gen-briefly-explain-spectral-classification-of-stars-and-one-com-a0ca

Briefly explain spectral classification of stars and one common misconception about it.

## Spectral Classification of Stars **The System:** Stars are classified by their surface temperature using spectral types: **O, B, A, F, G, K, M** (from hottest to coolest). This sequence is based on the absorption lines visible in each star's spectrum. O-type stars are blue and extremely hot (>30,000 K), while M-type stars are red and cool (~3,000 K). Each class is further divided into subcategories 0-9, with our Sun being a G2 star. **Common Misconception:** Many people think spectral class directly indicates a star's **brightness** or **size**. In reality, it only reveals **surface temperature**. A cool, red M-type star could be either a tiny, dim red dwarf *or* a massive, luminous red supergiant like Betelgeuse. To fully characterize a star, astronomers use the Hertzsprung-Russell diagram, which plots spectral class against luminosity, revealing that stars of the same temperature can vary enormously in size and total energy output. This is why astronomers add luminosity classes (I-V) to spectral types—so "M2 V" indicates a red dwarf, while "M2 I" indicates a red supergiant.