Crash Course Astronomy: Earth

Astronomy as a science is pretty tough to define these days. I actually point that out in the first episode of Crash Course Astronomy; if I observe Mars using my backyard telescope I'm doing astronomy, but what if I'm a professional scientist looking at isotope ratios in samples of atmospheric gas trapped in an air bubble from a Mars meteorite? That's maybe chemistry, or geology, or just planetary science. Where does astronomy start? With the Moon? Above the atmosphere? It's like asking where th...