The Saha equation is a mathematical formula used in astrophysics to describe the ionization of atoms in a gas. It relates the ionization state of a gas to its temperature and pressure, helping scientists understand how many atoms are ionized at a given temperature. This is particularly important in studying stars and other celestial bodies, where high temperatures can lead to significant ionization. Developed by Indian physicist Meghnad Saha in 1920, the equation provides insights into the physical conditions of stellar atmospheres. By applying the Saha equation, researchers can analyze the spectra of stars, revealing information about their composition, temperature, and density.