2. The Universe is Expanding – Galactic Redshift Recall from waves, that the frequency of a wave can be distorted by relative motion – The Doppler Effect. Light from distant galaxies also exhibit the Doppler Effect

3. Recall the structure of the Atom

7. Absorption and Emission Spectra

8. n=1 (Ground State) n=3 (2 nd excited state) n=2 (1 st excited state) n=4 n=5 n=3  2626252524242 Larger Jump = More Energy = Bluer Wavelength n=6

9. n=1 (Ground State) n=3 (2 nd excited state) n=2 (1 st excited state) n=4 n=5 Photons of all other energies (wavelengths) are ignored and pass on by unabsorbed. n=2  3262625252424 n=6

10. Hydrogen Helium Oxygen Neon Iron

11. The Suns Absorption Spectrum The Suns Absorption Spectrum from 420 – 430 nm. (TOP) The emission spectrum of Iron (Bottom)

12. Galactic Redshift When looking at the spectral lines of distant galaxies, we see a shift in the spectral lines. example Earth Lab Galaxy  R O Y G B I V

13. The Universe is Expanding – Galactic Redshift Recall from waves, that the frequency of a wave can be distorted by relative motion – The Doppler Effect. Light from distant galaxies also exhibit the Doppler Effect

14. Galactic Redshift Using the Doppler Effect – we can state Earth Lab Galaxy  R O Y G B I V

15. Galactic Redshift If v <<< c then … Earth Lab Galaxy  R O Y G B I V PSRT Teacher Note: The derivation can been seen on page 638 IB Book by Paul Ruth

16. Example Problem 1 –The wavelength of a particular spectral line in the star Megrez in the Big Dipper (Ursa Major, aka the Great Bear) is 486.115nm. Laboratory measurements demonstrate that the normal wavelength is 486.113nm. What speed is this star moving relative to the Earth? Earth Lab Galaxy  R O Y G B I V

17. Example Problem 2 –As measured in the laboratory on earth a spectral line of Hydrogen has a wavelength = 656.285 nm. But in the spectrum of the star Vega this line has a wavelength of 656.255nm. Calculate the speed at which Vega is moving relative to Earth. –Is Vega moving towards or away from Earth? Earth Lab Galaxy  R O Y G B I V

18. Classwork Do #7 (speeds only – for now) & 9ab page 541 of Tsokos