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M43 is a HII region located in the constellation of Orion that was discovered by Jean-Jacques Dortous de Mairan sometime before 1731. As part of the famous Orion Nebula (M42), it's positioned just north of the main nebula and separated from it by a narrow dust lane. With an apparent mag. of +9.0, M43 is about 100 times fainter than M42, but still bright enough to be seen with binoculars.

Occasionally, ninth mag. nebulae like M43 can be difficult to find - especially if located in barren parts of the sky - but not this one. Firstly, it's located in majestic Orion, perhaps the most recognizable of all constellations, secondly it's part of the Orion Nebula and therefore positioned right next to the great showpiece object and finally it has a relatively high surface brightness. Of course, finding M42 is easy, it's positioned 5 degrees south of the three bright stars that form Orion's belt (Mintaka, Alnilam and Alnitak). M43 is located just 8 arc minutes north of M42 surrounding a 7th magnitude star. M43 (and M42) are best seen during the months of December, January and February.

M43 De Mairan's Nebula (credit:- NASA, ESA, and The Hubble Heritage Team (STScI/AURA))

Finder Chart for M43 (credit:- freestarcharts)

Finder Chart for M43 - pdf format (credit:- freestarcharts)

In 10x50 binoculars, M43 appears as a small, faint fuzzy elongated patch with a noticeably brighter centre. NU Orionis, the irregular young star at the heart of M43, is easily visible in binoculars. This star excites the surrounding gas causing the nebula to shine and varies in brightness between magnitudes +6.5 and +7.6.

M43 is a nice sight in larger 20x80 binoculars, with the nebula appearing defined and looking somewhat comma shaped. Through a 100mm (4-inch) telescope, the centre star appears bright. M43 doesn't show as much range in brightness or detail as M42, but it has a bright ring around the star, which in turn is surrounded by the fainter comma shaped nebulosity. The dark lane separating M43 from the gigantic Orion Nebula is easily visible. Larger telescopes of the order 200mm (8-inch) reveal subtle details such as tendrils, smoky wisps and dark and light areas spread across the surface of M43, particularly along the eastern side.

M43 is 1,600 light-years from Earth and has an apparent size of 20 x 15 arc minutes, which corresponds to a spatial diameter of 9 light-years. Physically, M43 is a part of the Orion Nebula and both M42 and M43 are part of the much larger Orion Molecular Cloud Complex.

Historically, when the first photograph of the Orion Nebula was made by Henry Draper on March 14, 1882, M43 was also visible.

M43 Data Table

NameDe Mairan's Nebula
Object TypeHII region
Distance (light-years)1,600
Apparent Mag.+9.0
RA (J2000)05h 35m 31s
DEC (J2000)-05d 16m 03s
Apparent Size (arc mins)20 x 15
Radius (light-years)4.5
Notable FeaturePart of the Orion Nebula