gen-define-spectral-classification-of-stars-and-give-one-short-w-7437

Define spectral classification of stars and give one short worked example.

# Spectral Classification of Stars ## Definition **Spectral classification** is a system for categorizing stars based on their **surface temperature** as revealed by their **absorption line spectra**. Stars are classified using letter types that form a temperature sequence. ### The Main Sequence (hottest to coolest): **O - B - A - F - G - K - M** (Mnemonic: "Oh Be A Fine Girl/Guy Kiss Me") Each class is subdivided into 10 subclasses (0-9), where 0 is hotter and 9 is cooler within that class. ### Key Characteristics: - **O stars**: Blue, very hot (>30,000 K), ionized helium lines - **B stars**: Blue-white, hot (10,000-30,000 K), neutral helium lines - **A stars**: White (7,500-10,000 K), strong hydrogen lines - **F stars**: Yellow-white (6,000-7,500 K), ionized calcium lines - **G stars**: Yellow (5,200-6,000 K), ionized calcium, weak hydrogen - **K stars**: Orange (3,700-5,200 K), neutral metal lines - **M stars**: Red, cool (<3,700 K), molecular bands (TiO) ## Worked Example **Star: The Sun** **Observations:** - Surface temperature: ~5,778 K - Spectrum shows: Strong ionized calcium (Ca II) H and K lines, moderate hydrogen lines, presence of neutral metal lines **Classification:** The temperature places it in the **G class** (5,200-6,000 K). The specific spectral features indicate it's near the middle of this range. **Result: G2V** - **G2** = spectral type and subclass - **V** = luminosity class (main sequence dwarf star)