Clouds of the Carina Nebula.

What forms lurk in the mists of the Carina Nebula? The dark ominous figures are actually molecular clouds , knots of molecular gas and dust so thick they have become opaque . In comparison, however, these clouds are typically much less dense than Earth's atmosphere . Featured here is a detailed image of the core of the Carina Nebula , a part where both dark and colorful clouds of gas and dust are particularly prominent. The image was captured last month from Siding Spring Observatory in Australia . Although the nebula is predominantly composed of hydrogen gas -- here colored green, the image was assigned colors so that light emitted by trace amounts of sulfur and oxygen appear red and blue, respectively. The entire Carina Nebula , cataloged as NGC 3372, spans over 300 light years and lies about 7,500 light-years away in the constellation of Carina. Eta Carinae , the most energetic star in the nebula, was one of the brightest stars in the sky in the 1830s, but then faded dramatically .