A brief primer on scientific notation, and an on-line test you can take to check your understanding.
A readable explanation of linear and geometric scales (also known as logarithmic scales) as well as an introduction to logarithms. (Note: available as a PDF file only.)
A short guide to calculation with units. Lists conversion factors for units often used in astronomy.
A summary of the Solar System, describing the properties of the major planets as well as the contents of assorted belts of rubble.