Because what happens when your referent changes? Which direction is Mars from Earth? We obviously need a single navigational system that works anywhere in the universe.
Easy! Assuming the earth is the center of the universe, coordinates are 360,360
± the current position of the Earth in the solar system
± the current position of the solar system in the Milky Way.
In the Local Cluster, in the Local Group, in the Virgo Supercluster, in the Local Mesh
Why not?
Because what happens when your referent changes? Which direction is Mars from Earth? We obviously need a single navigational system that works anywhere in the universe.
Mars would be that way I assume
Plus or minus?
Easy! Assuming the earth is the center of the universe, coordinates are 360,360
± the current position of the Earth in the solar system ± the current position of the solar system in the Milky Way. In the Local Cluster, in the Local Group, in the Virgo Supercluster, in the Local Mesh
In order to return, we just go that way:
There is no center of the universe.