The Axioms of Spherical Geometry Exploration

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  • Objective: Understand the axioms of spherical geometry.

The axioms of Euclidean geometry give us the basic statements from which the rest of Euclidean geometry can be deduced. They basically describe the behavior of lines, segments, circles, angles and parallel lines.

Below write down the respective axioms for spherical geometry.

Remember that the role of lines is played by the great circles - also known as geodesics - in spherical geometry.

A geodesic on a sphere


Euclidean Geometry: Any two points can be joined by a straight line. (This line is unique given that the points are distinct).

Spherical Geometry:
Case 1: Points P and Q are not antipodal.

Case 2: Points P and Q are antipodal.


Euclidean Geometry: Any straight line segment can be extended indefinitely in a straight line.


Euclidean Geometry: Given any straight line segment, a circle can be drawn having the segment as radius and one endpoint as center.


Euclidean Geometry: All right angles are congruent.

Parallel Lines

Euclidean Geometry: Through a point not on a given straight line, one and only one line can be drawn that never meets the given line.