Stars appear to be white to the naked eye because they emit a mixture of all colors of light However when photographed stars show a range of colors due to their different surface temperatures The coolest stars emit primarily red light while hotter stars emit more blue light This is because hotter stars emit more energy and this energy is released in the form of shorter wavelengths of light such as blue and violet The color of a star can be determined by measuring its spectrum which is the distribution of light that it emits across different wavelengths The wavelength at which the intensity of light reaches a maximum is called the peak wavelength Wien s Law relates the peak wavelength of a star to its surface temperature Surface Temperature 2 98 10 6 K Peak Wavelength nm Where the peak wavelength is measured in nanometers nm and the temperature is measured in Kelvin K For example the Sun has a peak wavelength of about 500 nm Using Wien s Law we can calculate that its surface temperature is about 5800 K The following table shows the relationship between star color and surface temperature Color Red Orange Yellow White Blue Surface Temperature K 3000 3000 5000 5000 6000 6000 7500 7500 Export to Sheets Astronomers use the color of stars to classify them into different types The most common classification scheme is the Morgan Keenan system which divides stars into seven spectral classes denoted by the letters O