For example, if I were in Tangier, Morocco, and wanted to fly to Whangarei, New Zealand (the antipode on the globe) – wouldn’t it be about the same time to go up instead of across?
ETA: Thanks so much for the detailed explanations!
For those who are wondering why I picked Tangier/Whangarei, it was just a hypothetical! The-Minmus-Derp explained it perfectly: *Whangarei and Tangier airports are antipodes to the point that the runways OVERLAP in that way – if you stand on the right part if the Tangier runway, you are exactly opposite a part of the Whangarei runway, making it the farthest possible flight.*
In: 2270
Great Circles are the most distance efficient route for travelling across the surface of a sphere. This is a circle with the centre of the earth as its centre (think of the equator, but rotated so the start and end points are on the same circle.
It’s the same concept as a straight line on a 2D surface, but takes the 3D curvy nature into account.
If somewhere is a true antipode, then there could be more than 1 great circle – in this case, you’d fly the route that was most wind efficient (Flying West to East for example) and that kept you closest to airports for diversion.
There’s a cool site for showing great circle maps – [Here’s one for Tangier to Whangarei](http://www.gcmap.com/mapui?P=TNG-WRE)
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