Mathematics
The Geodesic Equation on a Sphere and Great-Circle Navigation
Quick fact
The shortest path between two points on a sphere is always an arc of a great circle—the circle formed by cutting the sphere with a plane that passes through its center. Every meridian on Earth is a great circle, but the equator is the only parallel that is one.
Why this is interesting
Have you ever wondered why flight paths on a map often look like gentle arcs rather than straight lines? On a globe, the shortest route between two cities is actually a curve that may surprise you.