Sharpless 212 in Hydrogen and Sulfur

Explanation: Where do the most massive stars form? Observational evidence indicates that the outskirts of developing open clusters of stars are primary locations. Pictured above is one such open cluster: Sharpless 212. Visible in the image center are massive stars in the open cluster . The energetic light from these stars ionizes surrounding hydrogen atoms creating an HII region . As the hydrogen atoms re-acquire electrons , they emit the red light highlighted. Sharpless 212 also contains small amounts of dust and heavy atoms such as Sulfur . The dust efficiently absorbs light, while emission from Sulfur is highlighted in blue. Particularly striking and well-defined boundaries that separate the ionized material from surrounding neutral material are visible at the edge of the HII region . Sharpless 212 spans about 20 light years and lies about 25,000 light years away.