Why Planes Don't Fly in a Straight Line

If you have ever watched the little plane on the screen during a long flight, you may have noticed something strange. A flight from London to Los Angeles doesn't go straight across the Atlantic on the map. Instead, it travels far to the north, near Iceland and over Greenland. Then it comes down across Canada. It looks like a very long way around. In fact, it's close to the shortest way.

The problem isn't the route. It's the map. The Earth is round, but the maps on our walls and screens are flat. To make a round surface flat, mapmakers have to stretch it. On the most common world maps, they stretch the areas near the poles the most. That's why Greenland can look almost as big as Africa, although Africa is about fourteen times larger.

You can see this for yourself with an orange and a piece of string. With a pen, draw two dots on the top half of the orange, far apart from each other: one for London and one for Los Angeles. Now hold one end of the string on each dot and pull it tight. A tight string always finds the shortest path. Look where it goes. It doesn't stay level between the dots. It bends up toward the top of the orange, closer to the "North Pole" than either city.

On a ball, the shortest path between two points is always part of a great circle, a circle as big as the ball itself, like the equator. If you could peel the orange and press the skin flat, the line of the string would become a curve. That's exactly what you see on the screen in the plane. The route that looks longer on a flat map is shorter in the real sky.

Pilots don't follow the great circle exactly, though. High above the North Atlantic, there are fast rivers of wind called jet streams, which usually blow from west to east. Flights going east, from North America to Europe, try to ride them, and they can arrive around an hour earlier than flights going the other way. Flights going west try to stay out of their way. Because the winds move, new routes across the ocean are planned every day.

Try it yourself: take a ball and a string, and choose two cities in the north that are far apart. Pull the string tight and see which way it bends. The next time you fly, you'll know why the little plane on the screen seems to take the long way, even when it's taking the short one.