1) The universe is expanding (Hubble's Law)
- We can measure galaxy redshifts (velocities)-We know about spectral absorption lines.
-We understand how these lines are redshifted. - We can measure luminosity (brightness) - We can connect luminosity to distance (Super Novae)
How fast do you have to travel to leave the Earth?
Fun with cannons!http://galileoandeinstein.physics.virginia.edu/more_stuff/Applets/newt/newtmtn.html
How fast do you have to travel to leave the Earth?
Kinetic (moving) Energy Potential
Energy (height)
Energy Conservation
How fast do you have to travel to leave the Earth?
Kinetic (moving) Energy Potential
Energy (height)
Energy Conservation
7 miles/s
2) There is more mass in galaxies than can be explained by starlight alone (Dark Matter) -We know the star-mass in galaxies because we can measure binary star system masses and luminosities -We know how fast galaxies are moving -We know the required mass because we understand escape velocities
Summary1) The universe is expanding (Hubble's Law)
- We can measure galaxy redshifts (velocities) - We can measure luminosity (brightness) - We can connect luminosity to distance (Super Novae)2) There is more mass in galaxies than can be explained by starlight alone (Dark Matter) -We know the star-mass in galaxies because we can measure binary star system masses and luminosities -We know how fast galaxies are moving -We know the required mass because we understand escape velocities3) Dark matter is not ordinary matter
-We understand gas dynamics -We can use gravitational lensing to measure mass