Shortest Arc on a Sphere (Great Circle Minor Arc)

Shortest Arc on a Sphere (Great Circle Minor Arc)
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2015-10-10 12:34
In collections On Sphere
This GeoGebra example demonstrates the construction of the shortest path between two points on a sphere, which is the minor arc of the great circle passing through them. It illustrates the concept of geodesics on a spherical surface, emphasizing that the shortest arc lies on the intersection of the sphere with a plane through the sphere's center. The construction uses commands such as Sphere, PointIn, Point, Line, Plane, IntersectPath, CircumcircleArc, Tangent, OrthogonalLine, and Intersect to build the sphere, define points A and B, create the central plane, and generate the circular arc. Auxiliary tangents and intersection points help verify the minimality of the arc. This resource is suitable for high school or undergraduate students studying solid geometry, spherical trigonometry, or spatial analytic geometry, and serves as a visual aid for understanding geodesics and great-circle navigation.

GeoGebra Commands & Parameters

  1. Sphere((0, 0, 0), 3) → a
  2. PointIn(a) → A
  3. PointIn(a) → B
  4. Point(xAxis) → C
  5. Line(C, zAxis) → b
  6. Point(b) → D
  7. Plane(A, B, D) → c
  8. IntersectPath(c, a) → d
  9. Point(d) → M
  10. CircumcircleArc(B, M, A) → e
  11. Tangent(B, e) → f, g
  12. Tangent(B, d) → h, i
  13. Tangent(A, d) → j, k
  14. Point(j) → E
  15. Point(f) → F
  16. OrthogonalLine(E, f, space) → l
  17. OrthogonalLine(F, j, space) → m
  18. Line(B, l) → n
  19. Line(A, m) → p
  20. Intersect(n, p) → G

AI Drawing Prompt Reference

Draw a sphere with radius 3 centered at the origin. Place two random points on the sphere. Pick a point on the x-axis and draw a line through it parallel to the z-axis, then place a point on that line. Use the two sphere points and this auxiliary point to define a plane, which intersects the sphere in a great circle. Choose a point on this great circle, then construct a circular arc through the two sphere points and this chosen point, representing the shortest path on the sphere. Next, draw tangents to this arc at both sphere points, and also a tangent to the great circle at one of them. Place points on these tangents, construct lines through them perpendicular to the tangents in space, and find the intersection of these two perpendicular lines to help verify the minimality of the arc.
The prompt above was compiled from the original drawing commands and is for reference only.