For Hobbyists

JPL Space Calendar
If it has anything to do with Astronomy or Space Sciences - it's here!

StarDate Online
From the University of Texas McDonald Observatory. StarDate keeps you in touch with the universe with detailed skywatching information, in-depth features, the latest astronomy news, and more.

The Sky - Astronomy Calendar
This is a simple but useful site that gives clear information on notable sky events, including details on the most important meteor showers.

The Complete Idiot's Guide to The Sun (2003) by Jay M. Pasachoff
Skywatchers and armchair scientists can learn all about the origin and history of the Sun. With information on the Sun's physical properties; how solar flares, sunspots, and winds on its surface affect Earth's atmosphere and environment; solar and lunar eclipses, transits, and occultations, and early astronomers' discoveries about the Sun, including Galileo, Copernicus, Francis Bailey, and the Mayans. Free download.

Tools and Resources for Sun Calculations and Observations
Astronomical Terms, Daylength-Charts, Moon Phases and Positions, Solar Energy Information, Sun Position (Azimuth and Altitude), Sunrise/Sunset Calculators, Sun Calendars. (link contributed by S. Wahlberg).

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 8.1 million records: Astronomy and Astrophysics, Physics, and arXiv e-prints.

Astrophysics Preprints
The arXiv (pronounced "archive", as if the "X" were the Greek letter Chi) is an archive for electronic preprints of scientific papers in the fields of mathematics, physics, computer science, quantitative biology and statistics that can be accessed via the web. In many fields of mathematics and physics, almost all scientific papers are placed on the arXiv.

Handbook of Space Astronomy and Astrophysics, 2nd Edition, 1990
This is a free online version. A comprehensive compilation of the facts and figures relevant to astronomy and astrophysics. With a vast number of tables, graphs, diagrams, and formulae it also includes a comprehensive index and bibliography, allowing readers to easily find the information they require.

Handbook of Space Astronomy and Astrophysics, 3rd Edition, 2007
This is an updated and expanded version of the handbook above.

Astronomy and Astrophysics Data
Chapter 2 of the 3rd edition (2007) of The Handbook of Astronomy and Astrophysics (searchable 7.2 Mb pdf file).

NASA Astrophysics Data System (ADS) Virtual Library
Free online books relating to astronomy and astrophysics that can be browsed and printed on demand.

Centre de Données Astronomiques de Strasbourg (CDS)
Astronomical databases, catalog services, and more.

Astronomical Data Base (Simbad)
The SIMBAD astronomical database provides basic data, cross-identifications, bibliography and measurements for astronomical objects outside the solar system. SIMBAD can be queried by object name, coordinates and various criteria. Links to some other online services are also provided.

Core List of Astronomy and Physics Journals (2003)
This is a list of highly-used and highly-cited physics and astronomy journals. "Use" is measured largely on paper-journal counts from selective academic research-level libraries.

Ned Wright's Cosmology Tutorial
This website contains a tutorial that goes through the basic principles of Cosmology. It begins by doing a historical review of the discoveries that led to the current theory of how the Universe is. The sections deal with the concepts of homogeneity and isotropy, measuring distances, effects of gravity, geometry of space, horizons and inflation, and finally how projects like COBE provide astronomers with evidence of the mass distribution in our Universe. Edward L. (Ned) Wright is a professor of astronomy at UCLA.

Ned Wright's Cosmological Calculator
A cosmology calculator that computes times and distances as a function of redshift for user-defined cosmological parameters.

Coordinate Conversion and Precession Tool (Chandra X-ray Center)

Modern Telescopes and Instrumentation (Christian Clemens, Max-Plank-Institut fuer Astrophysik, Garching, Germany; in English)

Core List of Astronomy Books (2003)
This list of books in astronomy was intended to assist librarians in building collections. This list also attempts to serve as a resource for researchers and as a guide to teaching faculty in selecting available course readings. It's also a useful guide for amateurs searching for a particular astronomical topic.