The behavior of absorption lines and the continuum radiation is also examined. Background and Theory Classification lies at the foundation of nearly every science. We are all aware that biologists classify plants and animals into subgroups called genus and species. Geologists also have an elaborate system of classification for rocks and minerals. Scientists develop classification systems based upon perceived patterns in and relationships among natural objects.
Astronomers are no exception.
They classify planets as terrestrial or Jovian, galaxies as spiral, elliptical or irregular, and stars according to the appearance of their spectra. In this exercise, you will study the method that astronomers use to classify stars, which is called the MK spectral classification system, after the founders, W. W. Morgan and P. C. Keenan. A spectrum of a star is composed of its continuum emission as well as a number of 'lines' which can be either emission or absorption lines. The continuum emission is a product of the blackbody radiation at specific frequencies, caused by electrons in atoms dropping down into lower energy levels. They can also be caused by molecular transitions to lower energy levels.