Star groupings on a Power-Temperature or Hertzsprung-Russell Diagram. Each dot represents an individual star. The curved line traces the possible evolutionary sequence of a star, such as the sun, from its condensation out of a dust and gas cloud (birth) to Its period as a main sequence star where it remains a long time before expanding into a red giant followed by contraction, explosion (nova or supernova) and collapse into a white dwarf. A more massive star might collapse further into a neutron star (pulsar) or even a black hole. The bottom scales give the temperature in degrees kelvin, the corresponding colors and the spectral class letters. The circle centered on the sun (embracing F, G and K stars of the Main Sequence) includes the sun-like stars which are regarded as SETI candidates. A typical star, such as the sun, is about a million kilometers in diameter, a white dwarf about ten thousand kilometers in diameter (earth size), a neutron star or pulsar about ten kilometers and a black hole less than one kilometer in diameter.