Henderson, Tom (1998). The Physics Classroom. Retrieved April 7, 2007, from The Physics Classroom Web site: http://www.physicsclassroom.com/Default2.html
The physics classroom is an excellent resource for both teachers and students. The website is structured as an online study guide and covers most of the basic concepts in physics. It has wonderful animations which help explain difficult questions. It also has questions at the end of most sections with answers that have been carefully explained.
White, Nicholas (2004). Dark Energy - Introduction. Retrieved April 7, 2007, from NASA's Imagine the universe Web site: http://imagine.gsfc.nasa.gov/docs/science/mysteries_l1/dark_energy.html
Boen, Brooke (2007). Exploring the invisible universe: Chandra X-Ray Observatory. Retrieved April 7, 2007, from NASA Web site: http://www.nasa.gov/mission_pages/chandra/main/index.html
Russell, Randy (2004). Fundamental Physics. Retrieved April 7, 2007, from Windows to the Universe Web site: http://www.windows.ucar.edu/tour/link=/physical_science/physics/physics.html&edu=high
Canright, Shelley (2007). Stars. Retrieved April 7, 2007, from NASA Web site: http://www.nasa.gov/audience/foreducators/topnav/subjects/spacescience/Stars.html
This is general collection of Star resources for Educators on NASA's website.
Easily accessible for students; couldn't find specific credits, though
Payne, W. E. (2001). Exploring the electromagnetic spectrum. Retrieved July 19, 2007, from Altair Web site: http://www.altair.org/index.html
Great web resource. It is also available in Spanish and Italian.
Thaller, M (2007). Cool Cosmos. Retrieved July 19, 2007, from Cool Cosmos Web site: http://coolcosmos.ipac.caltech.edu/
Great website from NASA's JPL. Also comes in Spanish.
Smith, DeLee (2007, January 26). In a Different Light. Retrieved July 19, 2007, from Star Gazers - Educators Web site: http://stargazers.gsfc.nasa.gov/educators/in_different_light/iadl_table_contents.htm
This site from NASA contains a number of lessons using the electromagnetic spectrum
Bothun, G (2007). Elements. Retrieved July 19, 2007, from Atomic spectrum by element Web site: http://jersey.uoregon.edu/elements/Elements.html
This University or Oregon site is an interactive Java applet that lets you click on a element and it will display either the absorption spectrum or the emission spectrum.
Jircitano, A. J. (2007, May 7). Periodic Table of Elements. Retrieved July 19, 2007, from Periodic Table Web site: http://chemistry.bd.psu.edu/jircitano/periodic4.html
This Penn State website allows the user to click on an element and its emission spectrum.