1. dust 2. Hubble's constant 3. Local Group 4. Dark matter is massive enough to produce a gravitational redshift and gravitational microlensing in light from nearby stars or galaxies. The mass of visible matter also can be compared to the total mass of a galaxy or cluster. This invisible portion of the total mass is called dark matter. 5. In an expanding universe, objects are moving away from Earth, so the light they emit would have a redshift as observed from Earth. In a decelerating universe, light would have no redshift. Light would have a blueshift in a collapsing universe because all objects in that type universe would be moving toward each other. Read more on -