Famous Stars, Part I -15 107 Hypergiants 106 -10 105 Supergiants Supe -5 ai n qu en 103 Giants 100 10 bgiants Sub Subgiants ce Dwarfs Luminosity ys tri p M se Bright Brig giants Red giant branch Ins ta bil it 0 1 5 M ai n se qu .010 en ce Subdwarfs .001 10 10-3 White dwarfs 10-4 15 10-5 Brown dwarfs 20 O B A F G K M L T Spectral class p LIFE OF A STAR The Hertzsprung-Russell diagram plots stars according to their spectral class (related to color and temperature) and absolute magnitude (related to luminosity). Stars' locations depend on their mass and age, and they move across the H-R diagram as they evolve. Stars can experience one or more unstable periods, marked by the instability strip. The black line shows the approximate path a 5-solar-mass star will take across the diagram. When it enters the correct part of the strip, it becomes a Cepheid. (A star's behavior in the strip depends on its mass; the final crossing as the star dies won't create Cepheid pulsations.) The gray labels are luminosity classes (see S&T: Dec. 2018, p. 27) and their boundaries here are rough. 18 M A RCH 2 019 * SK Y & TELESCOPE S&T ILLUSTR ATION, H-R DIAG R A M SOURCE: RURSUS / WIK IMEDIA COMMONS / CC BY-SA 3.0, STAR TR ACK SOURCE: LITHOPSIAN / WIKIMEDIA COMMONS / CC BY-SA 4.0 Absolute magnitude 104 Asymptotic giant branch