The spectral classes are an important tool in stellar classification. Stars are distinguished by their temperatures and colors. Astrophysicists classify stars according to 7 main spectral classes (0 - blue, B - bluish-white, A - white, F - white-yellow, G - yellow, K - orange, M - red).
The temperature of the stars decreases from blue (very hot) to red (less hot). The hotter a star,
the brighter its surface.