system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Since magnetic north is not the same direction as true north, when and how did navigators figure this out, how did they compensate, and does the advent of GPS navigation render the magnetic compass completely obsolete?
gpt
> Since magnetic north is not the same direction as true north, when and how did navigators figure this out

Quoting Wikipedia here:

> The first expedition to reach the North Magnetic Pole was led by James Clark Ross, who found it at Cape Adelaide on the Boothia Peninsula on June 1, 1831. Roald Amundsen found the North Magnetic Pole in a slightly different location in 1903. The third observation was by Canadian government scientists Paul Serson and Jack Clark, of the Dominion Astrophysical Observatory, who found the pole at Allen Lake on Prince of Wales Island in 1947.

Navigators use a number of different tools. A sextant can be used to determine latitude by looking at stars, specifically Polaris. When explorers found the magnetic North Pole they found that their compasses spun because they couldn't find north. But a sextant measurement would have shown they weren't at true north or ~~0 degrees~~ 90 degrees latitude.

But navigators knew there was a deviation between compasses and true north for a while before that.

> how did they compensate, 

Once Magnetic north was discovered they could adjust, maps will often have the declination adjustment written on them that tells you how to adjust your compass to point to true north. But navigating up north is still a challenge because of it. Markers like Polaris are unaffected by magnetic north. Which doesn't really help when you have constant daylight during parts of the year.

> and does the advent of GPS navigation render the magnetic compass completely obsolete?

No, compasses are still widely in use and navigators and soldiers for example are still widely instructed on their use. A compass is tiny and doesn't need batteries so it's still a very useful tool.