- In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the rainbow of colors interspersed with spectral lines. Each line indicates a particular chemical element or molecule, with the line strength indicating the abundance of that element. The strengths of the different spectral lines vary mainly due to the temperature of the photosphere, although in some cases there are true abundance differences. The spectral class of a star is a short code primarily summarizing the ionization state, giving an objective measure of the photosphere’s temperature.
- Bertrand Russell (plato.standford.edu)
Bertrand Arthur William Russell (1872–1970) was a British philosopher, logician, essayist and social critic best known for his work in mathematical logic and analytic philosophy. His most influential contributions include his championing of logicism (the view that mathematics is in some important sense reducible to logic), his refining of Gottlob Frege’s predicate calculus (which still forms the basis of most contemporary systems of logic), his defense of neutral monism (the view that the world consists of just one type of substance which is neither exclusively mental nor exclusively physical), and his theories of definite descriptions, logical atomism and logical types.