Measuring parallax and angular diameters are two indirect methods of measuring size and distance in the solar system. The scale model is another indirect method of measurement that also allows us to explore the relationships between multiple components in a system.

This Reading provides background information on the underlying concepts in the Activities included in the book, Project Earth Science: Astronomy, Revised 2nd Edition. The Readings go beyond what is found in the background information in the Activities. They can be used as supplementary information for the teacher, or to enhance classroom discussions.