1. Lecture 3: What the Universe is Made Of Astronomy 5: The Formation and Evolution of the Universe Sandra M. Faber Spring Quarter 2007 UC Santa Cruz

2. Visible light is composed of different wavelengths. Each wavelength is a different color.

3. The electromagnetic spectrum

4. Objects look different in different wavelengths Different wavelengths measure different things Can you guess what wavelength this picture was taken at? Hint: blue is dim, yellow is bright

5. Part of an EM wave frozen in space and time x

6. Animation #1 Propagating EM wave

7. Rough structure of an atom

8. Electron energy levels (orbitals) within an atom are quantized

9. To make an electron jump up, the incoming photon has to have the right energy; when the electron falls down, the same energy photon is emitted Atoms can interact only with photons of particular wavelengths. This set of wavelengths is its “fingerprint.”

10. Animation #2 Absorption and emission of a photon

11. Emission-line spectra from glowing gases of different elements Hydrogen Helium Mercury Uranium

12. The visible-light spectrum of the Sun is wrapped here end to end from red to blue. The dark “lines” are wavelengths that are absorbed by atoms in the Sun’s outer layers. H H Mg Na There are millions of “lines” in the Sun’s spectrum. The strengths of the lines are related to the number of atoms of each element. Modeling these features allows us to measure the Sun’s composition.

13. Emission versus absorption spectra

14. Animation #3 Emission vs. absorption spectrum

15. An emission and absorption spectrum side by side: Sun vs. glowing iron gas in laboratory. The light from both has been passed through the same apparatus. The known iron wavelengths can be used to calibrate the wavelengths of features in the Sun’s spectrum.

16. Each element has its own spectral signature. Nearly all the stable elements have been seen in stellar spectra. This is how we know that the rest of the Universe is made of the same stuff we are.

17. A major recent discovery: color bimodality