Stellar Spectral Classes
Physics: AQA A Level, topic 9.2.4
Stellar Spectra
A lot can be learned from stellar spectra, such as their temperature and composition.
Temperature sensitive
- The temperature of the star has an effect on the absorption of light by atoms.
- The hydrogen Balmer lines (which occur when the electron drops down to the n = 2 state) are strongly temperature sensitive as shown in the diagram.
Energy levels
- Cool stars have very few hydrogen atoms in the n = 2 level and so give weak Balmer lines.
- Very hot stars have more atoms in the n = 3 level.
- ‘A’ class stars have the right temperature for most of the electrons to be in the n = 2 level.
Test yourself on Stellar Spectral Classes
What type of stars produce the strongest Balmer lines?
Which of these statements are true about stellar spectral classes?