Horsehead Nebula

The Horsehead Nebula is a dark cloud of gas and dust in the Orion molecular cloud complex, silhouetted against the bright emission nebula IC 434.

IC 434: A bright emission nebula in Orion whose glow provides the backdrop for the Horsehead Nebula. Its hydrogen emission makes the Horsehead's dark outline visible.
Photodissociation region: A boundary layer where ultraviolet radiation changes the chemistry and heating of molecular gas. The Horsehead's illuminated edge is a prominent example of this transition.
Hubble Space Telescope: A space observatory launched in 1990 that observes astronomical objects across ultraviolet, visible, and near-infrared wavelengths. Its visible-light images made the Horsehead's silhouette widely recognizable.
Flame Nebula: An emission nebula near Alnitak, the easternmost star in Orion's Belt. It lies near the Horsehead and shares the same broad star-forming region.
Orion Molecular Cloud Complex: A vast star-forming complex of molecular clouds in the constellation Orion. The Horsehead is one dense feature within this larger cloud complex.
Radiation pressure: The force exerted when electromagnetic radiation transfers momentum to matter. Starlight helps sculpt and compress the cloud's exposed surface.
James Webb Space Telescope: A space observatory designed primarily for infrared astronomy. Its infrared view probes dust and structures hidden in optical images.
Alnitak: The bright multiple-star system Zeta Orionis, at the eastern end of Orion's Belt. Its radiation contributes to the illumination and sculpting of nearby nebulae.
Barnard 33: The dark nebula cataloged as Barnard 33, commonly known as the Horsehead Nebula. This catalog designation identifies the Horsehead itself.
Hydrogen-alpha: A red spectral line emitted by hydrogen atoms during transitions between specific energy levels. Hydrogen-alpha emission makes IC 434 glow behind the dark cloud.

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