• arXiv Preprint Server (Cornell Univ.) - physics, mathematics, non-linear science and computer science
  • arXiv Mirror Site (Los Alamos National Laboratory)
• Astronomy Thesaurus (Australian National Univ.) - Searchable in 5 languages.
• BookFinder.com - one of the best & largest meta-search site for new & used books.
• Digital Library for Physics, Astrophysics, and Instrumentation Astrophysics Data System (ADS) from NASA/Harvard Univ.
• Directory of Open Access Journals (Lund Univ.) - Over 2,700 peer reviewed, freely available journals, the most comprehensive directory on the Web.
• Directory of Open Access Repositories -OpenDOAR (Univ. of Nottingham) - an authoritative directory of academic open access repositories.
• Encyclopedia Astronautica (Mark Wade) - an excellent history of spaceflight and space vehicles around the world.
• Fundamental Physical Constants (NIST)
• Handbook of Space Astronomy and Astrophysics (Cambridge Univ. Press)
• Journal Info (Lund University) - Basic data and interesting statistics for open access and subscription journals worldwide.
• Journal-Ranking.com (Andrew Lim, Hong Kong Univ. of Science & Technology) - Free iinteractive journal ranking service allowing users to choose ranking parameters. Alternative to ISI journal impact factors.
• OAIster - collection of digital open access/open archive documents (Univ. of Michigan)
• Publish or Perish (Anne-Wil Harzing) - a downloadable, free program analyzing Google Scholar citations to an author's publications. Reports statistics such as ave. cites per paper and h-index & related metrics. Disclaimer: Google Scholar citation data is very noisy & includes non-peer reviewed citing documents.  Citation variations likely inflate number of papers & citations.
• RoMEO - Over 400 publisher copyright and self-archiving policies (SHERPA)
• Scientific and Technical Acronyms, Symbols, and Abbreviations (Wiley Interscience)
• Scientific Commons (Univ. of St .Gallen) - Over 15 million open access articles and other documents
• Scitopia - Metasearch (one-pass) searching of over 3.5 million references from 21 science & engineering societies.
• SciVee (Univ. of California, San Diego) - Allows scholars to post articles along with a video presentation. Sponsored by NSF & Public Library of Science.
• WNY Libraries Virtual Union Catalog (Western New York area libraries holdings)

• American Astronomical Society Job Register
• NASA Jobs
  • Career & Research Opportunities for College Students
• Naturejobs (Nature Magazine)
• Optics.Org Employment Service (Institute of Physics)
• PhDs.org: Science, Math & Engineering Career Resources (Geoff Davis) - aims at Ph.D. candidate & job seekers.  Includes school rankings at Find the Graduate School That's Right for You.
• Space Careers (Spacelinks) - Space industry commercial job service.
• SPIE Employment Service (International Society for Optical Engineering).

• Astronomical Almanac Online [Nautical Almanac Office (U.S.)/Her Majesty's Nautical Almanac Office/(U.K.)]
• Astronomical Data Archives Center (ADAC) (National Astronomical Observatory of Japan)
• Astronomical Data Center (ADC) - As of 10/1/2002, all updating and maintenance terminated by NASA. Ported to University of Maryland which is maintaining the site, but not updating it.
• Astrophysics Data System (ADS) - Digital Library for Physics, Astrophysics, and Instrumentation (NASA/Harvard Univ.)
• Frequencies for Observed Interstellar Molecular Microwave Transitions (NIST)
• NASA/IPAC Extragalatic Database - Includes LEVEL5 knowledgebase.
• NIST Data Gateway - Access to all databases available from NIST's Standard Reference Data (SRD) collections.
• Parallax Project Historic Star Data - Star parallax data and calculations from 1910-1969, originally, the Publications of the Allegheny Observatory of the University of Pittsburgh in 10 volumes.
• SIMBAD Astronomical Database (Centre de Données astronomiques de Strasbourg) - data on astronomical objects outside the solar system.
• US National Virtual Observatory - meta search of data collections, catalogs, and image archives

• Astronomy and Cosmology on Stamps (UB SEL) - Exhibit of postage stamps with astronomical themes
• Astronomy Center (National Science Digital Library/NSF) - Clearinghouse of digital resources, teaching aids, news, & learning tools.
• Astronomy Education Review (Association of Universities for Research in Astronomy) - New ideas and resources for teaching and outreach in space sciences.
• Astronomy Software Servers (Astroweb) - Over 100 sites and codes listings that are used in astronomical research.
• NASA Education Center
• Physics and Astronomy Departments Around the World (Physlink)
• Planetary Science Research Discoveries (Univ. of Hawaii) - collection of online articles, resources, news, and classroom activities.
• Project CLEA: Laboratory Exercises in Astronomy (Gettysburg College)
• Science Animations (North Harris Community College) - Directory of animations, movies, and interactive tutorial links available on the web.
• SciTalks: Smart people on cool topics (Lee Vodra) - Excellent science videos, many by propminent researchers. Caution: Videos are self posted. Copyright & accuracy uncertain.
• Space Physics Textbook (Space Physics Group of Oulu)
• Symbols.com- Over 2,500 Western signs and ideograms with a unique graphic description search, e.g. symmetric vs. non-symmetrical
• Writing Guidelines for Engineering and Science Students (Penn State Univ.) - a particularly useful and comprehensive guide to good scientific writing.

• About.com Astronomy Directory
  
• Astronomical Resources on the Internet (Univ. of Denver)
• AstroWeb Consortium (NRAO) - Data, people, publications, organizations, research
• NASA Home Page - Links to the space agency and more.
  • Life Sciences Data Archive - Including mission overviews and image library
• National Science Digital Library - funded by major NSF grants.
• Resources in Astronomy (Special Libraries Association Physics-Astronomy-Mathematics Div.)
• Science.gov "FirstGov for Science" gateway.
• Scirus (Elsevier) - search engine for scientific information
• Virtual Astronomy, Astrophysics, and Space Reference Center - Martindale's Reference Desk
• WorldWideScience.org - Open access portal & federated search engine covering over 15 countries

• Anglo-Australian Observatory of Astronomical Images - Striking wide-field photographs
• Astronomy Images Directory - Pretty Pictures (NRAO) - Over 100 sites listed, from Hubble to the space shuttle to comet Shoemaker-Levy 9.
• Constellation and star guide (Univ. of Wisconsin) -when they are best seen and interactive sky charts.
• Interactive Sky Chart (Sky and Telescope magazine) -View an image of the sky from any location on earth.Free registration required.
• The Messier Catalog - Focuses on the most beautiful nebulae, star clusters, and galaxies (SEDS)
• NASA Images - Metasearch of over 21 major NASA image collections (NASA/Internet Archive)
• Smithsonian Astrophysical Observatory Telescope Data Center

• Habitable Worlds (NASA) - explore each planets potential for supporting life with many facts and photos about each planet.
• Map-a-Planet (USGS/NASA) - create customized maps of planets and moons.
• NASA Human Spaceflight - Information about the International Space Station and a launch countdown clock plus links to the Space Shuttle page and the history of manned space flight.
• NeoDys: Near Earth Objects - Orbital data on all Near Earth Asteroids and impact risk analysis.
• The Nine /Eight/ Planets - a Visual tour of the solar system. (Univ. of Arizona)
• Northern Lights (Nordlyssenteret AS) - Earths Aurora
• Planetary, Lunar, and Stellar Visibility (Alcyone Software) - freeware program that produces color diagrams showing when astronomical objects are visible during any year from 3000 BC to AD 6000 at any location on the earth.
• Solar System Simulator (NASA) - Software that visualizes solar system objects from many perspectives based on user-specified parameters.
• View of the Solar System: Lesson Plans and Activities (Calvin J. Hamilton)
• Lunar and Planetary Institute (Universities Space Research Association)
  • Exploring the Moon . Histories and images, etc. on all the Lunar missions.
  • Lunar Atlases . Four atlases are online in digital form
  • Lunar Topographic Orthophotomap (LTO) Series . Digital images of 1:250,000 scale maps produced by the Defense Mapping Agency.
  • Planetary Science Websites
• U.S. Naval Observatory - Extensive astronomical data such as sun and moon rise and set times, moon phases, eclipses, seasons, and positions of solar system objects. Information on software, research, and publications.