M27 is the second largest planetary nebula in the sky and a typical member of the bipolar variety of this kind of nebulas. Because of its shape it is also called "Dumbbell Nebula".
It is an example of what will happen to our sun in about 5 billion years. After nuclear fusion processes have come to an end the outer layers of the dying sun are shed off. The still very hot core is exposed and its radiation excites hydrogen ( red) and oxygen ( greenish blue) to glow.