Are We at the Center of the Milky Way Galaxy?

Because we apparently didn't learn our lesson, there was a debate in the early part of this century about the location of the Sun in the Milky Way galaxy. Today, we know that the Milky Way galaxy is a spiral galaxy (e.g., see M100, M51). composed of a few 100 billion stars and that the Sun is roughly 2/3 of the way out in the disk in a spiral arm (see figure). But, how did we deduce the shape of our Galaxy and our position within the Galaxy?

• Herschel (and later, Kapteyn) performed a simple exercise. They counted stars in various directions in the Milky Way galaxy. Their results could be interpreted to indicate that the Sun was near the center of the Milky Way. Oh my!

• Shapley and Trumpler resolved the issue. Essentially, the problem is that dust obscures distant stars. Trumpler came up with this idea and Shapley demonstrated that it was true. How?

The Sun is not at the center of the Milky Way galaxy.

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