• Wien’s displacement law relates the observed wavelength of light from an object to its surface temperature, it states:

The black body radiation curve for different temperatures peaks at a wavelength that is inversely proportional to the temperature

• This relation can be written as:

• λmax?is the maximum wavelength (m) emitted by an object at the peak intensity
• T?is the surface temperature (K) of an object

• Wien's Law equation is given by:

λmaxT = 2.9 × 10?3?m K

• This equation tells us the higher the temperature of a body:
  • The shorter the wavelength at the peak intensity, so?hotter?objects tend to be?white or blue,?and?cooler?objects tend to be?red or yellow
  • The greater the intensity of the radiation at each wavelength

   

Table to compare surface temperature and star colour

Step 1:?Write down Wien’s displacement law

λmaxT = 2.9 × 10-3?m K

Step 2:?Rearrange for temperature T

Step 3:?Calculate the surface temperature of each star

Step 4:?Write a concluding sentence

Betelgeuse has a surface temperature of 3500 K, therefore, it is much cooler than Rigel

The Orion Constellation; cooler stars, such as Betelguese, appear red or yellow, while hotter stars, such as Rigel, appear white or blue