Horsehead Nebula. Optical image of the region around the Horsehead Nebula in the constellation of Orion. The Horsehead Nebula is the small, distinctive dark dust cloud (centre right) silhouetted against the red cloud IC 434. The hydrogen gas of IC 434 is lit up by hot star Sigma Orionis (bright top centre). The bright star at centre left is Zeta Orionis and the nebula NGC 2024 is visible below it. A dark lane formed by interstellar dust is seen bisecting NGC 2024 at its centre. The two small blue reflection nebulae at lower centre are IC 435 (near bottom edge) and NGC 2023. North is to the left.