The Milky Way
is a barred-spiral galaxy
approximately 250-300 thousand light-years
in circumference and containing 200-400 billion stars. The Sol
system, containing the planet Earth
, is located in one of the Milky Way's spiral arms.
The Milky Way is often used as a model when estimating interstellar travel distances. For instance, if a trip is described as going from the "core" of a galaxy to the "rim" of the galaxy, the distance can be estimated to be a significant fraction of the 50-60 thousand light-year radius of the Milky Way.
For many science fiction settings (including Star Trek), the Milky Way is the actual galaxy in which events occur, making its features even more relevant to debates involving them.
In Star Trek, Federation maps of the galaxy divide it into four quadrants.