The equator

Imagine a belt around the middle of the Earth.

That is where the Equator is. You cannot see it on the ground. It is a line we draw on maps and globes.

The Equator is an imaginary line that circles Earth around its middle. It is exactly halfway between the North Pole and the South Pole. You cannot see it on the ground, but it is drawn on globes and on many world maps.

The Equator is the line of 0 degrees latitude, the starting line for measuring how far north or south a place is. Everything north of it is in the Northern Hemisphere, and everything south of it is in the Southern Hemisphere.

National Geographic Education defines an equator as an imaginary line around the middle of a planet or other body, halfway between its north and south poles, at 0 degrees latitude. Encyclopaedia Britannica adds precision: Earth's Equator is a great circle, everywhere the same distance from the geographic poles and lying in a plane at right angles to Earth's axis.

That makes it the natural reference line for latitude, which is reckoned north and south from it. It divides Earth into the Northern and Southern Hemispheres. Unlike the prime meridian, which people had to agree on, the Equator is set by the positions of the poles themselves, so no one had to choose it.

The Equator goes all the way around the Earth.

It is very, very long. It would take a very long time to walk around it.

Earth is widest at its Equator. National Geographic gives the distance around Earth at the Equator as 40,075 kilometers (24,901 miles). From the Equator to either pole is about 10,000 kilometers, according to Britannica.

Earth is not a perfect ball. It bulges a little at the Equator because it spins. The bulge is about 43 kilometers, so the distance through Earth's middle is a bit bigger at the Equator than from pole to pole.

Earth's circumference at the Equator is about 40,075 km (24,901 miles), slightly longer than its polar circumference of about 40,008 km (Britannica). National Geographic gives the equatorial diameter as about 12,756 km and the polar diameter as about 12,714 km: an equatorial bulge of about 43 km, created by Earth's rotation.

The bulge has real effects. People at sea level near the poles are closer to Earth's center than people at sea level near the Equator, and sea levels are slightly higher near the Equator. It also produces a puzzle. National Geographic explains that the bulge pushes the summit of Mount Chimborazo in Ecuador farther from Earth's center, and calls it, not Everest, the highest point on Earth by that measure. Measured the usual way, from sea level, Everest (8,848 meters in National Geographic's figure) is far taller than Chimborazo (6,310 meters).

The Equator crosses land and sea.

One country is even named after it: Ecuador! The Equator also goes through Kenya and Indonesia.

The Equator crosses oceans and land. Ecuador, in South America, is named after the Equator, which runs through it. Its capital, Quito, sits just south of the line.

In Africa, the Equator crosses Kenya and Gabon. In Asia, Indonesia is a country of islands that lies across the Equator. Encyclopaedia Britannica describes all four as sitting on or across the line.

Encyclopaedia Britannica describes Ecuador as named after the Equator, which bisects it, with Quito lying just south of the line at 9,350 feet in an Andean valley. In Africa, Kenya is bisected horizontally by the Equator, and Gabon lies astride it on the Atlantic coast. In Asia, Indonesia occupies an archipelago that lies across the Equator and spans a distance equivalent to one-eighth of Earth's circumference.

These are only some of the countries the line crosses. National Geographic notes rocket-launching sites near the Equator, because Earth's spin gives a launch an extra push there: at the Equator the spin is about 1,670 kilometers per hour.

Near the Equator, the Sun is high in the sky.

Many places there are warm all year. Some have a wet season and a dry season instead of winter and summer.

Twice a year, at the equinoxes, the Sun passes directly over the Equator at noon. The rest of the year it is still nearly overhead. Britannica explains that this lets the Equator receive more sunlight energy over a year than places nearer the poles.

So many places near the Equator are hot, with little change from season to season. National Geographic notes that many have two seasons, wet and dry. The long, warm, rainy seasons help tropical rainforests grow, such as the Amazon in South America and the Congo rainforest in Central Africa.

At both equinoxes the Sun's rays strike the Equator at 90° at noon, and for the rest of the year they are nearly direct; Britannica notes that this lets the Equator receive more incoming solar radiation over a year than locations nearer the poles. Above the Equator lies the intertropical convergence zone, a belt of low pressure where trade winds converge and air rises, bringing frequent clouds, thunderstorms and heavy rain.

National Geographic describes equatorial regions as often hot with little seasonal variation, and notes that many equatorial communities recognize two seasons, wet and dry, rather than four. Rainforests such as the Amazon and the Congo grow there. Yet, it adds, humid equatorial regions are not the hottest places on Earth, because the water in the air cools it slightly.

Some places near the Equator are cool.

High mountains can be cold. Mount Kilimanjaro is near the Equator, and it has ice at the top.

Not every place on the Equator is hot and steamy. Height above sea level matters too. Mount Kilimanjaro in Tanzania is only about 330 kilometers from the Equator, but it is so high that its climate is cool and dry, with glaciers near the top.

The Andes Mountains of South America are another cool place near the Equator, where llamas, alpacas, vicuñas and guanacos live.

National Geographic stresses that not all equatorial regions are hot and humid. Mount Kilimanjaro, Tanzania, stands only about 330 km (205 miles) from the Equator, yet its elevation gives it cool, dry weather and alpine glaciers. The equatorial Andes are chilly too, and are known for their camelids: llamas, alpacas, vicuñas and guanacos.

The lesson is that latitude is one control on climate, not the only one. On the Equator, lowland rainforests such as the Amazon and the Congo and cold, high places such as the Andes all lie near the same latitude, so it is worth checking elevation, as well as latitude, before guessing what a place is like.

Near the Equator, day and night are about the same.

The Sun comes up in the morning. It goes down in the evening. It does this at nearly the same times all year.

In many places, summer days are long and winter days are short. Near the Equator, that hardly happens. The U.S. National Weather Service explains that if you live on or very close to the Equator, you get about 12 hours of daylight all year round, give or take a few minutes.

Sunsets are quick there too. National Geographic says that at the Equator the change from day to night takes only a few minutes.

Day length barely changes at the Equator. The National Weather Service notes that on or very close to the Equator, daylight stays within a few minutes of 12 hours all year, while the seasonal swing grows larger with distance from the Equator. On the two equinoxes, Britannica adds, day and night are of equal length everywhere on Earth.

National Geographic says the rising and setting of the Sun is fastest at the Equator, with the transition from day to night taking only a few minutes.