Editor's Note: This growing directory is manually maintained and automatically tested for broken links once a month. Links which appear broken for three or more consecutive months are deleted.

Should there be anything wrong with an entry, let me know and I will be glad to correct it.
Note: an entry can appear in several categories.

INSTITUTIONS, Associations and Groups

• International:
• BIPM. Bureau des Poids et Mesures. Home page of the SI System of Units. English version.
• CODATA Committee on Data for Science and Technology.
• ISIS, a A world centre for science with neutrons & muons.
• Light Sources Central site for accelerator-based sources of EM waves.
• Particle Data Group.
• SPIE. International Society for Optical Engineering.
• Europe:
• ASI, Agenzia Spaziale Italiana.
• Astronomical Observatory of Bologna (Italy)
• CERN. The largest European physics research center. (Switzerland)
• DESY. Deutsches Elektronen-Synchrotrone.
• ESA. European Space Agency.
• ESO. European Southern Observatory.
• GSI. Gesselschaft für Schwerionenforschung in Darmstadt, Germany.
• INFN - Istituto Nazionale di Fisica Nucleare (Italy). The National Institute of Nuclear Physics
  runs also the National Laboratories of Gran Sasso (LNGS).
• National Physical Laboratory (UK).
• Nucleonica an official site maintained by the EU.
• Società Italiana di Fisica.
• SRS, the Synchrotron Radiation Source. Closing down!
• University of Bologna, Department of Physics.
• University of Parma, Department of Physics.
• USA:
• American Antigravity, a non-profit organization with a dream.
• American Association of Physics Teachers (AAPT).
• AIP. American Institute of Physics.
• APS American Physics Society. I am a member and it is worth it!
• Argonne National Laboratory. A US Department of Energy laboratory.
• Berkeley National Laboratory.
• Brookhaven National Laboratory.
• FermiLab. Fermi National Accelerator Laboratory, Batavia, Illinois.
• HEP group at Stanford. High Energy Physics.
• HEP group group at Brown University. High Energy Physics.
• Johns Hopkins Applied Physics Laboratory.
• JPL. Jet Propulsion Laboratory.
• KITP. Kavli Institute of Theoretical Physics at University of California, Santa Barbara.
• LLNL. Lawrence Livermore National Laboratory.
• Los Alamos National Laboratory.
• MIT. Massachusetts Institute of Technology.
• NASA. National Space Agency.
• NHMFL. National High Magnetic Field Laboratory at Tallahassee, Florida.
• NIST. Physics at National Institute of Standards.
• NNDC. National Nuclear Data Center.
• NRAO National Radio Astronomy Laboratory.
• NSLS. National Synchrotron Light Source at Brookhaven.
• SLAC at Stanford. Nice links.
• Elsewhere:
• AIST National Institute of Advanced Industrial Science and Technology (Japan).
• IHEP - Institute of High Energy Physics of the Russion Federation Governmental Scientific Center (Russia).
• Landau Institute for Theoretical Physics in Moscow, Russia.
• Laval University Physics Department. (Canada)

JOURNALS, e-Zines, Libraries and Blogs

• AIP journals.
• Journal of Chemical Physics.
• Open Access Physics Journals. Last count: 63.
• Physics. New, excellent, free, online Magazine from tha APS.
• Riviste della Società Italiana di Fisica. In italiano.
• Springer Journals. Includes the European Journal of Physics.
• Wiley Physics website with a complete list of Wiley-Blackwell physics Journals.
• e-Zines:
• Brown University physics news.
• Physics Web. Physics news, jobs and resources.
• The Industrial Physicist. Free, online e-zine.
• Blogs and Forums:
• Sci.Physics.Research,
  a newsgroup intended to facilitate relatively noise-free discussions of issues in and about physics.

ENCYCLOPEDIAs, Dictionaries and Wikis

• Astronomy Thesaurus by the Shobbrooks.
• Encyclopeadia Britannica.
• Magnetismus A-Z, amazing and well done hypertext dictionary of magnetics - in German.
• Microsoft Encarta Dictionary.
• Microsoft Encarta Encyclopedia.
• The Worlds of David Darling. Astronomy, Space, Alternative energy, Sustainable living.
• Units of Measurements Dictionary by Russ Rowlett at UNC.
• Weisstein's Dictionaries (by Eric Weisstein).
• Wikis:
• Wikipedia Free Web encyclopedia.

DATABASES and Directories

• arXive, huge repository of free scientific articles at Cornell University.
• Atomic Energy Collection at Oregon State University.
• CODATA Committee on Data for Science and Technology.
• Constants, units, ... at NIST (National Institute of Standards).
• Constants of Physics and Mathematics. Fundamental constants with SI dimensions.
• HyperPhysics. An amazing physics database at Georgia State University.
• Martindale's Geoscience Center..
• Martindale's Physics Center. Amazing.
• PACS. Physics and Astronomy Classification Scheme (managed by AIP).
• Physical constants and Astronomical data at University of Wisconsin.
• Physical Reference Data. at NIST (National Institute of Standards).
• SI Units and Prefixes.
• SI Dimensions of Physical Quantities. Over 200 quantities in 21 categories.
• Table of Isotopes at Berkeley.
• Universal Nuclide Chart from Nucleonica (a site maintained by the EU).
• Books lists:
• Free online physics books, a list maintained by Stan Sykora.>
• Free Online Textbooks, Lecture Notes, Tutorials, and Videos on Mathematics.
  See the Physics section.
• FreeScience directory of free, online physics books.
  Very valuable resource, thought it counts as books also courses and scripta.
• Mathematical Physics, of Alex Stefanov's math books list at the Trillia Group site.
• MIT Open Courses in Nuclear Science and Engineering. Free.
• MIT Open Courses in Physics. Free.
• Online Lectures at Kavli Institute of Theoretical Physics. Great Science available for free.
• Online physics textbooks by Benjamin Crowell. College level. Free.
• Open source Earth Sciences Textbooks at Textbook Revolution.
• Open source Physics Textbooks at Textbook Revolution.
• Physics Books, a list compiled and maintained by Stan Sykora.
• Physics books on eKnigu in PDF and DjVu fomats. Hundreds of items.
• Physics NetBase, a site of CRC Press.
  They give nothing for free but they sure have their physics books and articles well classified.
• Scribd directory of free, online physics books.
• Tech Books for Free Science section.
• Textbooks in Mathematics by Alex Stefanov
  lists many free, online Mathematical Physics and Applied Mathematics books.
• Link Directories:
• BUBL Link. An amazing collection of physics links, each with a brief description.
• NMR, MRI, NQR and ESR links. A huge, manually managed Magnetic Resonance Directory
• Supernova Pages on the WWW by M.Montes.

NOBEL Prizes and Pioneers

• Nobel Prizes in Physics. See also the complete list.
• Pioneers:

HISTORY and Milestones

• A Brief History of Quantum Mechanics. Appendix to The Strange World of Quantum Mechanics by Dan Styer.
• Biographical memoire of Kenneth T.Bainbridge by Robert V.Pound and Norman F.Ramsey. Mass spectroscopy, Photomultiplier.
• Biographical memoire of R.H.Dicke by W.Happer, P.J.L.Peebles, and D.T.Wilkinson. Quantum theory, Relativity.
• Marconi Society. A great source of information about Guglielmo Marconi.
• Mechanism of the Heavens, a free on-line book by Mary Somerville (1831),
  made available by Malaspina Great Books. 2nd Edition, prepared by Russell McNeil.
• Nuclear Files. Project of the Nuclear Age Peace Foundation. Amazing.
• PV Scientific Instruments. Reproductions of historic instruments.
• Smithsonian Institution. Museums + much more.
• The Hebel-Slichter Effect, a historic and educational essay by Stan Sykora.
• The Modern Revolution in Physics, an online textbook by B.Crowell.
• Milestones:

EDUCATION and Fun

• A list of free online physics books, courses and theses
• Ad Astra Ltd and Early History of Gravity Engineering, an amusing article by Stan Sykora.
• Consciousness, Physics, and the Holographic Paradigm.
  by A.T.Williams. Unusual, stuffed with links and poetry. Worth pondering.
• Extra-Terrestrial Intelligence. A collection of serious articles.
• Home site of Albert Tarantola.
• List of physics laws, rules and other topics in physics and astronomy, by Eric Max Francis.
• Magnetismus A-Z, amazing and well done hypertext dictionary of magnetics - in German.
• MIT Open Courses in Nuclear Science and Engineering. Free.
• MIT Open Courses in Physics. Free.
• Online Lectures at Kavli Institute of Theoretical Physics. Great Science available for free.
• Physics lectures by Fritz Bosch. A few are in English, most in German.
• Servizio dispense presso Dipartimento di Fisica, Uni Roma1. Italiano.
• Superconductors information for Beginners. An excellent web site.
• TeachSpin. Small instruments for teaching Science (mostly physics).
• TelAtomic. Small instruments for teaching Science (mostly physics).
• Textbooks in Mathematics by Alex Stefanov
  lists many free, online Mathematical Physics and Applied Mathematics books.
• The Gibbs Paradox, an interesting 1996 article by E.T.Jaynes.
• The Hebel-Slichter Effect, an educational article by Stan Sykora.
• The Science of Spectroscopy for the advanced.
• Thermal Physics course by Michael Gershenson (Rutgers Uni).
• Thermodynamics, lecture notes by Zoltan S.Spakovszky (MIT). Exhaustive and excellent.
• Thermodynamics & Statistical Mechanics, lecture notes by Richard Fitzpatrick (Uni Texas at Austin). Very extensive, HTML only.
• Fun:
• 1001 things to do with Liquid Nitrogen which you should NOT do!
• Eye tricks. Most amusing.
• Geek stuff shop. See air-zooka, romp pendulum, etc...
• Phun Physics from the University of Virginia.
• Physlink Science e-Store. Science gadgets for kids. Great.
• Planetary puzzles and crosswords collected by Calvin J.Hamilton.
• Science poetry & fun corner in Stan's and Lucia's Log Cabin.
• Science poetry inspired by Astronomy by Stuart Atkinson.

INFO... Articles, Libraries, Reference lists

• Common Data Format (CMD) - a Physics XML supported by NASA.
• Eric Weisstein's physics pages at Mathematica. Excellent.
• Integrity Research Institute. Many out-of-the-chorus articles.
  Zero-point energy, space-worthy propulsion, etc.
• Philosophy of Science Archives at University of Pittsburg.
  Lots of free articles; many about interpretation of quantum physics (over 500 items).
• Solar constant. A brief review by Claus Frölich with 9 references.
• SuperString Theory. The 'official' string theory site
• Unusual Research home page. Links to out-of-the-chorus articles.
• Web site of John Baez.
• Web site of Dan Styer. Quantum physics.
• Articles and other free online texts:
• Articles by Albert Tarantola:
  = Popper, Bayes and the Inverse Problem,
  = Probabilistic Approach to Inverse Problems (with Klaus Mosegaard)
  = Mathematical Basis for Physical Inference (with Klaus Mosegaard)
  = Monte Carlo Sampling of Solutions to Inverse Problems (with Klaus Mosegaard)
  = Inverse Problems = Quest for Information (with Bernard Valette)
  = Generalized Nonlinear Inverse Problems Solved using the Least Squares Criterion (with B.Valette)
  = Three-Dimensional Inversion Without Blocks (with Alexandre Nercessian)
  = Theoretical Background for the Inversion of Seismic Waveforms
  = Nonlinear Inversion of Seismic Waveforms (with Marwan Charara and Christophe Barnes)
  = Noninformative Probability Density for the Elastic Tensor
  = The Mathematics of Continuity
  = A Maxwellian Theory of Gravitation
  and more ...
• Generating Ontology: From Quantum Mechanics to Quantum Field Theory by Edward MacKinnon.
• Is every finite-dimensional Hilbert space a spin-space ?, an article by Stan Sykora.
• Symmetries and Reflections, an essay by E.P.Wigner.
• Why are there 63360 inches per mile?, an article by John Baez.
• Libraries:
• arXive, huge repository of free scientific articles at Cornell University.
• Stan's Library, an online e-Zine edited by Stan Sykora. See the physics section.

Astronomy

• Abrams Planetarium at Michigan State University. They have a nice skywatcher's pages.
• Anglo-Australian Observatory at Epping, NSW (Australia).
• Astronomical Observatory of Bologna.
• Astronomy Thesaurus by the Shobbrooks.
• Astrophysics & Cosmology at Particle Data Group.
• ESA. European Space Agency.
• ESO. European Southern Observatory.
• Hubble heritage project. Don't miss the image gallery page.
• Hubble telescope site.
• Isaac Newton Group of Telescopes (ING) at La Palma (Spain).
• Joint Astronomy Center in Hawai (run by STFC).
• Jodrell Bank Centre for Astrophysics at Uni Manchester, (UK).
• La Silla Paranal Observatory in Chile (run by ESO).
• MERLIN / VLBI the Multi-Element Radio Linked Interferometer Network National Facility, (UK).
• NASA. National Space Agency.
• NASA Image Galleries.
• NRAO National Radio Astronomy Laboratory.
• Rice University Space & Physics.
• SOHO images of the Sun. Near real time and historic.
• Solar eclipse video at the Pakistani Khwarzimic Society web site.
• Sky almanac for skygazers at Star Date magazine (Texas).
• Supernova Pages on the WWW by M.Montes. Amazing collection of links.
• Spitzer Space Telescope's CalTech site.
• The Worlds of David Darling. Astronomy, Space, Alternative energy, Sustainable living.
• Views of the Solar System collected by Calvin J.Hamilton.
• WorldWide Telescope, a nice initiative by Microsoft Research.
• Star catalogues and maps:
• Project Rho starmaps. Intriguing.

Space exploration

• ASI, Agenzia Spaziale Italiana.
• ESA. European Space Agency.
• Extrasolar Planets Encyclopaedia mainained by Jean Schneider. Excellent.
• JPL. Jet Propulsion Laboratory.
• JPL Near-Earth Objects Program.
• JPL near collision simulation.
• JPL Photojournal. Planets etc.
• NASA/Image Galleries.
• NASA/JPL. Jet Propulsion Laboratory.
• NASA/JSC. Johnson Space Center.
• NASA/KSC. Kennedy Space Center.
• NASA/MSFC. Marshall Space Center.
• NASA/JPL. Space events calendar.
• NASA/Spacelink.
• NASA Planetary home page.
• Rice University Space & Physics.
• Science poetry inspired by Space exploration by Stuart Atkinson.
• Space.com at Imaginova Corp.
• SpaceShip One. First successful private spaceship.
• Virgin Galactic. First private space-travel Company.
• Watch on NASA. Not NASA - they just keep an eye on them!
• Extra-Terrestrial Life and/or Intelligence
• Extra-Terrestrial Intelligence. A collection of serious articles.
• Invitation to ETI. Exciting.
• SETI. Search for Extra-Terrestrial Intelligence.
• SETI at home and on your PC! Software download!

SOFTWARE

• Free, opensource and low-cost:
• Free Online Textbooks, Lecture Notes, Tutorials, and Videos on Mathematics.
  See the Software section.
• MegaConverter of measurement units.
• SCILAB, a free and good competitor of MATLAB.
• Web-based converter for basic physical quantities by J.D.Stegeman. Simple and elegant.
• Commercial software:
• Comsol Multiphysics simulation environment. Rather good, but expensive.
• MAGMA home. Magma is a major computational algebra system. Expensive.
• MapleSim at MapleSoft. Multi-domain modeling and simulation. Expensive.
• Matlab home. We all use it at least sometimes, of course. Expensive.

COMPANIES

Separate page: Magnetic Resonance Companies, Magnets and Magnetics

• Cenco Physics. An educational and home-science instrumentation supermarket.
• MapleSoft, home of MapleSim and Maple.
• MathSoft. Home of Matlab.
• Ocean Optics. Affordable VISIBLE, UV and IR spectrometers and optics.
  USB instruments, spectrometers for education, etc.
• Physlink Science e-Store. Science gadgets for kids. Great.
• PV Scientific Instruments. Reproductions of historic instruments.
• TeachSpin. Small instruments for teaching Science.
• TelAtomic. Small instruments for teaching Science.

EVENTS: Conferences, Major Meetings, ...

• APS Meetings & Events calendar.
• Q2Cfestival, Quantum to Cosmos Festival,
  will take place October 15-25, 2009, in Waterloo, Ontarion, Canada.