Orion nebula. Optical image of the Orion nebula (red) containing two bright patches. The larger patch (M42, NGC 1976) has a smaller neighbour (M43, NGC 1982). The associated reflection nebula (NGC 1977, blue) is at upper left. These nebulae lie around 1500 light years away in the constellation Orion. M42 and M43 are HII regions, areas of gas (mainly hydrogen) and dust where newly-born stars, including the three stars of the Trapezium, excite the gas and cause it to glow. NGC 1977 is visible only because it reflects light from nearby stars. North is at top.