Image Credit: NASA / JPL-Caltech / R. Hurt
Since the dawn of astronomy, humans have been trying to figure their place in the cosmos. These days, we know that our Earth goes around the Sun, which is a pretty normal star. We also know that our sun is one of ten billion stars that make up the Milky Way galaxy, a disk-shaped group of stars all revolving around the center of the Galaxy. That much alone took us until the 1920s to really figure out. But what does the Milky Way galaxy look like, and where are we in that Galaxy? We've slowly figured some things out (like that we are 25,000 light-years from the center of our galaxy, and that our galaxy is a spiral galaxy), but the details have been slow in coming.
This is because it is hard to map our galaxy. Unknown amounts of dust block our view along many lines of sight, and different data sometimes seems to give different answers. It is a lot like trying to figure out the shape of a forest while standing in the middle of it and not being allowed to move. But, at this week's meeting of the American Astronomical Society, a team of astronomers presented a new map of our Milky Way galaxy that represents the best collection of data we have to date.
In this map, (pictured above, but better seen at today's Astronomy Picture of the Day) the spiral Milky Way has lost a couple of spiral arms -- what we thought were a couple of arms are actually partial arm-lets in between the two biggest arms. And this is a good thing. Most spiral galaxies only have two arms, so it seemed strange that ours had three or four. Now we know that our Milky Way is a pretty normal-looking spiral galaxy.
This map may well change in details as we learn more in the future, but it comes a long way from William Herschel's map of the Milky Way just 200 years ago. But, should you ever get lost on an intergalactic cruise, our new map may just be good enough to get you home.