Instead of using the wide filters needed for true-color imaging, astronomers can use very narrow filters that will reveal the presence of certain atoms or molecules in a given electronic state. And that tells us about the physical conditions of the gas. For example, this image of the sun was taken in the red light of an excited electronic transition of hydrogen gas. All the other light that the sun emits has been blocked by the narrow filter, and this image reveals a very different sun. Notice the furry appearance of the surface .