M43 — De Mairan's Nebula

About

De Mairan's Nebula, a roundish HII region about 1,300 light-years away, physically part of the Orion Nebula but split from M42 by a dark dust lane. It is ionised by NU Orionis, a quadruple star system.

Imaging tips

• About 20′ × 15′: 1,210–2,020 mm on APS-C spans a third to half of the frame, while M42 sits 8′ away, so a wider frame holds both.
• The brightness range is large: one imager used 30–60 s subs for the bright core and 30-minute subs for the dust, and called it the hardest object he had processed.
• Hα is the grounded narrowband choice, since NU Orionis is too cool for much OIII. One imager still shot Hα plus OIII and added RGB for the reflection nebulosity.
• Faint overall at 23.8 mag/arcsec², so plan long integration. Best in December.