GE 150 Astronomy

1. GE 150 Astronomy Week #9 March 20, 2012

2. Announcements • Homework #6 – Due Now • Solutions posted on Blackboard Vista after class • Solutions to Homework #5 (Gravity) updated • Exam #2 • This Thursday! • Bring #2 Pencil – Scored by Scantron • Includes material up to & including today • Review Lectures, in-class Tutorials, HW answers

3. What is this a picture of ? Find the hottest star(s), how do you know ? Wien’s Law

4. Imagine that you observe the Sun with a telescope in an orbit above the Earth’s atmosphere. Which of the following spectra would you observe by analyzing the sunlight? dark line absorption spectrum bright line emission spectrum continuous spectrum None of the above

5. What physical situation makes this spectrum? Brightness  Wavelength 

6. Kirchhoff's 3rd Law– When the light from a hot dense object passes through a cooler cloud of gas, the atoms within the cooler cloud can absorb particular colors (wavelengths) of light and produce a absorption line spectrum - a series of dark spectral lines among the colors of the rainbow. The type of spectrum given off depends on the objects involved

7. prism Hot/Dense Energy Source Continuous Spectrum

8. prism Hot/Dense Energy Source Cooler, low density cloud of gas Absorption LineSpectrum Atom’s electrons in the cloud are absorbing light, moving electrons to higher orbits: i.e. the cloud removed some of the light

9. What physical situation does a star like the sun present? To produce an absorption spectrum, the Sun must consist of ahot dense core surrounded by a cooler, low density outer atmosphere

10. The Solar Spectrum 5800 K Brightness Spectrum seen through Earth’s Atmosphere

11. All stars produce dark line absorption spectra

12. Tutorial: Analyzing Spectra – p. 69-72 • Work with your partners - not solo! • Read the instructions and questions carefully. • Discuss the concepts and your answers with one another. Take time to understand it now!!!! • Come to a consensus answer you agree on. • If you get stuck or are not sure of your answer, ask another group.

13. The three spectral curves illustrate the energy output versus wavelength for three unknown stars A, B and C. Which of the stars has the highest temperature?

14. Consider the dark line absorption spectra shown below for Star X and Star Z. What can you determine about the color of the two stars?Assume the left of each spectrum corresponds to shorter wavelengths (blue light) and the right of each spectrum corresponds with longer wavelengths (red light). Star X Star Z Star X would appear blue and Star Z would appear red. Star X would appear red and Star Z would appear blue. Both stars would appear the same color. The color of the stars cannot be determined from this information.

15. Consider the dark line absorption spectra shown below for Star X and Star Z. What can you determine about the temperature of the two stars?Assume the left of each spectrum corresponds to shorter wavelengths (blue light) and the right of each spectrum corresponds with longer wavelengths (red light). Star X Star Z Star X has a higher temperature. Star Z has a higher temperature Both stars have the same temperature. The relative temperatures cannot be determined from this information.

16. What can we learn by analyzing starlight? • A star’s temperature • A star’s chemical composition - peak wavelength of the spectral curve - dips in the spectral curve or the lines in the absorption spectrum • A star’s motion

17. The Doppler Effect • Definition:“The change in wavelength (of either light or sound) due to the relative motion between the source and the observer along the line of sight.”

18. Doppler Effect in Sound

19. Astronomers use the Doppler Effect to learn about the radial (along the line of sight) motions of stars, and other astronomical objects

20. Real Life Examples of Doppler Effect • Doppler Radar (for weather) • Airplane radar system • Submarine radar system • Ok, anything with radar • Radar gun, used by Law Enforcement Officers…

21. The Doppler Effect • Definition: “The change in wavelength of radiation (light) due to the relative motion between the source and the observeralong the line of sight.”

22. The Doppler Effect • When something which is giving off light moves towardsorawayfrom you, the wavelength of the emitted light is changed or shifted V=0

23. The Doppler Effect • When the source of light is moving away from the observer the wavelength of the emitted light will appear to increase. We call this a “redshift”. Unshifted

24. The Doppler Effect • When the source of light is moving towards the observer the wavelength of the emitted light will appear to decrease. We call this a “blueshift”. Unshifted

25. The Doppler Effect • Definition: “The change in wavelength of radiation due to relative motion between the source and the observer along the line of sight.”

26. “Along the line of sight” means the Doppler Effect happens only if the object which is emitting light is moving towards you or away from you. An object moving “side to side” or perpendicular, relative to your line of sight, will not experience a Doppler Effect. Unshifted

27. V=0 Astronomy Application

28. Doppler Shifts • Redshift (to longer wavelengths): The source is moving awayfrom the observer • Blueshift (to shorter wavelengths): The source is moving towards the observer Dl = wavelength shift l0= wavelength if source is not moving v = velocity of source c = speed of light

29. Doppler Effect in Light Top – Sun’s Spectrum (unshifted) Bottom – Redshifted galaxy

30. Doppler Effect in Light H alpha λ0=656 nm Δλ = 22 nm 0

31. What can we learn by analyzing starlight? • A star’s temperature • A star’s chemical composition - peak wavelength of the spectral curve - dips in the spectral curve or the lines in the absorption spectrum • A star’s motion - Doppler shift

32. NOT Homework #7Doppler Shift – Ranking TaskDownload from BB VistaNOTE: Due NEVER!Solutions also provided

33. Lecture Tutorial: Doppler Shift p. 73-77 • Work with your partners - not solo! • Read the instructions and questions carefully. • Discuss the concepts and your answers with one another. Take time to understand it now!!!! • Come to a consensus answer you agree on and write complete thoughts into your LT. • If you get stuck or are not sure of your answer, ask another group.

34. The Doppler Effect causes light from a source moving away to: be shifted to shorter wavelengths. be shifted to longer wavelengths. change in velocity. Both a and c above Both b and c above

35. You observe two spectra (shown below) that are both redshifted relative to that of a stationary source of light. Which of the following statements best describes how the sources of light that produced the two spectra were moving? BLUE RED Source A is moving faster than source B. Source B is moving faster than source A. Both sources are moving with the same speed. It is impossible to tell from looking at these spectra. Spectrum A Spectrum B

36. A bright star is moving toward Earth. What would it’s spectrum look like? an absorption spectrum that is redshifted relative to an unmoving star an emission spectrum that is redshifted relative to an unmoving star a continuous spectrum that is blueshifted relative to an unmoving star an absorption spectrum that is blueshifted relative to an unmoving star a continuous spectrum that is redshifted relative to an unmoving star