Kirchhoff’s Laws of Radiation
•Relate continuous spectra, emission line spectra, &
•                       absorption line spectra
1.Hot opaque solid (dense gas) emits light of all wavelengths ® continuous spectrum of radiation
2.Low density (transparent) hot gas emits spectrum of bright emission lines
3.Low density (transparent) cool gas in front of  a blackbody absorbs wavelengths from the  continuous spectrum ® dark absorption line spectrum on continuous spectrum (wavelengths same as emission lines from hot gas)
•Spectroscopy enables determinations of chemical structure of stars
1.