It looks like you're using Internet Explorer 11 or older. This website works best with modern browsers such as the latest versions of Chrome, Firefox, Safari, and Edge. If you continue with this browser, you may see unexpected results.
The Astronomy Center is a collection of digital resources for college-level introductory astronomy faculty and students. Astronomy Center is sponsored by the American Astronomical Society, the American Association of Physics Teachers, and the NSF-NSDL.
Science.gov searches over 60 databases and over 2200 selected websites from 15 federal agencies, offering 200 million pages of authoritative U.S. government science information including research and development results.