The Horsehead Nebula, also known as Barnard 33 (B33), is a dark nebula in the constellation Orion. It is easily recognized by its distinct silhouette of a horse head against a glowing background of gas. Its unique shape has made it one of the most famous and photographed deep-sky objects. 

Located about 1,300 to 1,600 light-years away, the nebula is approximately 3.5 light-years in height and 2.5 light-years across.

The nebula is a cloud of gas and dust that absorbs visible light from the emission nebula behind it. The red glow in the background is hydrogen gas ionized by UV radiation from the star Sigma Orionis. It is part of the larger Orion Molecular Cloud Complex, which is a star-forming region including the Great Orion Nebula and the Flame Nebula.

New, low-mass stars are forming within the dense molecular clouds at the base of the Horsehead’s neck. The intense UV radiation from young stars in the region is eroding the nebula.