H-alpha is a specific wavelength of light emitted by hydrogen atoms when an electron transitions from the third energy level to the second. This light is part of the hydrogen emission spectrum and is commonly observed in astrophysics, particularly in the study of stars and nebulae. Astronomers use H-alpha filters to observe solar phenomena, such as solar flares and prominences, as well as to study the formation of stars in nebulae. The H-alpha line is crucial for understanding the dynamics and composition of various celestial objects.