The Equator: Earth's Belt Line at 0° Latitude

Picture a rubber band stretched tight around the middle of a ball. This waist-high line, exactly the same distance from the top and bottom points (the North Pole and the South Pole), is the equator. Slice Earth in half with a flat plane that passes through its center and sits at a right angle to its spinning axis. The line that plane draws on the surface is the equator.

The equator isn't a visible line painted on the ground or the sea. But its location isn't picked at random by people. It's set naturally by Earth's rotation axis. People use this invisible line as an imaginary reference line for maps and navigation. Planes and ships use it as a starting point to find their way.

This line splits Earth into the Northern Hemisphere on top and the Southern Hemisphere on the bottom. Latitude is the measure of how far north or south you are on a map, and the equator is where it starts: 0 degrees latitude.

In a dark room, shine a flashlight straight at a wall. The light piles up in a small, bright spot. Now tilt the flashlight so it hits at a slant. The light spreads over a bigger area and looks dimmer.

Earth gets sunlight the same way. Near the equator, the sun's rays hit almost straight down from overhead all year long, so a huge amount of heat energy is packed into a small area. Near the poles, the light comes in at a slant and the heat is spread thin.

That's why places near the equator don't have the four seasons most of us know: spring, summer, fall, and winter. It stays hot all year. Strong sun heats the air, which rises fast and often drops sudden downpours called squalls. All that rain helps grow thick tropical rainforests.

Earth isn't a perfectly round ball. It spins once a day, and that fast spin creates centrifugal force that pushes the middle of the planet outward a little. The waist bulges.

This makes the equator the longest circle around Earth. Its total length is about 40,075 kilometers (about 24,901 miles). The distance from Earth's center to the surface at the equator is also about 21 kilometers (about 13 miles) farther than to the North or South Pole. In other words, Earth is a slightly flattened, squashed-sideways shape called an ellipsoid.

Also, day and night at the equator are close to 12 hours each all year. Because the atmosphere bends light, and because sunrise and sunset are counted from the top edge of the sun, the real daytime is a few minutes longer than 12 hours. The equator is also where Earth's surface spins fastest, so a rocket launched toward the east gets an extra boost from Earth's rotation. That's why some launch sites sit close to the equator, like Kourou in French Guiana. But the actual location of a launch site also depends on things like safety and territory.