo, and Kenya, among other countries.
• It is 24,901.55 miles (40,075.16 kilometers) long.
• On the equator, the sun is directly overhead at noon on the two equinoxes - near March and September 21.
The Tropic of Cancer
• The Tropic of Cancer is located at 23.5° North of the equator.
• It runs through Mexico, the Bahamas, Egypt, Saudi Arabia, India, and southern China.
The Tropic of Capricorn
• The Tropic of Capricorn lies at 23.5° South of the equator.
• It runs through Australia, Chile, southern Brazil (Brazil is the only country that passes through both the equator and a tropic), and northern South Africa.

Longitude
• The vertical longitude lines are also known as meridians. They converge at the poles and are widest at the equator (about 69 miles or 111 km apart).
• Zero degrees longitude is located at Greenwich, England (0°). The degrees continue 180° east and 180° west where they meet and form the International Date Line in the Pacific Ocean.
• Greenwich, the site of the British Royal Greenwich Observatory, was established as the site of the Prime Meridian by an international conference in 1884.
• The Prime Meridian at zero degrees longitude and the line of longitude opposite the Prime Meridian (near the International Date Line) at 180 degrees longitude that divides the earth into the Eastern and Western Hemispheres.
• The Eastern Hemisphere consists of Europe, Africa, Asia, and Australia while the Western Hemisphere includes North and South American.
• Some place the boundaries between the hemispheres at 20° West and 160° East so as to not run through Europe and Africa.
• The International Date Line divides Two Days on the Earth's Surface

The International Date Line
• While the equator divides the earth into Northern and Southern Hemispheres, it is the Prime Meridian at zero degrees longitude and the line of longitude opposite the Prime Meridian (near the International Date Line) at 180 degrees longitude that divides the earth into the Eastern and Western Hemispheres.
• The Eastern Hemisphere consists of Europe, Africa, Asia, and Australia while the Western Hemisphere includes North and South American. Some place the boundaries between the hemispheres at 20° West and 160° East so as to not run through Europe and Africa.
• The International Date Line divides Two Days on the Earth's Surface.
• While the world is divided into 24 time zones, there has to be a place where there is a difference in days, somewhere the day truly "starts" on the planet.
• Thus, the 180° line of longitude, exactly one-half way around the planet from Greenwich, England and 0° longitude is approximately where the International Date Line is located. Cross the line from the east to the west and a day is added. Cross from west to the east and a day is subtracted.
• Without the International Date Line, people who travel west around the planet would discover that when they returned home, it would seem as though an extra day had passed. This situation actually happened to Magellan's crew when they returned home after their circumnavigation of the earth.

• The International Date Line is not a straight line, either. Since its beginning, it has zigzagged to avoid spitting apart countries into two days. It bends through the Bering Strait to avoid placing far northeastern Russia in a different day than the rest of the country. Unfortunately, tiny Kiribati was split. In 1995 the island country of Kiribati decided to move the International Date Line. Since the line is simply established by international agreement and there are not treaties or formal agreements associated with the line, most of the rest of the world followed Kiribati and moved the line on their maps. Most recent maps show the change and you'll see the big panhandle zigzag which keeps Kiribati all within the same day. Now eastern Kiribati and Hawaii, which are located in the same area of longitude, are a whole day apart.