structural:summarization, structural:scholar_edition, quality:correction
Structure

The dark cloud of dust and gas is a region in the Orion molecular cloud complex, where star formation is taking place. It is located in the constellation of Orion, which is prominent in the winter evening sky in the Northern Hemisphere and the summer evening sky in the Southern Hemisphere.

Colour images reveal a red colour that originates from ionised hydrogen gas (Hα) predominantly behind the nebula, and caused by the nearby bright star Sigma Orionis. Magnetic fields channel the gases, leaving the nebula into streams, shown as foreground streaks against the background glow. A glowing strip of hydrogen gas marks the edge of the enormous cloud, and the densities of nearby stars are noticeably different on either side.

Heavy concentrations of dust in the Horsehead Nebula region and neighbouring Orion Nebula are localized into interstellar clouds, resulting in alternating sections of nearly complete opacity and transparency. The darkness of the Horsehead is caused mostly by thick dust blocking the light of stars behind it. The lower part of the Horsehead's neck casts a shadow to the left. The visible dark nebula emerging from the gaseous complex is an active site of the formation of "low-mass" stars. Bright spots in the Horsehead Nebula's base are young stars just in the process of forming.