We obtained information and illustrations for this article from the following sources:

Hubble Space Telescope (HST) News from the Space Telescope Science Institute, NASA, and the European Space Agency (ESA):

http://oposite.stsci.edu/pubinfo/pr.html

Images from High-Energy Astrophysics Missions, a Web site maintained by NASA's High Energy Astrophysics Science Archive Center:

http://heasarc.gsfc.nasa.gov/images/

The image gallery of NASA's Compton Gamma Ray Observatory:

http://cossc.gsfc.nasa.gov/cossc/PR.html

Astronomy Picture of the Day, a service of NASA's Laboratory for High Energy Astrophysics:

http://antwrp.gsfc.nasa.gov/apod/archivepix.html

Students for the Exploration and Development of Space (SEDS), a site hosted by the University of Arizona Chapter at the Lunar and Planetary Laboratory:

http://seds.lpl.arizona.edu/

Photographs from the Anglo-Australian Observatory:

http://www.aao.gov.au/images.html

Images from the Lund Observatory, Sweden:

http://www.astro.lu.se/imagery.html

News and images from the Nuffield Radio Astronomy Laboratories, Jodrell Bank, UK:

http://www.jb.man.ac.uk/news/

The homepage of Prof. Bruce Margon, Department of Astronomy, University of Washington, Seattle, WA:

http://www.astro.washington.edu/margon/

An international data and information page of the Variable Star Network (VSNET) at the Department of Astronomy, Kyoto University:

http://www.kusastro.kyoto-u.ac.jp/vsnet/index.html

The Super-Kamiokande Web site at the University of California, Irvine:

http://www.ps.uci.edu/~superk/

The images of Henry Norris Russell and Ejnar Hertzsprung came from pages of the Department of Astrophysical Sciences of Princeton University and the Lake Afton Public Observatory of the Physics Department of Wichita State University, respectively:

http://www.astro.princeton.edu/facpage.html
http://156.26.14.23/lapo/lss/hertz.htm and
http://www.twsu.edu/~obswww/

Additional images and information about stellar astronomy and the space sciences can be found in our Space Science section and our Observations of the Week archive:

http://observe.ivv.nasa.gov/nasa/space/space_index.shtml
http://observe.arc.nasa.gov/nasa/ootw/1998/oarch98_index.html