Equator

The equator is an imaginary line that circles the middle of the Earth. It splits our planet into two halves, called the Northern and Southern Hemispheres. This line is located at 0 degrees latitude and is about 21,639 nautical miles around, or 40,075 kilometres.

On and near the equator, the sunlight is very strong around noon all year. The sun appears almost straight up in the sky, which helps keep temperatures steady. During special days called equinoxes, which happen around March 20 and September 23, the sun shines directly over the equator, giving everywhere on Earth almost exactly 12 hours of day and 12 hours of night.

The equator is not just for Earth. Any round object that spins, like a planet, has an equator too. It is the line that is exactly halfway between the north and south poles and runs perpendicular to the object's spinning axis.

Etymology

The word "equator" comes from an old Latin phrase meaning "circle equalizing day and night." It was used to describe the line that makes day and night roughly the same length everywhere along it.

Overview

The equator is an imaginary line around the middle of Earth that splits it into two halves: the Northern and Southern Hemispheres. It is located at 0° latitude and is one of five important lines around Earth. Unlike other lines, the equator is a special kind called a great circle, which means it goes through the center of our planet.

When the Sun is directly above the equator, it is called an equinox, and this happens twice a year in March and September. Places on the equator see the Sun rise and set very quickly because the Sun’s path is almost straight up and down. Days and nights are almost the same length all year. Earth also bulges a little bit at the equator, making it wider here than at the poles.

Geodesy

Further information: Earth ellipsoid and Reference ellipsoid

Precise location

The exact spot of the equator moves a little because Earth's spinning axis shifts about 9 metres each year. Long ago, between 48 and 12 million years back, the equator was in very different places. Ocean currents left clues in rocks showing these changes. Volcanoes also give hints about how Earth's axis moves over time.

Exact length

Main article: Earth's circumference

Scientists have measured the distance around Earth at the equator very carefully. Using special tools, they found it to be about 40,075 kilometres or 24,902 miles long. Earth isn't a perfect ball; it's slightly squashed, which makes the equator a bit longer than paths going over the poles. The actual shape of Earth's surface makes finding the exact length tricky, but scientists keep improving their measurements.

Equatorial countries and territories

The equator passes over land and sea in several places around the world. It crosses through eleven countries, starting from the Prime Meridian and moving east. Indonesia has the longest stretch of the equator running through it.

The equator also touches the waters near three other countries: Maldives, Kiribati, and the United States. Even though it’s in the name, Equatorial Guinea does not actually touch the equator, though its island of Annobón is close to it.

Equatorial seasons and climate

Main articles: Season and Effect of Sun angle on climate

Further information: Tropics

The equator affects how seasons and climate work on Earth. Because Earth tilts on its axis, the Northern and Southern Hemispheres take turns facing more toward or away from the Sun during the year. The side facing the Sun gets more sunlight and experiences summer, while the other side gets less sunlight and experiences winter.

Near the equator, the change in sunlight throughout the year is different from places farther north or south. The equator gets the most direct sunlight during the equinoxes, when day and night are about equal in length all over Earth. Even during the solstices, when one pole faces the Sun more directly, temperatures near the equator stay warm because the tilt of Earth isn’t enough to greatly reduce the Sun’s strength. This means that places near the equator don’t have big temperature changes like other parts of the world do. Instead, they usually stay quite warm all year.

Line-crossing ceremonies

Main article: Line-crossing ceremony

Many sailors and passengers celebrate when they cross the equator for the first time. These celebrations can be fun and exciting, often including games and playful traditions. On some ships, people might dress up as a famous sea character to make the event special and memorable for everyone.