Astronomy and Cosmologies Thus.6.May, week 6, Spring 2010, Zita

1. Astronomyand CosmologiesThus.6.May, week 6, Spring 2010, Zita • Brief Q&A • Light and Spectra • Discuss Tuesday workshops • Online spectra workshop • Caper 45 & 53 (half the class do each, then compare) • Caper 57: Black Body Radiation • Telescopes • Post research updates each week

2. Guiding Questions for Ch.5: Light * How can we measure the speed of light? * How do we know that light is an electromagnetic wave? * How is an object’s temperature related to the radiation that it emits? * How is an object’s temperature related to the ENERGY that it emits? (What is the evidence that light has both wave and particle properties?) * How can astronomers detect an object’s chemical composition by studying the light it emits? * How does an object’s motion affect the light we receive from it?

3. Measuring the speed of light Ole Roemer’s astronomical measurements Modern lab measurements based on ca. 1676 Fizeau-Foucault method

4. Light as an electromagnetic wave Energy = hf = hc/l

5. Spectrum of white light Notice the range of visual light is about 400-700 nm (4000–7000 Å) Infrared light has wavelengths longer than 700 nm; Ultraviolet has wavelengths shorter than 400 nm.

6. Spectral lines due to absorption or emission

7. You looked at emission spectra of gases Insights from Tuesday workshop? Questions?

8. Online Spectra Lab: http://www.learner.org/teacherslab/science/light/color/spectra/

9. Caper Labs: A1. Half the class do p.45-48: EM spectrum of light (in small teams) then discuss your results with other teams; A2. Simultaneously, half the class do p.53-56: Luminosity, Temperature, Size (in small teams) then discuss your results with other teams; B. Groups A1 and A2 get together to discuss results C1. Brief lecture on Blackbody radiation C2. Everyone do p.57-60 on Blackbody Radiation (in small teams)

10. Energy & Power of Blackbody Radiation

11. Wien’s law relates l and T l(m) T(K) ≈ 3 x 10-3 where l = the peak wavelength and T = the object’s temperature in Kelvin

12. Quiz question: Wien’s Law: l(m) T(K) ≈ 3 x 10-3 where l = the peak wavelength and T = the object’s temperature in Kelvin

13. Stefan-Boltzman Law relates Energy flux and Temperature: • F = s T4 • Where F = energy flux = Power/Area, • = 5.67 x 10-8 W m-2 K-4 T = the object’s temperature in Kelvin

14. Quiz question: • F = energy flux = power/area = s T4 • = constant, T = temperature in Kelvin

15. Let’s find the Luminosity = Power = Energy/time for a blackbody: (1) Luminosity = Flux * 4pR2, and we also know that (2) Flux = s T4. Plug Flux from (2) into (1) and solve for Luminosity = Now you know how the brightness L of a star depends on its size R and its temperature T.

16. C2. Now you can do the CAPER lab p.57-60 on Blackbody Radiation (in small teams)

17. You already know about the Doppler Effect: The wavelength, or color, is shifted for a moving source, e.g. a galaxy.

18. Doppler Effect causes spectral lines to shift: http://www.astro.virginia.edu/class/oconnell/astr121/im/dopp-shifts-spectra.jpg From Astronomy 121 by Robert O’Connell at University of Virginia

19. Finally, a few words about Telescopes First, you don’t have to take the Ch.6 online quiz on telescopes (except Penelope and Caitlin, since this is your research project). Do take the Ch.5 quiz on light. Two main types of telescopes: Refracting (bending light) and Reflecting

20. Virtually all modern telescopes are reflecting: why?

21. Ground-based telescopes can do great … especially with adaptive optics

22. CCDs = revolutionary light bucket brigades

23. Radio telescopes can see where others can’t

24. Research Updates • Post your research updates on Moodle tomorrow • What have you observed? • How has your hypothesis developed, based on your tests? • State your best understanding concisely • Articulate your outstanding questions clearly • Read the Research Updates of other teams. Give them feedback. • Would you like a Poster-making workshop before the Science Carnival?