Final answer:
Scientists use methods such as stellar census, analyzing characteristics, and indirect testing to learn about star ages.
Step-by-step explanation:
Astronomers cannot observe a star pass through each of its stages of life or even one stage of its life because stars live much longer than human lifetimes. Scientists use methods such as stellar census, analyzing characteristics, and indirect testing to learn about star ages. However, scientists have developed methods to learn about star ages through a combination of observation and theory.
These methods include conducting a stellar census to measure the characteristics of many stars, analyzing the differences in characteristics such as mass, temperature, and luminosity, and using indirect testing and calculations based on the messages contained in the light and radiation emitted by stars.