Messier 42, M42, or NGC 1976 is a diffuse nebula situated south of Orion's Belt. One of the brightest nebulae and is visible to the naked eye in the night sky. It is located 1,344 light years away and is the closest region of massive star formation in outer space to Earth. It is seen as the middle star in the sword of Orion, which are the three stars located south of Orion's Belt. The nebula has revealed much about the process of how stars and planetary systems are formed from collapsing clouds of gas and dust. Astronomers have directly observed protoplanetary disks, brown dwarfs, intense and turbulent motions of the gas, and the photo-ionizing effects of massive nearby stars in the nebula.