How is the temperature of a star measured?

As stars are very far away, their temperature cannot be measured directly. Fortunately, the light coming from stars can be analyzed through several scientific instruments. Although all stars appear white, they have different colours when carefully viewed. The variations are a result of their temperature – cold stars appear red, and hot ones blue or white. The colour of a star is measured by an instrument called photoelectric photometer, which involves passing the light through different filters and finding the amount that passes through each filter. The measures from the photometer are converted to temperature, using standard scales.