What classification letter corresponds to the hottest stars?

The classification letter that corresponds to the hottest stars is "O." In the stellar classification system, stars are categorized into several spectral types based on their temperatures and other characteristics. The spectral types, from hottest to coolest, are O, B, A, F, G, K, and M.

Stars in the O classification are the hottest, with surface temperatures exceeding 30,000 Kelvin. These stars emit a significant amount of their energy in ultraviolet light and are often very luminous. They are typically massive and have short lifespans compared to cooler stars.

As for the other classification letters, M stars, for instance, are among the coolest, with surface temperatures below 3,500 Kelvin. G stars, like our Sun, have temperatures between 5,300 and 6,000 Kelvin. A stars have temperatures in the range of approximately 7,500 to 10,000 Kelvin. Thus, O stars are distinctly hotter than all these other categories, solidifying O as the correct choice for the hottest stars.