What are great circles?

Great circles are defined as circles on the surface of a sphere, such as the Earth, that have planes which pass through the center of that sphere. This property means that a great circle represents the shortest distance between any two points on the surface. Routes taken by aircraft often utilize great circles for more efficient navigation, as these paths allow for shorter travel distances over the globe.

In contrast, other options do not capture this fundamental aspect of great circles. For example, the notion that great circles do not pass through the Earth's center misdefines their geometric property. Additionally, lines of latitude, while they can be thought of as circles, are not great circles unless they are at the equator, as they do not extend through the center of the Earth. Furthermore, rhumb lines, which represent paths of consistent bearing, do not inherently relate to the characteristics of great circles, as they do not cut meridians at right angles in all instances. Thus, the correct definition of great circles lies in their unique relationship with the center of the Earth.