Researchers use different wavelengths to reveal features not visible in white light.

http://www.lmsal.com/YPOP/Classroom/Lessons/Filters/
"Do you see what I see?": A lesson about the astronomical imaging, how to build a color wheel, and online activities seeing the Crab Nebula at different wavelengths.

http://amazing-space.stsci.edu/light/star-light-science.html
"Star Light, Star Bright" activity has good background information on waves and excellent electromagnetic spectrum diagram.

http://vathena.arc.nasa.gov/curric/space/lfs/emspectr.html
Explains the electromagnetic spectrum through puzzles and question and answer format in easy to understand terms.

http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html
Excellent background information on the electromagnetic spectrum with links to activities and a quiz on the electromagnetic spectrum.

http://coolcosmos.ipac.caltech.edu/cosmic_classroom/ir_tutorial/
NASA's Infrared Processing and Analysis Center's Infrared Astronomy: a terrific site providing background information on infrared astronomy from the days of Herschel to the present. Great infrared images!

http://www.lbl.gov/MicroWorlds/ALSTool/EMSpec/EMSpec.html
Great graphic on the electromagnetic spectrum, and interesting at home experiment on infrared radiation using a TV remote.