What does the Rotation Curve of our Galaxy tell us?
Most matter is dark matter
Observations of very Type Ia Supernovae indicate what?
The expansion of the universe is accelerating
Galaxies act like a lens and bend the light of farther galaxies. We can use this to find and measure more dark matter - find total mass of lens
Relates distance and velocities of galaxies
thought to be so distant because they have very large redshifts
-occurred in the first 3 minutes of big bang
-answer to the horizon problem
Hydrogen Spin Flip
-The spiral arms have a lot of neutral hydrogen gas.
-produces a 21cm radio photon
-21cm radio photon=spiral arms
3 Assumptions of Modern Cosmology
-universe is the same everywhere no center or edge.
-General relativity is a complete and true theory of gravity.
-Universality: At all places, at all times, the laws of physics are the same.
Types of Clusters
Irregular: poor, few to few hundred (local group 30)