This video from Vsauce discusses cardinal numbers, the cardinality of the natural numbers (aleph null), ordinal numbers, and all sorts of infinities.
Schwarzschild radii, gravitational lensing, orbiting a black hole, photon sphere, falling into a black hole, tidal forces, spaghettification, singularities, wormholes, dumbholes (acoustic black holes), time dilation, length contraction
Sound in space, sound picked up by one of the Voyager probes as it passed through Saturn’s rings. Plus some other things.
A quick video showing the creation of the Moon from a collision, and an explanation of the tilt of Earth’s orbit. Also some UK geography.
How refraction and reflection of light generates rainbows and double rainbows.