Until recently, astronomers believed that from where we sit — some 28,000 light-years out — we were spinning around the center of the Milky Way at about half a million miles per hour.
New observations suggest that we’re traveling much faster — about 600,000 m.p.h. — and that the Milky Way is actually broader and has 50 percent more mass than was previously thought. Astronomers also have recently found evidence of a second major arm of stars spiraling outward from the Milky Way’s central disk.
This is one of the wonderful things about astronomy. Our understanding of the galaxy around us undergoes a significant shift, and the only real change is the new terrain that opens up inside our heads. We don’t experience a physical lurch, because we’re traveling exactly as fast around the center of the Milky Way as we always were. The lurch we experience is our minds catching up to our actual physical speed. We are so exquisitely attuned to our celestial motions that we seem, to ourselves, to be standing still, no matter how our understanding of the universe changes.
These new observations also remind us of a basic problem in understanding the galaxy that we live in. We cannot get a view from outside it. We are essentially blinded to the structure and motions of the Milky Way by the fact that we live within it. We can see how the neighbors live over in Andromeda — the galaxy with which we’ll one day collide — because we can see the whole galaxy in the distance, even with the naked eye on a dark, clear night.
http://www.nytimes.com/2009/01/07/opinion/07wed4.html?th&emc=th
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