How can we make any sense of this background?  If you look up at the sky and say "There's Lynx", you need a way to tell someone where in the sky Lynx is (other than pointing with your finger).

We first need to define a coordinate system.  That coordinate system has to have an origin.  We can then define the location of any object in the sky with respect to that origin.

Click on the link below to develop an understanding of how a coordinate system was created, and how to use it.