Dark matter: How does it clarify a star's speed? - Don Lincoln

View full lesson: http://ed.ted.com/lessons/dark-matter-how-does-it-explain-a-star-s-speed-don-lincolnAll the stars in a spiral galaxy rotate around a center -- but to astronomers, the speed that each star travels wasn't making sense. Why didn't stars slow down toward the edges as expected? Don Lincoln explains how a mysterious force called dark matter is (possibly) the answer -- and why the search for an answer matters.Lesson by Don Lincoln, animation by RocknRoll Animation. Learn more about your ad choices. Visit megaphone.fm/adchoices