In The Martian, the astronauts describe the incoming storm's movement in terms of bearings but surely the use of bearings would require a 'north'? I understand that Mars does not have a magnetic north and so I wonder how location and navigation are described?


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"North" or "true North" on Earth usually refers to the direction of the point where the vector about which the Earth rotates emerges from the surface (the North Pole). If you look at a globe, it's where the sphere is attached to the stand on the top, and about which it spins.

Magnetic North moves around, and so isn't a good point of reference. For navigating, when you use a compass to find magnetic, you than have to adjust based on your location to where "true North" is relative to magnetic North.

Mars also rotates about a fixed axis, so we just use the same system. The weak magnetic field doesn't change things, though it would make a compass pretty useless. But Matt Damon could presumably figure out North by just observing where the Sun rose.

ETA: Just dug up my copy of the book of "The Martian", and that's indeed the solution the author came up with for his protagonist. He keeps track of where the moon (Phobos) rises and sets.


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