Stellar variability refers to the changes in brightness of a star over time. These fluctuations can occur for various reasons, such as the star's internal processes, interactions with other stars, or the presence of orbiting planets. For example, some stars, like Cepheid variables, have regular brightness cycles, while others may change unpredictably. Understanding stellar variability is important for astronomers because it helps them learn more about the life cycles of stars and the structure of our universe. By studying these changes, scientists can also measure distances in space, using methods like standard candles, which rely on the predictable brightness of certain variable stars.