In one of the standard candle methodologies, it is given in my book that by looking at the EM spectrum , we can know the temp. of the star by wien's law... To this point, everything's fine... now, the next sentence is FROM THE WIDTH OF THE SPECTRAL LINES, YOU CAN DETERMINE WHETHER OR NOT IT IS A MAIN SEQUENCE STAR... This part is completely confusing.. I understand nothing and don't know what do they mean by this. What is the width of spectral line. DO they mean the absobtion lines and how would that determine whether it is a main sequence star or NOT??? I really need help, so whoever can contribute with a fine answer, i am so thankful to him/her. Thanks!