What are we looking at when we look at the Milky Way?
How many arms are we looking through when we look in each direction?
Our understanding of the Milky Way has been updated recently.
See:
http://www.skyandtelescope.com/news/19599619.html
For more detail see:
http://www.nasa.gov/mission_pages/sp...20080603a.html
When we look towards the center of our galaxy we are looking through 4 arms. The center is 26,000 light years away.
When we look in the other direction we are looking through 3 arms, our arm - the Orion Spur, the Perseus Arm and the Outer Arm.
The edge is 24,000 light years away.
A detailed picture is here:
http://www.nasa.gov/images/content/2...-annotated.jpg