This is what the Milky Way actually looks like as shown on the Astronomy Picture of the Day for October 20, 2007. Most of us have rarely never seen it like this because we live in light polluted areas where most stars have become invisible. We are seeing our galaxy from one of the spiral arms looking toward the central cluster of stars. Much of the center is obscured by dust clouds.
The model below shows what the Milky Way galaxy was supposed to look like when I was growing up [from Astronomical Adventures]. It has four large spiral arms and a large central blob of stars. The model is based on our view of other spiral galaxies and on observations that were made from Earth-based telescopes.
Our solar system is located in the Cruz arm. Other models were similar although the names of the arms were different. The basic plan was a spiral with four large arms (Norma, Scutum-Centaurus, Sagittarius and Perseus) projecting outward from a dense circular mass of stars at the center of the galaxy.
This view has been substantially altered over the past few decades. Astronomers now recognize that the Milky Way is a bar galaxy whose central mass of stars forms a bar shape with arms trailing off the ends of the bar. Typical bar galaxies have only two main arms and recent results indicate that our galaxy conforms to this pattern [Two Of The Milky Way's Spiral Arms Go Missing]. The most recent model is shown below. As you can see, two of the four major arms have now disappeared or have been greatly reduced in size and importance.
The galaxy looks very different from the one I learned about as a child. Does anyone know where our solar system is located on the new model?
UPDATE: I replaced the old image (below) with one from Astronomy Picture of the Day from June 6, 2008. It shows where we are in the galaxy.
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