Definition
A course flown along the shortest path between two points on the surface of the Earth. A great circle is any circle on the Earth's surface whose center is the center of the Earth, and the arc of such a circle between two points is the shortest distance between them. Except for flights along the equator or directly along a meridian, a great circle course continually changes its compass direction as it is flown.
Plain English
The shortest possible route between two points on the globe. Because the Earth is round, this route looks curved on a flat map and requires the pilot's heading to change gradually along the way.
Context Anchor
Seen in flight planning and navigation, especially for long-distance flights where the shortest route matters.
Derivation
A 'great circle' is any circle drawn around a sphere whose plane passes through the sphere's center, dividing it into two equal halves. The equator is a great circle; so is any line of longitude paired with its opposite. 'Course' comes from the Latin cursus, meaning 'a running' or 'path traveled.' Together the term simply means the path along the largest possible circle that can be drawn on the Earth between two points.
Why Pilots Care
Following a great circle saves significant distance, fuel, and time on flights spanning oceans or high latitudes compared to constant-heading routes.
Analogy
Stretch a string tight between two points on a globe. The path the string follows is a great circle. It looks straight on the globe but curved when the same path is drawn on a flat map.
Intuition Check
“Great” does not mean excellent here; it means the largest kind of circle that can be drawn on a globe. “Course” does not mean a class; it means the intended path the aircraft will follow.
Example Sentence 1
The flight plan from New York to London follows a great circle course that arcs north over Newfoundland rather than tracking due east.
Example Sentence 2
The navigation computer displayed the great circle course as a gently curving track across the North Atlantic.