July 29, 2011 - Time
The universe is capable of some pretty spectacular displays, but few things approach the cosmic grandeur of a planetary nebula. The "planetary" part has to do with the formation's shape, which is roughly spherical, like a planet. But these objects are a lot bigger than any planet or even any star. They're enormous clouds of gas — like smoke rings, but bubble-shaped — puffed out by sun-like stars undergoing their death throes. In 5 billion years or so, our own sun may well emit a gorgeous belch of its own, perhaps to be noted by alien astronomers somewhere out in the Milky Way.
...