Spectral class

Definition

A spectral class is a classification of stars based on their spectral characteristics, particularly the absorption lines present in their spectra. These classes are primarily determined by a star's surface temperature and are categorized using the letters O, B, A, F, G, K, and M.

5 Must Know Facts For Your Next Test

1. Spectral classes range from hot to cool stars: O (hottest), B, A, F, G, K, M (coolest).
2. Each spectral class is further divided into subclasses numbered from 0 to 9.
3. O-type stars are blue and have temperatures above 30,000 Kelvin.
4. G-type stars include our Sun and have temperatures between 5,300 and 6,000 Kelvin.
5. M-type stars are red and have temperatures below 3,500 Kelvin.

Review Questions

• What letter represents the hottest spectral class?
• Which spectral class does the Sun belong to?
• How are spectral classes subdivided?

Related terms

Hertzsprung-Russell Diagram: A graphical tool that plots stars according to their luminosity and temperature or spectral class.

Absorption Lines:

Dark lines in a star's spectrum caused by specific elements absorbing particular wavelengths of light.

Brown Dwarf:

Substellar objects that are cooler than the smallest main-sequence stars and often classified under L or T spectral classes.