arXiv.org e-Print Archive: Fully automated electronic archive and distribution server for research papers, hosted at the Los Alamos National Laboratory

Astronomy Picture of the Day: Features a different image or photograph of our universe each day, along with a brief explanation written by a professional astronomer

Astrophysics Data System (ADS) Abstracts Service: An astronomy query form

Centre de Données astronomiques de Strasbourg: (CDS) Astronomical databases, bibliography, documentation, and directory

Galaxy Zoo: Interactive project that allows the user to participate in a large-scale project of galaxy research: classifying millions of galaxies found in the Sloan Digital Sky Survey

Hubble Project: Overview, operations, technology, servicing missions, project, news, and image gallery

International Planetarium Society: Organization, events, publications, planetaria worldwide, and resources

NED: The NASA/IPEC Extragalactic Database is built around a list of extragalactic objects with cross-identifications of names, positions and redshifts

SETI@home: Search for Extraterrestrial Intelligence at Home: Currently the largest distributed computing effort with over 3 million users. Participate by running a program that downloads and analyzes radio telescope data. Includes project information, statistics, and forums

The Columbus Optical SETI Observatory: Site dedicated to promoting the Optical Search for Extraterrestrial Intelligence. Here you will find a different approach to The Search For Extraterrestrial Intelligence. The Optical Search For Extraterrestrial Intelligence, otherwise known as Optical SETI (OSETI), seeks to detect pulsed and continuous wave laser beacons signals in the visible and infrared spectrums

The Nine Planets: Overview, sections dedicated to each planet and the smaller bodies - with data, information and some pictures - glossary and appendices

Views of the Solar System: Multimedia tour with statistical data, detailed information, pictures and videos. Also includes educational resources