Using Radiation to Investigate Stars

2.5.1 Stellar Spectrum
A stellar spectrum consists of a continuous emission spectrum coming from the dense gas of the surface of the star, and a line absorption spectrum which arises due to electromagnetic radiation emitted through the tenuous atmosphere of the star.
2.5.2 Black Bodies
Bodies which absorb all incident radiation are known as black bodies. Black bodies also emit energy in all regions of the electromagnetic spectrum, which is why stars are good approximations to black bodies. Wien’s displacement law states that the wavelength distribution of thermal radiation form a black body is essentially the same except that each wavelength is displace on the graph, which means that the peak wavelength (λmax) is proportional (with constant of proportionality Wein’s displacement constant, b) to the inverse of the absolute temperature (T), and this is converted to the follow equation:


2.5.3 Stellar Line Spectra

Stellar line spectra analysis has revealed that ∼ 75% of the universe, by mass, is Hydrogen, ∼ 24% of the universe is Helium, the rest is very small quantities of other elements.
2.5.4 Energy Production in Stars
The main energy production mechanism in stars is the proton-proton chain reaction which is a fusion reaction in stars which converts hydrogen to helium. We know about this reaction because we can detect neutrinos, from the rst step of the reaction, on Earth. Here is the reaction: