What are our units of measure in astronomy? To begin our exploration of astronomy, we first need to develop a common language for notating large numbers, and introduce the basic units of length, mass, and time that we will use throughout the quarter. This lecture is a quick review of scientific notation and the metric system. For measuring the vast distances in astronomy, we need to introduce two special units: the Astronomical Unit for interplanetary distances, and the Light Year for interstellar distances. We end with a discussion of mass and weight, and the distinction drawn in physical measurements that differs (a little) from everyday usage. Recorded 2007 Sep 20 in 1000 McPherson Lab on the Columbus campus of The Ohio State University.