Astronomy Picture of the Day

Explanation: Blown by the wind from a massive star, this interstellar apparition has a surprisingly familiar shape. Catalogued as NGC 7635, it is also known simply as The Bubble Nebula. This colourful telescopic image includes a long exposure through a hydrogen alpha filter to reveal details of the cosmic bubble and its environment. Although it looks delicate, the 10 light-year diameter bubble offers evidence of violent processes at work. Above and right of the Bubble's centre is a hot, O-type star, several 100,000 times more luminous and approximately 45 times more massive than the Sun. A fierce stellar wind and intense radiation from that star has blasted out the structure of glowing gas against denser material in a surrounding molecular cloud. The intriguing Bubble Nebula lies a mere 11,000 light-years away toward the boastful constellation Cassiopeia.