Where are we? Where is someplace else? How do I get from here to

there? These are questions we need to answer both on the Earth and in

the Sky to assign a location to a place or celestial object on the

surface of a sphere. We start by introducing angular units, and use

them to describe the terrestrial system of latitude and longitude on the

spherical Earth. We then define the Celestial Sphere, with its

Celestial Equator and Poles, and begin to define an analogous coordinate

system on the sky. An important wrinkle is that what part of the sky we

see at any given time depends on both where we are on the Earth, and

what date/time it is. This gives us the start of the coordinate system

we need to begin our exploration of motions in the sky in the next

lectures. Recorded 2006 Sep 26 in 100 Stillman Hall on the Columbus

campus of The Ohio State University.