Definition

1. Noun:
   • A circular line on the surface of a sphere formed by intersecting it with a plane passing through the sphere's center: A "great circle" is the largest possible circle that can be drawn on a sphere. Its plane cuts the sphere into two equal hemispheres, and its center is coincident with the center of the sphere.

Usage

• The term "great circle" is used primarily in geometry, geography, astronomy, and navigation.
• It describes a specific geometric construct, not a general large circle. Any circle on a sphere whose radius is equal to the sphere's radius is a great circle.
• In practical contexts like Earth, great circles represent the shortest path between two points on the sphere's surface, a principle used in great-circle navigation.

Examples

• Noun:
  • The equator is a great circle of the Earth, equidistant from the poles.
  • Navigators plot courses along great circles to minimize travel distance over the ocean.
  • In geometry, every line of longitude (meridian) on a globe forms a great circle.

Advanced Usage

• "Great circle distance": The shortest distance between two points on the surface of a sphere, measured along the arc of a great circle.
  • The great circle distance between New York and London is much shorter than it appears on a flat map.
• "Great circle route": A route, especially for ships or aircraft, that follows the arc of a great circle.
  • The pilot adjusted the flight path to follow a more efficient great circle route.

Variants and Related Words

• Small circle (n): A circle on the surface of a sphere whose plane does not pass through the sphere's center. All parallels of latitude except the equator are small circles.
  • The Arctic Circle is a small circle on the Earth's surface.
• Great-circle sailing (n): The practice of navigating a vessel along a great circle route.
• Orthodrome (n): Another term for a great circle, used in more technical contexts.

Synonyms

• Orthodrome: (Technical) A great circle on a sphere.
• Geodesic: (In the context of a sphere) The shortest path between two points, which is an arc of a great circle.

Related Concepts (Not Phrasal Verbs or Idioms)

• Rhumb line: A path of constant bearing, which crosses all meridians at the same angle. Unlike a great circle route, a rhumb line is not the shortest distance but is easier to navigate.
• Great circle chart: A navigational chart on which great circles appear as straight lines, used for planning routes.

Noun

1. a circular line on the surface of a sphere formed by intersecting it with a plane passing through the center