1. Observing the Universe
Expanding Universe?
Observing the Universe

2. Can you remember the two pieces of evidence?
Red shift
They have seen it!!!!!
Also remember that the expanding universe is evidence for the Big Bang……Why?

3. Red Shift
When Hubble looked at the absorption spectra of the stars in the galaxies the light was “shifted” towards the red end of the spectrum, a so called red shift
This was the pattern produced from a star
This was the same star but some time later. The lines have moved towards the red end…red shift!

4. The Hubble Constant
The more distant the galaxy, the greater its speed of recession ( recession means moving away)
Speed of recession = Hubble constant x distance

5. Hubble Constant
Hubble worked on this for a while and his constant changed a few times.
Now its accepted to be 72 km/s per Mpc
This means that a galaxy 1Mpc would be moving at a speed of 72 km/s

6. P73 Lesson 7 Hubble’s constant
Calculate the speed of recession of a galaxy that is at a distance of 100 Mpc, if the Hubble constant is 70 km/s per Mpc.
Using the same value of the Hubble constant given in question 1, calculate the distance of a galaxy whose speed of recession is 2000 km/s.
A galaxy lies at a distance of 40 Mpc from Earth. Measurements show its speed of recession is 3000 km/s. What value does this suggest for the Hubble constant?

7. The answers 1) Speed of recession = Hubble constant × distance.
Speed of recession = 70 km/s per Mpc ×100 Mpc = 7000 km/s
2) Distance = speed of recession/Hubble constant = 2000 km/s/70 km/s per Mpc = 29 Mpc
3) Hubble constant = speed of recession/distance = 3000 km/s/40 Mpc = 75 km/s per Mpc