Transcript: The spectrum of the Sun tells us important things about the atmosphere of the Sun. Two of Kirchhoff’s laws are involved. First, a sufficiently hot gas will emit a thermal spectrum whose radiation peaks in the visible part of the spectrum. This is what we see for sunlight, and the wavelength of the peak of the emission is a clue that the temperature of the atmosphere, or edge of the Sun, is about 5,700 degrees Kelvin. The fact that the Sun’s spectrum is crossed by narrow absorption lines means, by Kirchhoff’s law, that the interior gas must have a cooler outer layer. Thus, the 5,700 degree gas at the outer edge of the Sun lies outside gas that must be hotter yet. The Sun gets hotter as we go deeper inside it.