What are reference lines?
Reference lines are the characteric pattern of absorption or emission lines for a substance which is at rest with respect to the observer. Reference lines for a particular substance can be measured in the laboratory. If the photons are jumping up and down, both in different objects, won’t emission and absorption lines complement each other to form a full spectrum? In which case how can we find the Sun’s, etc.’s characteristics? No, not necessarily- there can be net emission or absorption of light at particular frequencies. For the case of emission lines, energy can be transferred to electrons and bump them up into higher energy levels by some means other than absorption of light. For instance, collisions between atoms in a hot gas can transfer energy to electrons and put them in excited states. Then electrons drop back down to lower levels via emission of photons. So they go up by collisions, down by emission of light, and there’s a net emission of light at the frequencies correspondin
