UC Berkeley SETI researcher Andrew Siemion and his colleagues have put an upper limit on the number of civilizations in our galaxy that are capable of giving us a call. He’ll explain their reasoning and provide other search updates. Emily Lakdawalla is never at a loss for great space images. This time they include watching our moon transit the Earth, and a surprisingly beautiful scoopful of Martian dirt. Bruce Betts would rather not talk about the bad, bad things that can happen at high altitude, but he’s happy to tell us about the night sky and provide a Random Space Fact. Bill Nye returns next week.