B

To determine the temperature of stars, astronomers often use Wien's Displacement Law.
Step 1: Wien's Displacement Law states that the wavelength at which the emission of a black body spectrum is maximum is inversely proportional to its temperature.
Step 2: The law can be mathematically expressed as:
$$ \lambda_{max} = \frac{b}{T} $$
where \( \lambda_{max} \) is the peak wavelength, \( b \) is Wien's displacement constant (approximately 2898 µm·K), and \( T \) is the absolute temperature in Kelvin.
Step 3: By observing the spectrum of a star and determining the wavelength of its peak emission, astronomers can use this formula to calculate the star's surface temperature.
Therefore, the correct option is B.