M27 is the brightest planetary nebula in the northern sky. Planetary nebulae have extremely hot central stars that emit strong ultraviolet radiation. The radiation is in turn absorbed by particles, which then glow brightly (this process is known as fluorescence).
The body of M27 consists of two opposing dark areas (blue in this image) and two broad triangular lobes joined at the center. Because of this structure the nebula was given its more popular name the Dumbbell Nebula.
The Dumbbell Nebula is quite close to our solar system, which in part explains why the image shows such intricate detail: the expanding shell and bright, well-defined edges of the gas cloud are clearly visible.
