O.k., I'm not sure how to phrase this, but I'm going to try. If I'm confusing in my question, just ask for a clarification. I want to know how detecting the source (or direction) of an interstellar signal works? Specifically, a theoretical signal sent from an alien civilization at us. For instance, if a signal is coming from another planet to the Earth, it would have to be hitting the whole planet, right? It's not like the signal is aimed right at our telescope. I mean, one way they identify possible intelligent interstellar communications is to cross-check telescopes hundreds of miles away to look for Doppler shift in the signal caused by the Earth's rotation. So we (the Earth) would be getting a signal on several telescopes simultaneously, so the signal has to be hundreds of miles wide right? Probably hitting the entire earth (it would have to, otherwise it'd be almost impossible for us to find in the first place). So if the signal is hitting the entire earth, how can we tell what direction it's coming from? For instance, I know that SETI points its telescopes at sun-like stars, but if the signal they're detecting is hitting the whole earth, why do they need to point at all? And why don't all the signals just get mixed up? I may be thinking about this all wrong, but I hope someone can help. :) Thanks in advance!