1. Temperature: This is determined by the star's color. Hotter stars emit more blue light, while cooler stars emit more red light. Temperature is often measured in Kelvin (K).
2. Luminosity: This refers to the total amount of energy a star radiates per second. It's essentially how bright a star is, and can be measured in units like Watts or solar luminosities (the luminosity of our Sun).
3. Size: The radius of a star can be determined by measuring its angular size and distance. It's often expressed in terms of solar radii (the radius of our Sun).
4. Chemical Composition: Stars are mostly composed of hydrogen and helium, but they also contain trace amounts of heavier elements. Analyzing the light emitted from a star allows astronomers to determine the proportions of these elements.
These four characteristics are combined to create the Hertzsprung-Russell (H-R) diagram, a powerful tool that helps astronomers understand the life cycle of stars.
