Sharpless 212 in Hydrogen and Sulfur . ... CNRS , OHP Explanation: Where do the most massive stars form? ... 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 . ... Sharpless 212 spans about 20 light years and lies about 25,000 light years away. ... NASA Official: Jay Norris. ...