How do we know precisely the locations of the geographic poles? And how did we know our location relative to them before GPS?

Question

Basically, how can we measure the Earth’s rotational axis accurately enough to be able to erect a physical [pole](https://external-content.duckduckgo.com/iu/?u=https%3A%2F%2Fantarctic-logistics.com%2Fwp-content%2Fuploads%2F2016%2F08%2Fdestination-south-pole-1.jpg&f=1&nofb=1) that goes through it? And how did expeditions in the early 20th century know when they successfully reached the poles?

In: Other

Answer 1

Early expeditions likely used the magnetic poles. Failing that, however, we know the locations of the poles relative to the magnetic poles. Using some geometry, we can find the direction to the actual pole if we know roughly where we are and what direction the magnetic pole is in. As to how we can precisely measure the poles, the simplest thing I can think of is the [gyrocompass](https://en.m.wikipedia.org/wiki/Gyrocompass) . This is a device that measures the rotation of the Earth and uses it to tell us what direction North is.