[mc10]

Perhaps the HN headline doesn't match the article, but the instructions say:

> Imagine you begin a journey in Seattle WA, facing exactly due east. Then start traveling forward, in a straight line along the Earth’s surface.

where there isn't any wording saying "go east in a straight line".

[tacitusarc]

The most reasonable interpretation of this is to follow the latitudenal geodesic along its eastern path. You cannot claim that one geodesic is more “straight” than another in 3d Euclidean geometry, that is nonsense. But that is what the author does.

Edit: Ok, the latitudinal geodesic only exists at the equator, so the question is fundamentally impossible, with how the author defines a straight line.

[pdonis]

> the latitudenal geodesic

There is no such thing. A curve of constant latitude on Earth, except for the equator, is not a geodesic.

> You cannot claim that one geodesic is more “straight” than another in 3d Euclidean geometry

In terms of 3D Euclidean geometry, neither a curve of constant latitude on Earth's surface nor a great circle on Earth's surface is a straight line/geodesic. Both are curved.

If you restrict to the 2D surface of the Earth, a great circle is a geodesic but a curve of constant latitude, except for the equator, is not.