Before we can begin our exploration of astronomy, we 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.

We will first re-introduce the basic metric system, explaining how these

units have a physical basis. For measuring lengths in astronomy, we

need to introduce two special units: the Astronomical Unit, which is

used to discuss interplanetary distances, and the Light Year, used for

interstellar distances. We end with a discussion of mass and weight,

and the distinction draw in physical measurements that differs (a

little) from everyday usage. Recorded 2006 Sep 21 in 100 Stillman Hall

on the Columbus campus of The Ohio State University.