I would like some help understanding absorption spectra, for example, by a cloud of gas in space. Photons might be absorbed if their energy matches a transition in one of the atoms or molecules in the gas. I am happy with that part but surely the atoms or molecules drop back to their ground state at some point and emit another photon of the same energy. So, does not the gas reach a steady state with no net absorption? I have done some reading and I think that I found that the answer is as simple as the emitted photon may be in a different direction.
If I have not gone wrong so far then please confirm or correct this thought experiment.
An object is detected in space emitting a beam of light. This is analysed and found to be a pure black body spectrum with no absorption lines.
Three space stations A, B, and C are set up. Initially, they are in line and within the beam. A is nearest and C is furthest. They all observe the same spectrum (maybe slightly weaker for B and C if the beam spreads a bit).
Station B is moved perpendicularly to the line between them out of the beam. So, now B cannot observe the beam.
A cloud of gas floats to where B was. A observes no change. C observes an spectrum with absorption lines caused by the cloud. B now sees a faint glow from the cloud as some of the re-emitted photons are in its direction.
Clarification on point 4. I don't mean that only station B sees the glow from the cloud. I expect that it goes in all directions. This is why I said "faint glow", station B just gets a small portion of it. "A observes no change" - well if it looked in the other direction then it should also see the glow.
Edit: correction made in 4.