The MIT OpenCourseWare program places course materials from a huge number of MIT courses on the web for free download by anyone. Some of the 1.700 courses even include video lectures and demonstrations. Many of the courses have a direct download feature: this is a ZIP-file that contains all the materials structured into folders that follow the on-line web structure for the course. Simply unzip them with „use folder names“ to preserve the folder structure, and you’ve got it all in convenient local form. Of particular interest to astronomy and space enthusiasts are the following courses:
Introduction to Astronomy
Hands-On Astronomy: Observing Stars and Planets
Note that while there are many readings, worksheets, and other materials in PDF or XML form, there is still quite often a text or a book required for assigned readings, and these are not available online.