This interactive, online activity traces the history of the telescope from Galileo's first look at the stars to the work of modern observatories. Learners will read about the milestones in telescope development, witness the interplay between technological and scientific advances, glimpse the humanity of the inventors and astronomers behind the telescopes, find out what the telescopes discovered, as well as learn the science of light and optics. Students can work through the activity independently or in groups. Teachers may also choose to have students study a portion of the activity and then share their learning with the class. The science of light and telescopes is presented in the section called "Get to the root of it" that can be used for review, learning the basics, or remediation. Detailed teacher pages, identified as Teaching Tips on the title page of the activity, provide science background information, lesson plan ideas, related resources, and alignment with national education standards.