McGraw Hill
Arthropods
Are spiders related to crabs? Study the order of arthropods with a reading selection about animal diversity. It provides details about each class within the order, as well as vivid pictures and explanatory charts.
Harvard University
Harvard University: Eye on the Sky, Feet on the Ground
An ebook filled with information and classroom activities covering several astrological topics such as the Earth's rotation and the solar system. Many tips and teaching tools are available to aid in discovering what the sky has to offer.