Final answer:
A great circle is the largest circle that can be drawn on a sphere, such as the Earth's equator. Meridians are examples of great circles that connect the poles. Airplane routes often follow great circle arcs for the most direct path.
Step-by-step explanation:
What is a Great Circle?
A great circle is the largest possible circle that can be drawn on a sphere. These circles are formed when a plane passes through the center of the sphere, bisecting it into two equal hemispheres. The Earth's equator is a familiar example of a great circle, equally dividing the planet into the Northern and Southern Hemispheres. Meridians, which connect the North and South Poles, are also great circles. They are perpendicular to the equator and intersect it at right angles. When traveling long distances across the Earth's surface, such as from Chicago to Rome, airplanes follow the arc of a great circle to ensure the shortest possible route.
The concept of great circles is also used in geometry and navigation, highlighting its versatility and significance.