The Great Circle - Flights to America

 We climbed up to High Cup Nick in the Pennines, Here's the view looking south onto a cloud inversion around the Howgills. can you spot the vapour trail in the middle of the picture? It's a truism in these parts that these planes are going to America because the shortest route is up and over. It's called the Great Circle. I got out my atlas and traced out the route from London to San Francisco - see below. On the flat map it would go west over Bristol.

 But then I got my globe out. On a curved suface, the shortest route will be different. It's easy to do by pulling a string tight between two points as shown below for the same route.  A Great Circle is drawn between two points on the surface of the sphere and is part of a continuous circle round the globe centred on the middle of the Earth. It's like an orbit in that regard.

                                       
 In close up, it does indeed go up and over Cumbria.

I used this popular website to test my theory http://www.flightradar24.com/ but I found that rather a lot of the flights over Cumbria are actually to Glasgow! There must be more of those than flights to LA. The globe showed me that the quickest way to New York is actually out over Bristol.