I was reading Wikipedia with two browser tabs open. One page was on bretwalda; the other page was on spherical harmonics. I have no idea how I ended up researching both simultaneously.
Things I learnt. Bretwalda. Wynn, yogh, eth, thorn, ash. Spherical harmonics. Fourier analysis (transformation and synthesis). Deferent and epicycle. How to make compound words from machine, mechanic, machinist. Must watch “Ancient Astronomy” from The Great Courses (the library has a subscription). Must find more ways of describing an artisan.