# When did ocean sailors realise that the shortest path on the globe is a great-circle? [closed]

The shortest path between two points on a sphere (and thus with limited applicability also on earth) is a great-circle. I.e.

A great circle is the intersection of the sphere and a plane which passes through the center point of the sphere.

On a sphere, great circles are geodesics. This is the reason why air planes crossing the Atlantic often pass over Iceland. The theoretical proof was given by Bernhard Riemann around 1900.

When did the people that sailed the big oceans started to realise that? Did they realise it at all?

Christopher Columbus always landed in the Caribbean and his path looks as if he wasn't aware of it, but there may be many other reasons for that (winds, passing known islands). Maybe this started only with the beginning of steamboats??

EDIT: @Mike gives an important hint: It depends very much on the maps they used, here is an example of the great-circle from NY to London, in Mercator (upper panel) and Gnomonic (lower panel) projection. In the latter, all straight lines are great circles.

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When? Good question, but if you think the earth is round, you have globular maps, and then just stretch a string. Those sailors were no less smart than we are today, and they certainly understood winds, tides, & navigation. – Mike Dunlavey Apr 30 '11 at 20:43
They had a lot of problems measuring longitude due to lack of precise clocks! en.wikipedia.org/wiki/History_of_longitude – Sklivvz Apr 30 '11 at 23:39
A map on a globe. Stretch a string on it, and it's a great circle. – Mike Dunlavey May 1 '11 at 14:38
I would suggest that any sailor looking at a globe would understand geodesics pretty quickly. But there are other contributions to a successful voyage beyond distance: safety, supplies, etc. The Phoenecians are known to have traveled within sight of shore, for example: en.wikipedia.org/wiki/File:PhoenicianTrade.png – John Craft May 1 '11 at 21:19
Among other considerations there are different prevailing winds at different latitudes. Even today sailors do not take the shortest routes between two points. There are also good reasons to stay close to land as long as practical. – DJClayworth May 30 '11 at 16:22

## closed as off topic by Fabian♦Mar 19 at 7:29

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