1. Temperature: Measured in Kelvin (K) and determined by the star's color. Hotter stars appear blue, while cooler stars appear red.
2. Luminosity: The amount of energy a star emits per second, measured in Watts or solar luminosities (the Sun's luminosity).
3. Size: The radius of the star, determined by its temperature and luminosity.
4. Mass: The amount of matter in a star, measured in solar masses (the Sun's mass).
5. Composition: The chemical makeup of a star, primarily hydrogen and helium, but also containing trace amounts of other elements.
6. Age: How long a star has been shining, measured in years.
7. Evolutionary Stage: The current stage in a star's life cycle, such as main sequence, red giant, white dwarf, etc.
While the first four variables are used to create the Hertzsprung-Russell diagram (H-R diagram), which is a fundamental tool for understanding stellar evolution, the other three variables are also essential for a complete classification of stars.
