Question: how hot is the sun

Philip Ratcliffe answered on 11 Nov 2014:

Well, that’s something I actually teach in one of my courses: at the surface the temperature is about 5,778 K (which is pretty hot), but in the middle (the core) it’s around 15.7 million K (much much hotter).
Now of course, you could’ve easily got that from Wikipedia, the more interesting question would’ve been, how do we measure it?
Well, we can’t get near enough to use anything like a normal thermometer, but we can use what know about other hot things. We know that hot objects radiate light and the colour or rather range and intensities of the different wavelengths (what we technically call the spectrum) vary rather precisely according to the temperature. So from what we “see” (not only with our eyes but also with instruments sensitive to other wavelengths), we can estimate quite well the temperature at the surface, which is the bit we see.
The problem remains of the inside or core temperature – this is much tougher and requires all our knowledge about how the Sun works (thermonuclear fusion) and the temperature required to do what it does.