Astronomy buffs should enjoy Chris Impey’s free online courses offered through Udemy and Coursera. One interesting feature of the Astronomy State of the Art course is his regular online office hour where he takes questions submitted in real time as well as by email. The questions are invariably very good, spanning terrestrial, planetary, galactic, and cosmological topics. Impey takes time to respond thoroughly. The live sessions are broadcast on a Google Hangout and archived on Youtube. Here’s a collection of them.