Messier 43

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 HD 37061 (variable star designation NU Ori), the focus of the H II region, 400 +/- away. This is a triple star system with the brighter component being a single-lined spectroscopic binary. The main component is a blue-white hued B-type main-sequence star with a stellar classification of B0.5V or B1V. It has $19$ times the mass of the Sun and $5.7$ times the Sun's radius. It is radiating over 26,000 times the Sun's luminosity from its photosphere at an effective temperature of 31,000 K. It is spinning rapidly with a projected rotational velocity of around 200 km/s.

The H II region is a roundish volume of ionized hydrogen. It has a diameter of about $4.5 arcminute$, at its distance meaning it measures 0.65 pc. The net (meaning omitting the star) hydrogen alpha luminosity of this region is $3 erg s^{−1}$; equivalent to $78 solar luminosity$. 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.