Stars whose temperature/luminosity characteristics generally fall along a line from the upper-left corner to the lower-right corner on a Hertzsprung-Russell diagram are called what?

• A. Main sequence stars
• B. Giant stars
• C. White dwarfs
• D. Red supergiants

Answer: (A)

Stars along that diagonal line are in the main sequence, where hydrogen fusion occurs in their cores and the star maintains a stable balance between gravity and pressure. Their temperatures and luminosities are closely tied to mass: more massive stars are hotter and far brighter, placing them toward the upper-left, while less massive stars are cooler and dimmer, landing toward the lower-right. This creates a continuous diagonal band on the Hertzsprung-Russell diagram. Giants and red supergiants sit above-right—bright but cooler—while white dwarfs are hot but faint, in the lower-left. The Sun sits near the middle of this band as a typical mid-mass main-sequence star.