You can see Polaris with the right equipment, meaning an eye adjusted to darkness, and a filter on your optics. It's always above the horizon in the Northern he

You can see Polaris with the right equipment, meaning an eye adjusted to darkness, and a filter on your optics. It's always above the horizon in the Northern hemisphere, even during the day. (Same goes for the Southern cross in the Southern hemisphere.) Polaris is important because it doesn't move, relative to the rest of the sky rotating around it. You measure the angle from Polaris to geodetic "up" and that's the complimentary angle to your latitude. There is no complex math, just 90-x=y If you have the time in London, and can observe the sun at its peak (solar noon) then you have longitude (after converting hours to degrees, and keeping minutes and seconds). Or with an almanac, you can measure pretty much any known ID'd star or the sun at any time, and look up longitude from that. Reinventing the wheel isn't needed, it's been the same process for centuries.