I volunteer at a group that has restored the oldest German radio telescope. We are now at a point where we want to invite interested amateur astronomers and school children to workshops. I'm currently thinking about the most interesting things to do in a certain timeframe, say, half a day.
What would you consider most important phenomena to show in a hands-on workshop with interested, not-too-amateur visitors?
Regarding our instruments: We can do continuum and spectroscopical measurements at 1.4 GHz (hydrogen line) on our 25 m dish and have several optical telescopes, up to an 11 inch Cassegrain. Additionally, we are thinking about using our parallactically-mounted 10 m dish (currently with a 10 GHz receiver) and perhaps buying a H-alpha-scope.