 Welcome to our segment on Planetary Nebula. Planetary Nebula represents some of the most beautiful objects in the Milky Way. In this segment, we'll talk about what they are and how far away they are. And I'll show you some of the spectacular pictures taken by the Hubble Space Telescope. But first, I'd like to take a minute to go over how we create these photographs. When someone looks through a telescope, the light from the object falls on a person's eye. To take a photograph, all you have to do is replace the eye with a photographic plate. Here we see Planetary Nebula NGC 2818. It's what someone would see if they were looking through the telescope. It's a wisp. It's very nebulous. So it gets its name nebula, by the way. To the untrained eye, it might look like nothing at all. But if we increase the time exposure and let more and more light from the object fall onto the photographic plate, we get dramatically better results. Get a much sharper image. It's no longer a wisp. You begin to see that there's something serious there with structure. Then, repeating the process with a filter using a small frequency band of light gives us the first pass on color. Repeating this process with different bands and combining the photos produces the full astronomical photo effect. The frequency band chosen can represent different temperatures of gases or different colors might be used to represent different elements present in the nebula. In 2818, we have red representing nitrogen, green represents hydrogen, and blue represents oxygen.