Strange circle stuff.
(Some people have commented that the audio is really low. Unfortunately I haven't found a way to fix it without re-uploading the whole video, but your feedback will be taken on board for the next video! Also to everyone begging for more content, I’m currently in the middle of university study, but I’m hoping to do my next video around the end of November.)

This video is my submission for 3blue1brown's Summer of Math Exposition 2021:
https://www.3blue1brown.com/blog/some1
For more videos created by others for SoME1, here's a playlist:
   • Summer of Math Exposition Youtube Videos  

Some more detail on the stereographic projection:
http://www.geom.uiuc.edu/docs/doyle/m...
https://www.cut-the-knot.org/pythagor...
http://www.ams.org/publicoutreach/fea...

Animations were made in Manim:
https://www.manim.community