M43 - De Mairan´s Nebula

Messier 43 or M43 (also designated NGC 1982) is a nebula in the constellation Orion. It has an apparent visual magnitude of 9 and its angular diameter is 20x15 arc-minutes. M43 lies at an estimated distance of 1600 light years. The Equinox 2000 coordinates are RA= 5h 35.6m, Dec= -05° 16´ which makes M43 best seen during the winter. The Messier Winter Star Chart shows the position of all Messier objects visible during that season. As one of the more famous objects in the Messier Catalog, it is commonly known as the De Mairan´s Nebula.

The teardrop shaped De Mairan's Nebula is physically part of the much larger Great Nebula in Orion (M42) although it appears separated by a dark dust lane in the foreground. The entire area is a complex region of active star formation where some of the hotest and brightest stars are coalescing. Composed of glowing gas and dark dust, M43 and M42 are part of the Orion Molecular Cloud Complex. This huge region also includes the Horsehead Nebula located south of Zeta Orionis (Alnitak), the easternmost star in the Belt of Orion.

The red glow visible in M43 is characteristic of ionized hydrogen as it recombines with lost electrons. De Mairan's Nebula lies in the Orion Arm of the Milky Way Galaxy at a distance of about 1300 light years.

The blue nebula north of M43 is an interstellar cloud of dust reflecting light from hot young stars. It is composed of three regions known as NGC 1977, NGC 1975, and NGC 1973. Physically associated with the Great Nebula, it lies at about the same distance.

The image above shows the uncropped view of M43 (and M42) through the Takahashi E-180 Astrograph (North is up). A 3x enlargement of this image appears to the right.

In spite of its inclusion in the Messier Catalog, this diffuse nebula was actually discovered by J-J. de Mairan in 1744. According to Kharchenko et al. (2005), the distance of M43 is 1300 light years and its diameter is 3 light years.

For more information, see the Messier Catalog as well as specific entries for M43 in Wikipedia and SEDS.

Messier's Description of M43

March 4, 1769
`Position of the little star surrounded by nebulosity and which is below the nebula of the sword of Orion. M. Messier has included it in the drawing of the Great [Nebula].'

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