The Horse Head & Flame Nebulas
18 x 600 seconds at ISO 1600. Astrodon 5nm Ha filter.
The Horsehead Nebula, also known as Barnard 33, is a small dark nebula silhouetted against the glow of the emission nebula IC 434.
This narrow patch of nebulosity extends a degree south of the bright star Zeta Orionis (Alnitak), the leftmost star in Orion's Belt.
Barnard 33 is the most interesting feature of a huge region of gas and dust situated 1,600 light years away in the constellation Orion. It is a dark globule of dust and non-luminous gas, obscuring the light coming from the moderately bright nebula IC 434 behind it. The glow of IC 434 originates from ionized hydrogen gas. The underside of the "neck" of the Horsehead is especially dark, and actually casts a shadow on the field below the "muzzle". The entire region is illuminated by the bright OB star Sigma Orionis, which is also responsible for ionizing the emission nebula IC 434. The much brighter Zeta Orionis is a foreground star, not related to the nebulosity.
The marked change in star density on either side of IC 434 indicates that this strip of glowing hydrogen marks the edge of a substantial dark cloud. As a cloud core emerging from its parent, and as an active site of low-mass star formation, the Horsehead is a fascinating, active, and complex neighborhood. The 'streamers' visible in the brighter region appear to outflowing matter, funneled by a strong magnetic field. Small spots in the Horsehead Nebula's base are protostars in the process of forming.