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How to Calculate the Average Surface Temperature of the Sun

The sun, like all stars, primarily behaves as what's called a "blackbody." A blackbody is an object that absorbs all the electromagnetic energy that hits it, then redistributes it and emits its own light. A blade of grass, for example, looks green because it reflects some of the light that hits it. A blackbody looks black because it doesn't reflect any light. But that doesn't mean it doesn't emit its own radiation -- in visible light or at infrared wavelengths. It does, and the spectrum of that radiation depends only on its temperature.

Instructions

- 1
  Look up the peak wavelength of solar radiation. You'll find it to be about 550 nanometers, which is 550 x 10^-9 meters, or 550 billionths of a meter.
- 2
  Find Wien's displacement law. This is an expression that correlates the peak wavelength of a blackbody with its temperature. Wien's displacement law shows that the temperature (in kelvins) is 2.898 x 10^-3 divided by the wavelength in meters.
- 3
  Calculate the temperature via Wien's law:
  
  Temperature = 2.898 x 10^-3 / 550 x 10^-9 = 5,269 kelvins.
- 4
  Convert the temperature to whichever scale you find convenient. To change kelvins to degrees Celsius, use this equation:
  
  degrees Celsius = kelvins - 273.
  
  So the temperature of the sun's surface is 4,996 C. You can convert that to degrees Fahrenheit with this formula:
  
  Fahrenheit = (1.8 x degrees Celsius) + 32.
  
  This means the surface of the sun is about 9,025 F.

Astronomy