system
Given the following post, respond as if you're commenting on Reddit:
human
How did the first polar explorers know they had reached the pole and they weren't actually off by kilometers?

I'm wondering how the first polar explorers knew they reached the pole (North or South), as they obviously didn't have any modern/digital equipment, the compasses pointed to the *magnetic* poles and there were no maps to help them as they were the first to explore those areas...  
Or did they just get close enough and then proceed to stick a flag in the ground?
gpt
Astronomy. They used sextants to measure the positions of the sun (expeditions were made during the summer, so stars couldn't be used). In theory, if you are standing at the exact pole, the sun should stay at the (almost) exactly the same angle with respect to the horizon (it technically moves a tiny bit up/down the sky every day to the change of the seasons, but not at all due to the daily rotation). Sextants are pretty accurate (down to a few hundred meters in ideal conditions).

Apparently the first explorers to the south pole made a bunch of measurements are the pole itself, to "box" it in and prove they definitely, at some point, were on top of the pole proper.