Also more generally, once upon a time a GPS (Formally GPS Receiver) was a device the size of say, a multimeter, with a big battery pack, a simple monochrome unlit LCD panel display, and a radio (later, more expensive units had several radios). The device is doing fancy mathematics, and just receiving GPS signals, even the metadata about where to look for GPS satellites in the sky is available, very slowly, over GPS. It has no other source of data.

So you'd buy one or turn it on after uncrating it in a foreign country, and it'd literally spend ten or fifteen minutes calibrating, figuring out what the time is, what satellites are on what frequencies and which are above the horizon before it could at last discern your position. This was amazing if you genuinely didn't know where you were e.g. "Hmm, a desert". But you'd never have used one to go shopping - it took far too long.

Today your phone has a GPS with lots of radios (so it can listen to every satellite at the same time) it always knows the rough time,and it uses the Internet to get public shared data rather than wait to receive it slowly from GPS.

If you hold up two polarized sheets and rotate them, they'll get progressively darker until no light passes through when they are perpendicularly aligned. YouTube should have some videos, it was a pretty entertaining physics lab experiment.