Spectrum obtained using the 74 inch telescope at Mt Stromlo. Pictured above is a series of spectra from average stars of different spectral classes. The darker lines are the wavelengths at which certain particles in the atmosphere of the star absorb some of the light of the star, leaving dark lines. It is from these "absorbsion lines" that we can discover what substances are contained in the atmosphere in the star. If a substance absorbs light at a certain frequency, it also emits light at that frequency. Therefore we can discover atoms in a star's atmosphere by looking at "emmision spectra" and comparing it to the absorbed wavelengths. Superimposed on the above image is one of the average spectra for a B class star. You can see the black lines corresponding with the dips in the absorbsion spectra. The most promenent dips are the Hydrogen Balmer series. This series is caused by the electrons in a hydrogen atom's shell moving between different energy levels as they absorb energy from the light. Because Regulus is a hot blue star, we would not expect to see much more than hydrogen absorbsion spectra. There is a small helium absorbsion line at the red end of the spectrum though. The reason for this is because in such a hot star the many violent collisions breaks up molecules and strips most atoms of their electrons. Only strong atoms like hydrogen can survive. Another important thing we can learn from the spectrum of a star is it's temperature. We can do this because of black body radiation. When things heat up they glow, first red and then blue through to white. All substances do this in the same way. When the objects are heated up enough, all of their spectrum curves look the same. This is called black body radiation. We take a black body spectrum for a certain temperature and match it up with the spectrum of a star. If it matches then the temperature of the star must be approximatly the same as the temperature of the black body. Created by Joseph Curtis on 29/05/02 Page was last updated on: