Classification of stars - temperature and black body radiation

A-level AQA physics options astrophysics. CH2

Observations made from the black body curve graph

• stars emit all wavelengths of light

• Each curve on the graph shows the distribution of the energy radiated across the spectrum (of wavelengths) for a star of a specific temperature

• The intensity is inversely proportional to the peak wavelength

• The temperature is inversely proportional to the peak wavelength

• The peak is displaced to the left (smaller wavelength) as the temperature increases (Wien’s displacement law)

How can we understand the chemical composition of stars?

• through observing their absorption spectra

• dense, hot matter (core of star) emits electromagnetic waves

• EM waves reach the gaseous layers of stars (in the outer atmosphere)

• This gas absorbs the EM waves whose photons excite the electrons in the gas, which emit photons in all directions when de-excite

• When the EM waves reach us, these missing wavelengths result in absorption spectra.

Three types of line spectra

• continuous

• emission

• absorption

What is the continuous spectrum?

• spectrum on which all wavelengths of light are emitted

• a broad range of colours (depending on a star's temperature)

• Produced by hot, dense sources, such as the cores of stars