Comment Re:Dark? (Score 1) 119
lHow can they possibly tell how much of the matter is "Dark"? I can get the idea of what they're doing - using the relative speeds of each local galaxy to determine the masses contained within each, but how could they possible determine how much mass in each galaxy wouldn't be seen by using light within the bounds of the visible spectrum?
You can see the light. So you do this: 1: Measure the mass of the galaxy. 2: Add up all the mass from the stuff you can see. Subtract (2) from (1).