Messier 43 or M43, also known as De Mairan's Nebula and NGC 1982, is a star-forming nebula with a prominent H II region in the equatorial constellation of Orion. It was discovered by the French scientist Jean-Jacques d'Ortous de Mairan some time before 1731, then catalogued by Charles Messier in 1769. It is physically part of the Orion Nebula, separate from that main nebula by a dense lane of dust known as the northeast dark lane. It is part of the much larger Orion molecular cloud complex.

Orion is a constellation which is visible from most parts of the world. As well as being one of the 88 modern constellations, it was one of the 48 constellations listed by the 2nd-century astronomer Ptolemy. It is named for a hunter in Greek mythology.