Stellar Astronomy: Part 4 – Of Dwarfs and Supergiants

It is rather amazing what we can know about stars simply by analyzing their light and with rigorous application of logic and mathematics.  We can measure the distance to any nearby star using parallax.  And by multiplying a star’s apparent brightness by the square of its distance, we can determine its actual luminosity.  Furthermore, we can know both the composition and the surface temperature of a star by analyzing the absorption lines of its starlight using a spectroscope.  This led to the field of stellar classification and the discovery of the main sequence.  But why does this sequence exist?  Why are blue main sequence stars so much brighter than red main sequence stars?

Stellar Astronomy: Part 3 – Classes and the Main Sequence

With the technology available in the nineteenth and twentieth centuries, astronomers made a number of wonderful discoveries about the nature of stars.  These included knowledge of the true luminosity of stars as well as their chemical composition and temperature.  Although all stars have a similar chemical composition, they come in a wide variety of luminosities and temperatures.  As more stars were catalogued, astronomers began to notice a pattern.  Secular, evolutionary thinking led to some false interpretations about the cause of this pattern.  This lesson in history is an important one for us today.