I recently attended a talk about molecular clouds discussing CO transitions in them. I've been trying to understand spectroscopy in astronomy and have tried reading lots of articles online although I still don't quite get everything. It seems that telescopes can find the intensity emitted by certain sources at different wavelengths, such as in normal spectroscopy, correct? How exactly then can a telescope focus on one particular molecular cloud light years away without having this data obfuscated by all the other interacting objects and interfering waves in space? How are we confident this information came from that particular molecular cloud specifically (is it some sort of filter done against the background? If so, could you explain this)? Also, I saw a temperature vs velocity graph that displayed different CO transitions, but how can such a graph even be constructed? I unfortunately don't have the slides for reference, but I'm just fascinated and slightly confused by how we actually get all this data from telescopes. Any information you have would be great!