Shamelessly appropriating Roma Victrix's idea about history channels on YouTube, this thread proposes to serve as a repository for science channels on YouTube. To begin:
Not surprisingly, PBS has a wide variety of science channels of which one offers these two as a soupçon.
PBS Eons, a gentle guide to all thing paleontological, anthropological, evolutionary, etc.
https://www.youtube.com/channel/UCzR...PHN9Zg7RML9EbA
PBS Space Time, a quite rigorous (no math though) series on physics, astrophysics, cosmology, astronomy, et alia
https://www.youtube.com/channel/UC7_...ThXybpVgjHZ_7g
For mathematics, there is Numberphile featuring mini-lectures from a countable infinity of mathematicians
https://www.youtube.com/channel/UCox...IDTYp3uz647V5A
(Frequently, supplementary material for a day's particular video will be found on its sister channel, Numberphile2.)
One more for now, then I'll shut up.
Another astronomy and physics channel, Anton Petrov offers accessible précis of the latest scientific research
https://www.youtube.com/channel/UCci...oIIMi-lfu8-cjQ
(As a bonus, if you watch his channel, you will be called a wonderful person.)