Dark Matter Is Blowing My Mind!

I'm doing this Physics project where I research an astrological topic and then make a Wiki about it. Well my partner and I chose Dark Matter.

Oops.

Let's see if I can explain.

First, we can tell that galaxies are moving because of something called the Doppler Shift. When light moves toward you, it turns blue (because the light waves scrunch together). When light moves away from you, it turns red (because the light waves stretch out). How much the color shift to red or to blue can tell us how fast the light is moving.

When we look at galaxies, one side is blue and the other is red. That is how we know that galaxies rotate. But when we look closer, we notice something weird. The galaxies appear to be moving much faster than they should be able to given their perceived mass. See, the individual stars are moving so fast that they should be ripping the galaxy apart because they're so light.

But that's not happening.

Right now, the best explanation we have is dark matter. There's something surrounding these galaxies.

Something heavy.

Something invisible.

Something that allows them to move four hundred times faster than they should move on their own.

I don't think I'm going to fall asleep tonight.