A [b]great circle[/b], also known as an [b]orthodrome[/b], of a [url=https://en.wikipedia.org/wiki/Sphere]sphere[/url] is the intersection of the sphere and a [url=https://en.wikipedia.org/wiki/Plane_(geometry)]plane[/url] that passes through the [url=https://en.wikipedia.org/wiki/Centre_(geometry)]center point[/url] of the sphere. A great circle is the largest circle that can be drawn on any given sphere.[br][br]The grear-circle distance or orthodromic distance is the shortest distance between two points on the sphere. Suppose two points [math]\left(\varphi_1,\lambda_1\right),\left(\varphi_2,\lambda_2\right)[/math] on the sphere. Orthodromic distance is [i]R.w [km][/i], where R = 6378 km and[br][center][math]\cos w=\sin\varphi_1\sin\varphi_2+\cos\varphi_1\cos\varphi_2\cos\left(\lambda_2-\lambda_1\right)[/math][/center]Problem: Measure the shortest air distance from London (51°N 0°) to  Buenos Aires (–34°S -60°W). [br]As a reference surface use sphere with radius R = 6 378 km.

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