The star cluster Pismis 24 lies in the core of the large emission nebulaNGC 6357, which extends one degree on the sky in the direction of the constellation Scorpius. Part of the nebula is ionised by the youngest (bluest) heavy stars in Pismis 24. The intense ultraviolet radiation from the blazing stars heats the gas surrounding the cluster and creates a bubble in NGC 6357. The brightest point of light above the centre of this image is Pismis 24-1, once thought to be the most massive known star but now known to be a binary system.
The Horsehead Nebula (also known as Barnard 33 in emission nebula IC 434) is a dark nebula in the constellation Orion. The nebula is located just to the south of the star Alnitak, which is farthest east on Orion’s Belt, and is part of the much larger Orion Molecular Cloud Complex. The nebula was first recorded in 1888 by Scottish astronomer Williamina Fleming on photographic plate B2312 taken at the Harvard College Observatory. The Horsehead Nebula is approximately 1500 light-years from Earth.