Tell me more ×
Skeptics Stack Exchange is a question and answer site for scientific skepticism. It's 100% free, no registration required.
up vote 8 down vote favorite

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??

Routes of Columbus, actually the first one is quite close to a great circle

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.

NY to London great circles, two different projections

share|improve this question
1  
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
1  
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
1  
A map on a globe. Stretch a string on it, and it's a great circle. – Mike Dunlavey May 1 '11 at 14:38
2  
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
1  
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
show 4 more comments

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

Questions on Skeptics Stack Exchange are expected to relate to scientific skepticism within the scope defined in the FAQ. Consider editing the question or leaving comments for improvement if you believe the question can be reworded to fit within the scope. Read more about closed questions here.

1 Answer

up vote 8 down vote accepted

In 1594, an English explorer named John Davis published a book entitled The Seaman's Secrets [note- archive.org link, the original site seems to have been reorganised] in which he states that:

The third is a great Circle Navigation, which teacheth bow upon a great Circle, drawn between any two places assigned (being the only shortest way between place and place) the Ship may be conducted and to performed by the skilful application of Horizontal and Paraboral Navigation.

So it was definitely known as early as 1594. Now, the real trick is being able to navigate a great circle without a chronometer...

share|improve this answer
this is an interesting answer and suggests that the concept of great circle journeys was know very early. It would be interesting to know when the navigators actually applied this. So far this is the only and best answer though. Accept. – Sebastian Jun 14 '11 at 7:17

Not the answer you're looking for? Browse other questions tagged or ask your own question.