Then bright red as it gets hotter. Then white hot, then blue. The color of light emitted varies with the temperature. Our bodies emit radiation, infrared not visible. This behavior of objects is called Wien's Law .
Hotter bodies radiate more strongly at shorter wavelength.
See figure 3.6 on page 101 . Greek letter, stands for the wavelength at which body most strongly radiates. We can figure out what temperature things are out in space simply from the overall color we see. More accurately, astronomers will send the light through a prism and measure how much radiation there is at each wavelength. The object's temperature is found from where the peak wavelength occurs.