I posted this http://answers.yahoo.com/question/i...GXejba9DH1G;_ylv=3?qid=20110618143816AAgRMyF"on Yahoo Answers yesterday, but it might be too specialized: If I understand correctly, the Cosmic Microwave Background Radiation is a perfect thermal (black-body) spectrum. But stars have an absorption spectrum that can be used to find out what kinds of elements are in them. In general can the spectral lines be used to calibrate, then compared to the thermal spectrum to find out how hot a star is? (I guess that's a second question.) Is that a technique in common use? Main question is still: Does the CMBR have a detectable absorption spectrum?