Discover the Major Lines of Latitude and Longitude on a World Map

The Equator, Tropics, and Prime Meridian

Equator monument
The Mitad del Mundo (Middle of the World) Monument, in Pichincha, Ecuador, marks the Equator. John Elk III / Getty Images

Three of the most significant imaginary lines running across the surface of Earth are the equator, the Tropic of Cancer, and the Tropic of Capricorn. While the equator is the longest line of latitude on Earth (the line where Earth is widest in an east-west direction), the tropics are based on the sun's position in relation to Earth at two points of the year. All three lines of latitude are significant in their relationship between Earth and the sun. Running in the opposite direction, north-south, the Prime Meridian is one of the most important lines of longitude on Earth.

The Equator

The equator is located at zero degrees latitude. 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 km) long. On the equator, the sun is directly overhead at noon on the spring and fall equinoxes—around March 21 and September 21 each year. The equator divides the planet into the Northern and Southern Hemispheres. On the equator, the length of day and night are equal every day of the year: Day is always 12 hours long, and night is always 12 hours long.

The Tropic of Cancer and The Tropic of Capricorn

The Tropic of Cancer and the Tropic of Capricorn each lie at 23.5 degrees latitude. The Tropic of Cancer is located at 23.5 degrees north of the equator and runs through Mexico, the Bahamas, Egypt, Saudi Arabia, India, and southern China. The Tropic of Capricorn lies at 23.5 degrees south of the equator and runs through Australia, Chile, southern Brazil (Brazil is the only country that passes through both the equator and a tropic), and northern South Africa.

The tropics are the two lines where the sun is directly overhead at noon on the two solstices—about June 21 and December 21. The sun is directly overhead at noon on the Tropic of Cancer on June 21 (the beginning of summer in the Northern Hemisphere and the beginning of winter in the Southern Hemisphere), and the sun is directly overhead at noon on the Tropic of Capricorn on December 21 (the beginning of winter in the Northern Hemisphere and the beginning of summer in the Southern Hemisphere).

The reason for the location of the Tropic of Cancer and the Tropic of Capricorn at 23.5 degrees north and south respectively is due to the axial tilt of the Earth. The Earth is tilted 23.5 degrees from the plane of the Earth's revolution around the sun each year.

The area bounded by the Tropic of Cancer on the north and Tropic of Capricorn on the south is known as the "tropics." This area does not experience seasons, because the sun is always high in the sky. Only higher latitudes, north of the Tropic of Cancer and south of the Tropic of Capricorn, experience significant seasonal variation in climate. Realize, however, that areas in the tropics can be cold. The peak of Mauna Kea on the big island of Hawaii stands nearly 14,000 feet above sea level, and snow is not unusual.

If you live north of the Tropic of Cancer or south of the Tropic of Capricorn, the sun will never be directly overhead. In the United States, for example, Hawaii is the only location in the country that is south of the Tropic of Cancer, and it is thus the only location in the United States where the sun will be directly overhead in the summer.

Prime Meridian

While the equator divides 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 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 America. Some geographers place the boundaries between the hemispheres at 20 degrees west and 160 degrees east so as to not run through Europe and Africa. Unlike the equator, the Tropic of Cancer, and the Tropic of Capricorn, the Prime Meridian and all lines of longitude are completely imaginary lines and have no significance with regard to Earth or to its relationship with the sun.