Astronomy Education Resources - A collection of lesson plans, articles, and resource guides from the Astronomical Society of the Pacific.
CosmoQuest - Participate in astronomy citizen science projects, and explore their 365 Days of Astronomy podcast and blog.
EarthSky Tonight - Information on tonight's astronomical happenings.
GoogleMars - In collaboration with NASA, this site offers close-up views of the regions and geological features of Mars, and the locations of both active and inactive spacecraft on the planet's surface.
Introduction to Astronomy: Crash Course - A series of quick-paced educational videos all about astronomy. Produced by PBS LearningMedia
Jet Propulsion Labratory (JPL) - Information on current and past space missions, a large education page, and links to lots of images, videos, podcasts, and free mobile apps.
JPL Mars Rover - Learn about the current Mars Rover Opportunity, and visit sections for kids, students, and teachers.