This video "Light on Dark Matter" by Patricia Burchat is an explanation on the mysteries of the universe; dark matter and dark energy. In this video Patricia explains that ordinary matter (humans, planet, stars etc) make up only 4% of the universe. 26% is made up of dark matter and the rest (70%) is made up of dark energy. Surrounding a galaxy and surrounding a cluster of galaxies is a gravitational force called dark matter. It is a cloud that has mass. Light is involved in this concept as well. When looking at a galaxy, through a telescope or naked eye, you may be seeing it in a different place than it actually is. This could be because a clump of dark matter is obstructing your view. The light from the galaxy is bouncing around this matter and entering your eye at a different angle. Therefore we may see the galaxy in a different place than where it actually is!
Space is growing bigger and bigger. The distance between galaxies is getting greater. Instead of expanding at a slower rate, the rate is actually increasing. The universe is expanding at faster rate than it did billions of years ago. Dark matter pulls matter further apart and encourages expansion. Dark energy decreases gravitational pull and puts more space between the galaxies.