The most common way to classify a star is by which property?

• A. The color of light it emits
• B. The star's distance from Earth
• C. The star's age
• D. The star's rotational velocity

Answer: (A)

Color of the light a star emits is the main way we classify stars because it directly reflects the star’s surface temperature. Hotter stars shine more blue-white, while cooler ones glow red, and this color difference maps to a sequence of spectral types. The spectrum also shows absorption lines that depend on temperature and chemical makeup, reinforcing the temperature-based grouping.

Distance doesn’t change a star’s color or temperature, it only affects how bright it appears from Earth, so it isn’t used for the basic classification. Age and rotational velocity are real properties but don’t define broad, standard categories in the same way color/temperature does; stars of many ages can share the same color, and rotation varies within those categories.