Stellar Astronomy: Part 5 – Variable Stars

How do stars change over time?  In parts 3 and 4, we discussed some of the scenarios secular astronomers have proposed for stellar evolution.  These included the now-discredited idea that stars evolve along the main sequence from blue to red, along with modern ideas of giants and supergiants being aged stars.  Unfortunately, such long-term changes cannot be observed and therefore are beyond the scope of operational science.  Nonetheless, some stars change in ways that have been observed in history, and some types of changes are even observable in the present.  In particular, stars can change in luminosity, appearing either brighter or fainter over time.  These are called variable stars.