• NASA Astrophysics Data System - abstracts on astrophysics, astronomy, instrumentation, geophysics, and physics. Plus the Los Alamos preprint server, articles, and catalogs.
• Simbad - brings together basic data, cross-identifications, observational measurements, and bibliography, for celestial objects outside the solar system: stars, galaxies, and nonstellar objects within our galaxy, or in external galaxies.
• Science for the Millennium - online expo focusing chiefly on astronomy and astrophysics, advanced computation, and virtual environments.
• Hands On Universe - enables students to investigate the Universe while applying tools and concepts from science, math, and technology.
• Astronomy Thesaurus - astronomy terms in English, French, German, Spanish and Italian; all terms cross referenced.
• Space Place - make a pop rocket that really works, solve a riddle, and dive beneath the surface of Mars. Do these things and more, and learn about space and astronomy at the same time.
• SkyView - a "virtual" observatory dynamically generating images of the sky in different wavelength regimes from a static image database, intended as a quick look facility to see the heavens.
• Canadian Astronomy Data Centre - distribution center for observatory archives, catalogues, and more.
• #astronomy
• AbsoluteAstronomy.com - general facts and statistical information about planets, moons, constellations, stars, galaxies, and Messier objects.
• Aladin Java: A Sky Atlas - an interactive atlas allowing the viewer to visualize digitized images, superimpose entries from astronomical catalogs, and access data from databases.
• Astro!nfo - service of the Swiss Astronomical Society.
• Astronomy and Astrophysics at NSSDC
• Astronomy for Kids - astronomy site specifically designed for kids and their parents.
• Astronomy HyperText Book
• Astronomy In Your Face - space pictures, movies, animations, links, and more.
• Astronomy Interactive Network - detailed information about radio, optical, physics and the history of astronomy; with games, pictures, quizzes, glossary, timeline, links, and message boards.
• Astronomy On-Line - the world's biggest astronomy event on the Web. Groups from around the world experience the excitement of real-time scientific adventure and the virtues of international collaboration.
• Astronomy Sight, The
• Astronomy Thesaurus - astronomy terms in English, French, German, Spanish and Italian; all terms cross referenced.
• Bad Astronomy - righting wrong ideas.
• Beyond Earth - a guide to everything not on Earth.
• Beyond Our Skies: Discovering the Cosmos - ThinkQuest project presenting the history and basics of astronomy.

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• Canadian Astronomy Data Centre - distribution center for observatory archives, catalogues, and more.
• Hands On Universe - enables students to investigate the Universe while applying tools and concepts from science, math, and technology.
• Imstar - Astronomy links and some of our own CCD images
• Journey into the Heavens - astronomy guide presenting information about our solar system, constellations, the evolution of the universe, space missions, astronomers, and more.
• Messages from Outer Space - tour the Moon, Meteorites, and Solar System Gallery at the National Museum of Natural History. Includes many educational activities and resources.
• Munich Astronomical Archive - data on astronomical objects.
• NASA Astrophysics Data System - abstracts on astrophysics, astronomy, instrumentation, geophysics, and physics. Plus the Los Alamos preprint server, articles, and catalogs.
• Nick Strobel's Astronomy Notes - complete astonomy textbook for first-year college courses.
• Online Planetarium Show - educational site about the discoveries of the Hubble Space Telescope, historical astronomers, mythology, and light pollution.
• Orbital 9 - forum based web site where people can discuss topics about the solar system, spacecraft missions, and other science and astronomy related interests.
• PlanetDiary - presents weekly geological, astronomical, meteorological, biological, and environmental news from around the globe, plus Internet activities and links to science resources.
• Science for the Millennium - online expo focusing chiefly on astronomy and astrophysics, advanced computation, and virtual environments.
• Sea and Sky - explore the splendors of the sea and the wonders of the universe through information, images, sounds, links, and interactive games.
• Simbad - brings together basic data, cross-identifications, observational measurements, and bibliography, for celestial objects outside the solar system: stars, galaxies, and nonstellar objects within our galaxy, or in external galaxies.
• Sky Guide - offers information about amateur astronomy, including observation, telescopes and accessories, and astrophotography.
• SkyView - a "virtual" observatory dynamically generating images of the sky in different wavelength regimes from a static image database, intended as a quick look facility to see the heavens.
• Space Place - make a pop rocket that really works, solve a riddle, and dive beneath the surface of Mars. Do these things and more, and learn about space and astronomy at the same time.
• SpaceLink
• Star Journey - journey through the stars with National Geographic. Includes a Star Chart with overlays of images from the Hubble Telescope.
• Stellar Neigborhood in VRML - thrilling 3-D ride through interstellar space within 25 parsec of the sun. Database contains nearly 3000 stars.
• Tonight's Sky - designed to guide your eye to something you can see that night, or the next morning before dawn.
• Tour the Cosmos - a multimedia foray into the mysteries of the universe.
• Web Window to the Invisible Universe - A view into the invisible universe as seen through two of the world's largest radio telescopes.
• Why Is the Sky Dark at Night? - colorful Java applets guide you through the fascinating physics problem.
• FAQ - sci.astro - sci.astro is a newsgroup devoted to the science of astronomy. Its content ranges from the Earth to the farthest reaches of the Universe

• Astronomical Applications
• Astronomical Calendar - make an astronomical calandar by tracing a pole's shadow on the summer and winter solstice, and the equinox.
• Astronomical Sky Calendar
• Astronomy - What's Up This Month - monthly updates on astronomical events, star charts for the month, photos, charts, and more.
• Celestial Times
• Compute Local Apparent Sidereal Time - an online form. Astronomers use local sidereal time because it corresponds to the coordinate right ascension of a celestial body that is presently on the local meridian.
• Cosmicdust - monthly celestial events.
• ESO Sky Calendar Tool - produces a nightime calendar of phenomena for a single site.
• Heavenly Details
• Madsci's Observatory - astronomical phenomena good for viewing, until the year 2010.
• Peter's Astronomical Calendar - a listing of upcoming astronomical events of interest to amateur astronomers.
• Space Calendar - covers space-related activities and anniversaries for the coming year, including links to related home pages.
• Stig's Sky Calendar - explore the yearly dance of the Sun, Moon and planets.
• Study of Stars - into to stars and the phenomena related to them.
• Terry's Hunt of the Month - monthly observing list with objects to look for from Messier, Herschel, Herschel II, FWAS Favorites, and The Beyond Messier observing lists.

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Formulas & Constants

• Eric's Treasure Trove of Astronomy  - online encyclopedia of astronomy formulas and derivations.
• Astronomy Formulas - periodicity formulas, time formulas, illumination geometry, miscellaneous formulas, definitions, notation.
• Constants and Equations for Space-Related Calculations
• Constants and Equations Pages, The - comprehensive reference for astronomy, science, and math.
• Graham Pattison's Telescope Formulas
• Trigonometry And Astronomy - equation which shows how astronomers measure the distance to stars.
• Àryabhatíya of Àryabhata - 1,582,237,500 rotations of the Earth equal 57,753,336 lunar orbits, an extremely accurate ratio. Àryabhata was born in 476 in India.

• Value Software
• AIPS ("Classic", not aips++) - Astronomical Image Processing System is a software package for calibration, data analysis, image display, plotting, and a variety of ancillary tasks on Astronomical Data.

• Astronomy Freeware - download astronomy freeware and shareware.
• Dictionary of Astronomy
• Earth Centered Universe, The - a shareware general purpose planetarium and telescope control program for Windows.
• Home Planet - freeware to display planets and star maps.
• Image Reduction and Analysis Facility - a general purpose software system from the National Optical Astronomy Observatories for the reduction and analysis of astronomical data
• Physics/Astronomy Applets - interactive Java curriculum modules from the University of Oregon Physics department. Topics include mechanics, energy, thermodynamics, and astrophysics.
• PlanetWatch shareware - A multimedia atlas and simulation of our solar system for Windows 3.1 or better.
• Program to Load Astronomy and Cosmography Data - program was created to load a programmable HP 48.
• PROGRAPE-1 - programmable special purpose computer for many-body simulations.
• SkyDraw - get a map showing the positions of the Sun, Moon, planets, and stars for times and locations you specify.
• Sun, Moon & Earth Applet - displays the positions of sun and moon for any date, time, and location on an interactive world map with day and night regions.
• Ultimate Messier Object Log, The - freeware database that contains relevant information for all 110 Messier Objects and various layouts to assist amateur astronomers in documenting their search for deep sky objects.

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Phases of the Moon

• Moon Phase Calendar  - graphic representation of the phase of the moon for each day of the month.
• Lunar Calendar - calculates and displays three complete lunar cycles based on a start date of your choice.
• Lunar Outreach Services - real time phase and age of the moon.
• Moonsighting.com - find out where on Earth you can view the lunar crescent after a new moon.
• Moonstick Information Site - description of a slide-rule moon-phase calculator.
• Once in a Blue Moon - includes a blue moon calculator.
• View of the Moon - see what the moon looks like on a certain date. Includes related data as well.
• Virtual Reality Moon Phase Pictures - view the phase of the moon for any date and time from 1800 through 2199 AD.

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Lunar Calendar

• Goddess Lunar Calendar - in this calendar, years have 12 or 13 months, which are named after goddesses from various cultures.
• Lunar Calendar in Japan
• Lunar Calendars
• Yerm Lunar Calendar - a simple constructed rule-based pure lunar calendar.

• Amateur FITS Archive (AFA) - public archive of amateur CCD pictures in Flexible Image Transport System format.
• Astro-Photography Mailing List (APML) Archives
• Astronomy and Astrophotography - short introduction of an amateur showing easy ways to begin with astrophotography.
• Astrophoto Of the Week - new amateur astrophoto is posted every Monday which was taken with in the previous week.
• Basic Primer on Astrophotography
• CCD-world - listserv and resource archive for the development and use of CCDs and short wave infrared (SWIR) detectors in professional astronomy.

• Comet and Sky Astrophotography
• MrEclipse.com - the ultimate resource for eclipse photography, featuring eclipse photo galleries and reports, by Fred Espenak.
• Oort Crowd
• Web Directory: Photo Resource - Astrophotography

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Lunar Eclipse

• How to Photograph a Lunar Eclipse - adapted from Sky & Telescope.
• Lunar Eclipse Images - photographs taken during the total lunar eclipse that took place on April 3-4, 1996.
• Lunar Eclipse Photo Gallery - photographs by Fred Espenak.

• Structure and Evolution of the Universe - NASA's quest to understand the Universe: its evolution, structure and ultimate fate.
• NASA Astrophysics Data System - abstracts on astrophysics, astronomy, instrumentation, geophysics, and physics. Plus the Los Alamos preprint server, articles, and catalogs.
• Simbad - brings together basic data, cross-identifications, observational measurements, and bibliography, for celestial objects outside the solar system: stars, galaxies, and nonstellar objects within our galaxy, or in external galaxies.
• Imagine the Universe! - dedicated to discussion about the universe, how it is evolving, and the kinds of objects and phenomena it contains. A service of NASA's High-Energy Astrophysics Learning Center.
• Ask a High-Energy Astronomer 
• Ask a High-Energy Astronomer 
• Advanced Composition Explorer (ACE) - online data, documentation, instruments, news, and more.
• Astronomer's Telegram - resource for reporting and commenting on new astronomical observations in the astrophysics community.
• CATS Database - astrophysical CATalogs support System.
• Common Astrophysics Acronyms
• Geometrical Physics - astrophysicist Jean-Pierre Petit presents his research in physics, cosmology, astronomy and mathematics. In French and English.
• History of High-Energy Astrophysics - a list of many important dates in the history of high-energy astrophysics and astronomy in general, with links to further details.
• Hubble Constant - one of the most important numbers in cosmology because it is needed to estimate the size and age of the universe.
• HubbleConstant.com - information on the Hubble Constant, cosmology, and the size and age of the Universe.
• Imagine the Universe! - dedicated to discussion about the universe, how it is evolving, and the kinds of objects and phenomena it contains. A service of NASA's High-Energy Astrophysics Learning Center.
• M.I.T. Space Plasma Group
• Mordrin's Astrophysics Site - dedicated to astrophysics/astrophyiscists.
• NASA Astrophysics Data System - abstracts on astrophysics, astronomy, instrumentation, geophysics, and physics. Plus the Los Alamos preprint server, articles, and catalogs.
• Ned Wright's Cosmology Tutorial - illustrated introduction to modern observational cosmology and the Big Bang Model. Includes FAQs and cosmological fads and fallacies.
• Nuclear Astrophysics Data
• Origins of Structure in the Universe - Canadian Astronomy and Astrophysics in the 21st Century.
• Scientific American: Mapping the Universe - using techniques drawn from the analysis of music, astronomers have been studying how galaxies form into progressively larger groupings.
• Shapley - Curtis Debate in 1920 - guide to understanding all facets of the Great Debate between Harlow Shapley and Heber D. Curtis over the scale of the universe. Includes a complete transcript.
• Simbad - brings together basic data, cross-identifications, observational measurements, and bibliography, for celestial objects outside the solar system: stars, galaxies, and nonstellar objects within our galaxy, or in external galaxies.

• Solar System's Dynamic Stability Revised
• Space Interferometry Mission (SIM) - will be NASA's first space interferometer designed specifically for measuring the position of stars.
• Space Time Mass - the fabric of space-time is another state of matter and hence it has equivalent mass. The missing mass of the Universe is in the space-time itself that fills the cosmos.
• Spectrashift.com - dedicated to amateur redshift measurements. This site gives information on spectroscope construction, software processing, data examples, and more.
• Structure and Evolution of the Universe - NASA's quest to understand the Universe: its evolution, structure and ultimate fate.
• WebStars: Astrophysics in Cyberspace

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Galaxies

• NASA/IPAC Extragalactic Database (NED)
• Scientific American: Constructing the Cosmos - observations of galaxies keep yielding new patterns, but how meaningful are they?
• University of Texas at Austin - Galaxy Formation and the Intergalactic Medium Research Group
• 2dF Galaxy Redshift Survey - goal is to secure high quality spectra and redshifts for 250,000 galaxies brighter than bJ=19.5 (extinction-corrected), with a deeper extension to R=21 making best use of good conditions.
• CNOC - Canadian Network for Observational Cosmology - redshift surveys and profiles of clusters.
• IRAS PSC Redshift Survey - a redshift survey of some 15,500 galaxies detected in the IRAS Point Source Catalogue over 83% of the sky.
• Las Campanas Redshift Survey - redshifts for galaxies selected from a CCD-based catalog measured in a Kron-Cousins R-band. The survey covers over 700 square degrees in 6 strips.

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Gamma Ray Observations

• BATSE: Burst and Transient Source Experiment - high energy astrophysics experiment in orbit around Earth which studied the phenomenon of gamma-ray bursts, although the detectors also recorded data from pulsars, black holes, and other exotic astrophysical objects.
• Compton Gamma-Ray Observatory Science Support Center - second of NASA's Great Observatories. Had four instruments that covered six decades of the electromagnetic spectrum, from 30 keV to 30 GeV.
• Fred Lawrence Whipple Gamma-Ray Observatory - primary emphasis of the research is the search for and study of celestial sources of very high energy (VHE) gamma-rays in the energy range of 100 GeV - 10 TeV.
• GLAST: Exploring the Astrophysics of Extremes
• GLAST: Gamma Ray Large Area Space Telescope - a proposed orbiting instrument for observing high-energy gamma rays.
• LOTIS Experiment - Livermore Optical Transient Imaging System is a search for simultaneous optical counterparts of gamma-ray bursts.