GENERAL What's up in the sky? Follow the observing link at Sky & Telescope Powers of Ten Sloan Digitial Sky Survey fly through (see movie at bottom of page) Galileo's leaning tower of Pisa experiment - on the moon: Apollo 15 Famous Thought Experiments Computer Programs Open source planetarium program: Stellarium Astronomical Programs for introductory astronomy by Prof. Hamilton. Build your own solar systems, learn about astronomical distances and giant impacts, practice scientific notation and working with equations, and more! Astronomy Picture of the Day This site is updated daily and has a nice archive of pretty astronomy images. Artificial Satellites: Predictions for artificial satellites H.S. in epicycles The world of Dante AGE AND STRUCTURE OF THE EARTH TimeMapper. Human history timeline. Statigraphy of the Grand Canyon Continental drift animation. The animated poster of Earth as a habitable planet over time. SOLAR SYSTEM Definition of the Astronomical Unit. MESSENGER mission to Mercury. Mars Rover missions: Spirit & Opportunity. Beautiful Mars e-books. Cassini-Huygens mission to explorte Saturn and its rings and moons. NEAR mission to asteroid Eros. Welcome to the Planets Information about planets and spaceprobes from JPL. Deep Impact: Maryland Astronomy's NASA mission to crash into a comet. Comet Crash pictures and movies. Spacewatch This page contains information about this program which searches for near Earth objects. EXOPLANETS Extra Solar Planets Astronomers have discovered planets around other stars. The list lengthens all the time! The interactive tally of exoplanets