Messier 43

NOTOC 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 (Messier 42), 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.

The main ionizing star in this nebula is the quadruple star system NU Orionis (HD 37061), the focus of the H II region, 1360 ± away.

The H II region is a roundish volume of ionized hydrogen. It has a diameter of about , at its distance meaning it measures 0.65 pc. The net (meaning omitting the star) hydrogen alpha luminosity of this region is ; equivalent to . There is a dark lane crossing the whole west-centre strip from north to south, known as the M43 dark lane, which forming a swirling belt extension to the south links to Orion's northeast dark lane. All of these resemble a mixture of smoke rising from a chimney and in watercolour broad and fine dark brushstrokes, at many wavelengths.