- American Association of Variable Star Observers
- American Astronomical Society
- Astronomical Data from the U.S. Naval Observatory
"The Astronomical Applications Department of the U.S. Naval Observatory computes, from fundamental astronomical reference data, the position, brightness, and other observable characteristics of celestial bodies, as well as the circumstances of astronomical phenomena." The Astronomical Information Center section of this site provides "astronomical data, mainly in tabular form, for use in navigation, surveying, scientific research, litigation, accident reconstruction, and many other activities. Issued annually, the almanacs contain data for one year." The Data Services section of this site provides information of the phases of the moon, eclipses and transits, positions of selected celestial objects, and tables of sunrises/sunsets, etc.
- Astronomical Society of the Pacific
- Astronomy Net
This web site is divided into the following sections: Astronomy, Science and Other Discussion Forums, Astronomy Articles, Astronomy Clubs, Amateur Radio Astronomy Net, Calendar of Events, Constellations, and Image Gallery.
- Astronomy Online
This site is an "information website dedicated to providing up-to-date links and information in all the major topics of Astronomy. It is divided into the following sections: Observation, Science, Solar System, Stars, Our Galaxy, Cosmology, Astrobiology, Exoplanets, Astrophotography.
"The mission of AstronomyLINKS is to provide an index of the best astronomy and space related web sites found around the world on the Internet."
- Eric Weisttein's World of Astronomy
This site is a web encyclopedia with over 588 entries that range in length from definitions to full articles.
- Gazetteer of Planetary Nomenclature
"Planetary nomenclature, like terrestrial nomenclature, is used to uniquely identify a feature on the surface of a planet or satellite so that the feature can be easily located, described, and discussed."
- Google Sky
This site is a collaboration between Google, NASA, the Space Telescope Science Institute, the European space Agency, the Digital Sky Survey Consortium, and the Sloan Digital Sky Survey. This tool "provides and exciting way to browse and explore the universe. You can find the positions of the planets and constellations on the sky and even watching the birth of distant galaxies as seen by the Hubble Space Telescope."
This site is devoted to information about NASA's Hubble Space Telescope. It contains news and photographs of "stars, planets, galaxies, nebulae, and strange celestial phenomena" taken by the telescope; as well as an astronomy reference desk.
- International Astronomical Union
- Journey Though the Galaxy
This site "is a "mini-net" of pages that explores our solar system, stars, extra-solar planets, the theories about the past and future of the universe, and human exploration of space."
- Lunar and Planetary Institute
- Nine Planets: A Multimedia Tour of the Solar System
This site consists of approximately 100 pages, one page for each major body in the Solar System. It is intended for general audiences, little technical background is needed.
- Planetary Society
This Society's mission is to: "Empower the world's citizens to advance space science and exploration. It was founded in 1980 by Carl Sagan, Bruce Murray, and Louis Friedman.
- SAO/NASA Astrophysics Data System
"The SAO/NASA Astrophysics Data System (ADS) is a Digital Library portal for researchers in Astronomy and Physics, operated by the Smithsonian Astrophysical Observatory (SAO) under a NASA grant. The ADS maintains three bibliographic databases containing more than 10.8million records: Astronomy and Astrophysics, Physics, and arXiv e-prints. The main body of data in the ADS consists of bibliographic records."
- Skyview: the Internet's Virtual Telescope
"SkyView is a Virtual Observatory on the Net generating images of any part of the sky at wavelengths in all regimes from Radio to Gamma-Ray." This site is a service of the Astrophysics Science Division at NASA/ GSFC and the High Energy Astrophysics Division of the Smithsonian Astrophysical Observatory.
- Sloan Digital Sky Survey
This site states that it is " one of the most ambitious and influential surveys in the history of astronomy." "Deep, multi-color images covering more than a quarter of the sky and created 3-dimensional maps containing more than 930,000 galaxies and more than 120,000 quasars are provided." Funding comes from a number of private foundations, academic institutions and various governmental agencies from around the world.
- U.S. National Virtual Observatory
"The Virtual Observatory (VO) embodies the concept of large scale electronic integration of astronomy data, tools, and services on a global scale in a manner that provides easy access by individuals around the world. The primary emphasis of the VAO is to provide new scientific research capabilities to the astronomy community."
- Views of the Solar System
This website "presents a vivid multimedia adventure unfolding the splendor of the Sun, planets, moons, comets, asteroids, and more. Discover the latest scientific information, or study the history of space exploration, rocketry, early astronauts, space missions, spacecraft through a vast archive of photographs, scientific facts, text, graphics and videos."