Ice Diamond Riddle SOLUTION ft. Vsauce's Michael Stevens

For the last riddle. I know that an instrument that shows a star’a spectrum is called a spectrometer. They are used to find the composition of different objects. I’m pretty sure finding temperature with a spectrum uses the H absorption lines. The easy answer to this riddle is just look at the color. Temps low to high; red, orange, yellow, white, and blue. But if you
Couldn’t see the color, then this makes things difficult. I guess you could find the amount of radiation coming from the star, as hotter stars usually fuse faster than cooler stars.