Expert: James Gort - 4/25/2010

Question
How do we know what the milky way galaxy actually looks like?  Are the images we have of it only extrapolations based the locations of visible stars?

Answer
Hi Eric,

Since we're inside the Milky Way, the only way we "know" what it looks like is by mapping the stars and dust in various wavelengths - the visible, infrared, microwave, radio, etc.  We can get a pretty good idea of the structure that way, although some parts are hidden by dust bands.  But even the structure of that dust, and the movement of stars themselves, offer clues.  We can estimate the size of the galaxy and the number of stars that way.  Finally, we can compare what we come up with with the structure of nearby galaxies, and this rounds out the picture.  We don't know exactly what our galaxy looks like, but we think we have a pretty good idea.

Hope that helps.

Prof. James Gort