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CPL » Navigation » Form of the Earth

Great Circles

A Great Circle is a circle that has the centre of the earth as the centre of the circle, and will in effectively cut the world into two equal halves.

Great circles have some specific properties:

  • It is the largest circle that can be drawn on a sphere.
  • The direction is not constant.
  • The shortest distance between two points is part of the arc of a great circle.
  • Only one Great Circle can be drawn between 2 points.
Examples of Great Circles:
  • Meridians of longitude
  • Equator

Small Circles

Small Circles are similar to Great Circles except that they do not divide the earth into two equal parts and do not have the centre of the earth as the centre of the circle.

Eg. Parallels of Latitude

Rhumb Lines

  • These are lines that cut all meridians at the same angle.

  • Their direction is constant.

Is a rhumb line circle the shortest distance between 2 points?

Parallels of Latitude

  • The reference for latitude is the equator (0º latitude)
  • We measure latitude as an angular distance from the equator.
  • The south pole is 90ºS of the equator.
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