Image: Digitized Sky Survey
In this visible-light image, the Horsehead Nebula appears to rise from a vast dark cloud of gas. Many more stars are visible above the nebula, where the dust is thinner, than below it, where the dust is denser. A large, bright star called Sigma Orionis dominates the upper part of the image. Sigma Orionis is a hot star that gives off lots of energetic ultraviolet light, causing the pink glow along the edges of the nebula.