Lyman-alpha nebulae are large, diffuse clouds of gas that emit Lyman-alpha radiation, a particular wavelength of ultraviolet light. These nebulae are typically found in the early universe and are believed to be important in understanding the formation and evolution of galaxies. They are often associated with regions of intense star formation and are thought to be powered by the intense radiation emitted by young, massive stars. Lyman-alpha nebulae can provide valuable insights into the processes of galaxy formation and the enrichment of the interstellar medium with heavy elements. Studies of Lyman-alpha nebulae can also help astronomers understand the conditions in the early universe and the role of gas in the formation and evolution of galaxies.