From the maps they show, it’s pretty clearly a great circle (the obvious meaning for “straight line” on the surface of a sphere), not constant bearing.
Whoops, turns out I didn't actually understand what "constant bearing" meant. What I actually meant was "no rudder/steering" which is exactly what people would imagine as travelling in a straight line.
Obvious perhaps, in a mathematically idealised system that's idealised according to axioms that are unstated ... a non-equitorial latitudinal line on a sphere is straight.
What sort of constant bearing - magnetic bearings will vary along a map-based bearing. There's an arbitrary choice involved. We're probably not looking at changes in sea-level that put us off line - is a necessarily idealised system in which the question makes sense.
From the maps they show, it’s pretty clearly a great circle (the obvious meaning for “straight line” on the surface of a sphere), not constant bearing.
Whoops, turns out I didn't actually understand what "constant bearing" meant. What I actually meant was "no rudder/steering" which is exactly what people would imagine as travelling in a straight line.
A constant bearing actually gives a Rhumb line: https://en.wikipedia.org/wiki/Rhumb_line
Don't apologize. Your use is perfectly correct, you're obviously not referring to compass bearing.
Obvious perhaps, in a mathematically idealised system that's idealised according to axioms that are unstated ... a non-equitorial latitudinal line on a sphere is straight.
Walk (or drive, or sail) without turning and you’ll follow a great circle.
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What sort of constant bearing - magnetic bearings will vary along a map-based bearing. There's an arbitrary choice involved. We're probably not looking at changes in sea-level that put us off line - is a necessarily idealised system in which the question makes sense.
But, unless you are passing over a pole, a great circle doesn't use a constant bearing.