Deepsky Atlas
Hawaiian Astronomical Society's Storybook and Deepsky Atlas
http://www.hawastsoc.org/deepsky - Details

Hubble Space Telescope
NewsCenter is the complete collection of every Hubble Space Telescope news release and its supporting materials, along with tools and resources designed to further your knowledge of astronomy.
http://hubblesite.org/newscenter/ - Details

John Bortle's Dark Sky Scale
John Bortle created a new scale of sky darkness which he published in the February 2001 issue of Sky and Telescope.
http://www.frostydrew.org/observatory/columns/essays/bortle.htm - Details

Skymaps
Skymaps.com
http://www.skymaps.com/ - Details

messier45
Messier45.com constitutes a non-commercial effort to provide the deep sky observer's most valuable tools online; the map and the lists of objects. Great effort is made to make accurate data accessible to both the novice and experienced observer. There is absolutely no cost for you to use Messier45.com, but if you find this service valuable, please consider making a donation to help me pay for the server expenses etc.
http://messier45.com/ - Details

StarGazer
StarGazer Java atlas
http://www.oras.org/stargazer/applet.html - Details

Weather Underground Sky Chart
Weather Underground Sky Chart
http://www.wunderground.com/sky/index.asp - Details

Sky andTelescope
Sky andTelescope Interactive Sky Chart
http://skyandtelescope.com/observing/skychart/ - Details

Astronomy Picture of the Day
Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
http://antwrp.gsfc.nasa.gov/apod/astropix.html - Details

Deep Sky Database
Create observing lists using the SAC database This site is an online observing list generator for amateur astronomers who love to pursue deep sky objects. It employs a web-based version of the Saguaro Astronomy Club's database (ver 7.2), consisting of over 10,000 records. This online version of the SAC database allows amateur astronomers to compile detailed and customized observing lists. Each search screen has instructions on conducting a useful search along with a link to the Database Documention which will open up in a new window for easy reference. Results can be printed in portrait format with left and right margins set to the minimum (click on File, Page Setup in Firefox or Internet Explorer). Both Firefox and Internet Explorer users will also be able to copy and paste the results directly into Excel, Word, Notepad or Open Office Calc if desired.
http://www.virtualcolony.com/sac/ - Details

Astronomy Pictures
Come and visit a totally unique archive of space photography. Find astrophotographs of galaxies, nebulas, globular cluster, the moon, and the planets of the solar system
http://www.telescopes.cc/ - Details

AstroImage
AstroImage
http://org.utu.fi/yhd/ursa/astroimage.html - Details

The Virtual Amateur Astronomer
The images of nebulae, galaxies, the planets and other astrophysical objects in an amateur telescope cannot compete with the high quality images now available on the Internet. All one needs is a broad-band connection and a guide to the best astronomical photos on the Web. You need to obtain the former, but Jupiter Scientific, through its Virtual Amateur Astronomer® websubsite, provides the latter. Explore the Universe virtually through the power of the Internet!
http://www.jupiterscientific.org/virtualastronomer/ - Details

Constellations
The Constellations and their Stars
http://www.astro.wisc.edu/~dolan/constellations/ - Details

Sky View
Sky View Caf eacute;
http://www.skyviewcafe.com/ - Details

SkyView
SkyView is a Virtual Observatory on the Net generating images of any part of the sky at wavelengths in all regimes from Radio to Gamma-Ray.
http://skyview.gsfc.nasa.gov/ - Details

Heavens Above
Heavens Above
http://www.heavens-above.com/ - Details

National Geographic's
National Geographic's Star Chart
http://www.nationalgeographic.com/features/97/stars/chart/index.html - Details

Estimating Limiting Magnitude
Limiting magnitude is used to evaluate the quality of observing conditions. It tells the magnitude of the faintest star visible to the unaided eye. The limiting magnitude could also be observed by some instrument. It describes well the sky's transparency: better transparency means that fainter stars are visible.
http://obs.nineplanets.org/lm/rjm.html - Details

NASA's Mars Pathfinder Mission
The Mars Exploration Program Since our first close-up picture of Mars in 1965, spacecraft voyages to the Red Planet have revealed a world strangely familiar, yet different enough to challenge our perceptions of what makes a planet work. Every time we feel close to understanding Mars, new discoveries send us straight back to the drawing board to revise existing theories.
http://mpfwww.jpl.nasa.gov/ - Details