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

Latitude is easy to work out with a sextant. An almanac will tell you the current declination (latitude) of the sun (or other visible object) and you can measure how high it appears above the horizon with a sextant. Close to the pole you don’t even have to wait for noon. With practice it’s not too hard to do better than a mile in accuracy. You won’t have a sea horizon but you’re on land or ice so you can use an artificial horizon (measure the angle between the sun and its reflection on a liquid surface).