Beautiful swirling clouds of dust and gas form bright and dark nebulae in the constellation of Orion. These areas are stellar nurseries where stars form when the clouds condense under the influence of gravity...B33, the Horsehead Nebula, is at lower left, and M42, the Great Nebula in Orion, is at upper right...The Horsehead is a dark nebula made of opaque obscuring dust which blocks the light from the nebulae and stars behind it. It is located about 1,500 light years away...The Orion nebula is a complex of red emission nebulae where hydrogen gas glows after being energized by hot young stars, and blue reflection nebulosity, which reflects the light of nearby stars. M42 is located at a distance of about 1,300 light years...Both the Horsehead Nebula and Orion Nebula are part of the much larger Orion Molecular Cloud.