This youtube channel has a lot of dedicated introductory scientific playlists, but the latest one, Astronomy is my favourite. The host is just so enjoyable!
https://www.youtube.com/playlist?list=PL8dPuuaLjXtPAJr1ysd5yGIyiSFuh0mIL
https://www.youtube.com/playlist?list=PL8dPuuaLjXtPAJr1ysd5yGIyiSFuh0mIL