Star Journey - National Geographic
http://www.nationalgeographic.com/stars/
Take a journey in space with the Star Chart. Presents details about the heavens as well as the Hubble Space Telegraph.

StarChild
http://starchild.gsfc.nasa.gov/
NASA learning center for young astronomers, provides guides and activities. Study the solar system, astronauts, solar probes, and space travel.

The Nine Planets
http://seds.lpl.arizona.edu/nineplanets/nineplanets/nineplanets.html
A complete guide to the solar system.

Virtual Solar System - National Geographic
http://www.nationalgeographic.com/solarsystem/
National Geographic takes you on a tour through the solar system, see images of the planets, Sun, and comets up close, and read about each.

Why Do Stars Twinkle While Planets Do Not?
http://www.desy.de/user/projects/Physics/twinkle.html
A small site with information on why stars twinkle and planets don’t.

Why is the Sky Dark at Night?
http://www.arachnoid.com/sky/
Provides clear explanations to the physical phenomena that account for the dark sky. Includes interactive graphs and models.

Windows to the Universe
http://www.windows.umich.edu/
Virtual textbook covers all aspects of human involvement in space and astronomy. Subjects stretch from myths to scientific exploration.

Your Weight on Other Worlds
http://www.exploratorium.edu/ronh/weight/
Use this tool from the Exploratorium to determine what your weight would be on other celestial bodies, including Mars, the Moon and the Sun.

Zoom Astronomy - Enchanted Learning Software
http://www.EnchantedLearning.com/subjects/astronomy/
Interactive guide to the solar system and other regions of space includes a glossary, biographies of astronomers, and quizzes.