period-luminosity relationship

The period-luminosity relationship is a scientific way to measure the brightness of certain stars, called Cepheid variables. These stars pulse regularly, with their pulsation period (the time it takes to complete a cycle) directly linked to their intrinsic luminosity (actual brightness). By observing the length of their pulsation period, scientists can determine how bright the star truly is. Comparing this with how bright the star appears from Earth allows astronomers to calculate its distance. This relationship is a crucial tool for measuring cosmic scales and understanding the universe's size.