Find the Sun's Surface Temperature from its Thermal Radiation Spectrum E. Figure 4 below is the thermal radiation spectrum of our Sun. Determine the peak wavelength by finding the highest point the blue line reaches and then trace it down to the x-axis. This is best done by placing your ruler parallel to the y-axis and lining it up at the peak of the blue line. Then to find the wavelength value, find the place the ruler intersects with it on the x-axis. This will be your value for 2max. Record this value for question 13. Then use the Wein's Law below to find the surface temperature (T) of the Sun in Kelvin and answer question 14. Wien's Law 2.9 x 106 nm/K T = Amax Here T is in Kelvin (K) and Amax is in nanometers (nm). 13. Amax = nm 14. T = K