Great-circle distance

Great-circle distance is when you want to find out how far apart two places are on a round shape, like a ball. To measure it, you need to imagine a line that goes right through the center of the ball and touches both of the places you want to compare. This line is called a "great circle."

It's kind of like drawing a line from one side of a pizza to the other through the middle, instead of measuring the distance around the outside crust. The great-circle distance is the shortest distance between two points on a sphere.

This type of measurement is useful for things like aviation or shipping, where it's important to know the quickest way to get from one place to another. It can also be used in mapping and navigation systems.