Imaging is another, more general, term for taking pictures or photographs of something, such as the night sky. Pictures or photographs are usually taken on film, such as you might do with a camera. A camcorder takes images electronically and stores them on videotape. You can't see the images on the videotape by just looking at it, but if you use a VCR, you can see the images that the camcorder saved. Users of the Web are familiar with the GIF images that are stored on computer disks and show up on your computer screen.
Electronic images are much more useful to astronomers than just a picture on film.
A filter only lets certain colors of light pass through it. For example, if you look out the window through a piece of red cellophane, things will look a lot different than they would if you looked through a piece of green cellophane or blue cellophane. By taking images through different filters, such as red, green or ultraviolet filters, scientists can compare the pictures to see how bright an object is in these different colors or wavelengths. The image at the top of this page shows two pictures of the same object, one taken in ultraviolet light, and the other taken in visible light. Often, an object will appear very bright in an image taken through one filter, but very dim in an image taken through another filter.