H-alpha emission is a type of emission line in the spectrum of hydrogen that falls within the visible light range at a wavelength of 656.28 nanometers. This spectral line is produced when an electron transitions from the third energy level to the second energy level in a hydrogen atom. H-alpha emission is commonly used in astronomy to study the properties of celestial objects such as stars, galaxies, and nebulae. Researchers use H-alpha emission to determine the temperature, density, and velocity of objects in space, as well as to study the distribution of ionized gas in the interstellar medium.