The H-R diagram is a scatter graph of stars, a plot of stellar absolute magnitude or luminosity versus temperature or stellar classification. It is an important astronomical tool for understanding how stars evolve over time. Stellar evolution cannot... (View More) be studied by observing individual stars as most changes occur over millions and billions of years. Astrophysicists observe numerous stars at various stages in their evolutionary history to determine their changing properties and probable evolutionary tracks across the H-R diagram. In this activity, students plot both maxima and minima with corresponding stellar classifications for several variables, and then identify the type of variability: Cepheid, RR Lyrae, Mira or Semiregular. This activity includes background information, a teacher guide, a student activity, and accompanying worksheets. The American Association of Variable Star Observers (AAVSO) and The Chandra X-Ray mission have collaborated to develop this activity. (View Less)