.astronomy – Not quite a conference (although they do have an unconference). They’ll have lots of talks from some very interesting speakers, and hacks too, all related to astronomy on the internet.
AstroHackWeek – “A week-long workshop that combines summer school and unconference” taking place in Seattle in August, 2017.
NASA Space Apps Challenge – Every year people get together all over the world for one of the largest hackathons in the Universe. And it’s not just for coders!