Barnard's Loop is a large, bright arc of emission nebula located in the constellation Orion. It is part of a complex of interstellar gas and dust, surrounding the famous Orion Nebula. This loop is approximately 1,500 light-years away from Earth and spans about 300 light-years in diameter. The loop is named after the American astronomer Edward Emerson Barnard, who first cataloged it in the early 20th century. It is primarily composed of hydrogen gas, which glows due to the ionization caused by nearby hot stars. Observing Barnard's Loop helps astronomers study the processes of star formation and the structure of our galaxy.