What is the correct order of spectral types from hottest to coolest?
Answer
O, B, A, F, G, K, M
The sequence of spectral types, O, B, A, F, G, K, M, represents a fundamental ordering based directly on the star's surface temperature. The O-type stars are the hottest in this standard sequence, often appearing blue, while the M-type stars are the coolest, appearing distinctly red. This sequence is an established physical scale where decreasing letter designation corresponds to decreasing temperature, meaning O is hottest and M is coolest.
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