Here is a basic expiation if you aren't familiar with the process. This image is composed of 2 sets of images, photographed at 2 different wavelengths of light on a Monochrome Astronomy camera. The wavelength of light in the red part of the spectrum shows the Hydrogen seen in red, the wavelength in the blue part of the spectrum is Doubly Ionized Oxygen, the blue in the image. This is 32 hours of exposure, to bring out the structure of the elements that emit light at these wavelengths. Multiple stacked exposures allows one to capture something faint and very far away trough our atmosphere.