Astronomy and Cosmologies Thus 6 May week 6
- Slides: 24
Astronomy and Cosmologies Thus. 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
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?
Measuring the speed of light Ole Roemer’s astronomical measurements ca. 1676 Modern lab measurements based on Fizeau-Foucault method
Light as an electromagnetic wave Energy = hf = hc/l
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.
Spectral lines due to absorption or emission
You looked at emission spectra of gases Insights from Tuesday workshop? Questions?
Online Spectra Lab: http: //www. learner. org/teacherslab/science/light/color/spectra/
Caper Labs: A 1. Half the class do p. 45 -48: EM spectrum of light (in small teams) then discuss your results with other teams; A 2. Simultaneously, half the class do p. 53 -56: Luminosity, Temperature, Size (in small teams) then discuss your results with other teams; B. Groups A 1 and A 2 get together to discuss results C 1. Brief lecture on Blackbody radiation C 2. Everyone do p. 57 -60 on Blackbody Radiation (in small teams)
Energy & Power of Blackbody Radiation
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
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
Stefan-Boltzman Law relates Energy flux and Temperature: F = s T 4 Where F = energy flux = Power/Area, s = 5. 67 x 10 -8 W m-2 K-4 T = the object’s temperature in Kelvin
Quiz question: F = energy flux = power/area = s T 4 s = constant, T = temperature in Kelvin
Let’s find the Luminosity = Power = Energy/time for a blackbody: (1) Luminosity = Flux * 4 p. R 2, and we also know that (2) Flux = s T 4. 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.
C 2. Now you can do the CAPER lab p. 57 -60 on Blackbody Radiation (in small teams)
You already know about the Doppler Effect: The wavelength, or color, is shifted for a moving source, e. g. a galaxy.
Doppler Effect causes spectral lines to shift: http: //www. astro. virginia. edu/class/oconnell/astr 121/im/dopp-shifts-spectra. jpg From Astronomy 121 by Robert O’Connell at University of Virginia
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
Virtually all modern telescopes are reflecting: why?
Ground-based telescopes can do great … especially with adaptive optics
CCDs = revolutionary light bucket brigades
Radio telescopes can see where others can’t
Research Updates 1. 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 2. Read the Research Updates of other teams. Give them feedback. 3. Would you like a Poster-making workshop before the Science Carnival?
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