Orbital mechanics because I take Kerbal Space Program way too seriously. If anyone wants to geek out about this and take a look at my code, get in touch.
Woodworking because it's a nice balance to working with computers. I work almost exclusively with hand tools.
I took a few courses of astronomy at Helsinki university, but mostly I've studied on my own. I did watch Leonard Susskind's lectures on classical mechanics but did not any online courses.
Check out my related project, it contains all the orbital mechanics you need to write your own Kerbal Space Program clone (look around in the branches):
https://github.com/rikusalminen/twobody
Woodworking because it's a nice balance to working with computers. I work almost exclusively with hand tools.