Measuring extremely high/low temperatures

I understand that the range of extreme temperature is from 0-15million K. What are the ways that we can measure this? How did they figure out the temperature of the sun?

thermocouple thermometer? blackbody radiation? optical pyrometer? I've tried searching for general information on these online but they usually take me to pages that sell thermometers and pyrometers.

I just registered because I'm taking an introductory online physics course where I have to teach myself basically. This looks like a great site which I will be reading very often to help myself get through physics. I'm pretty intimidated by this subject (and this forum!) because I have never taken a physics class and I'm having some issues already so any help would be greatly appreciated.

Thanks
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 Recognitions: Homework Help While the lowest possible temperature is absolute zero, I do not know of any existing upper temperature limit. Temperature is the average kinetic energy of the atoms/molecules making up whatever it is you're taking the temperature of after all. But physically speaking, there may be a limit where the energy is so high matter cannot exist as we know it (i.e. atoms). This is probably not the only way, but the temperature of sun can be calculated by simply looking at its emission spectrum. Planck's Law for black body radiation should have the math needed. It says that any black body at any temperature will have a maximum emission at a specific wavelength. This wavelength gets smaller as the temperature increases. And if I have my facts right, the sun radiates most of its energy in the visible spectrum, peaking at around the green band.
 For temperatures approaching 0K, they use a Bose statistic which measures temperature based on the number of atoms in the ground state.

Measuring extremely high/low temperatures

thank you, i appreciate it