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The Origin and Nature of Light

The Origin and Nature of Light. Celebration of Knowledge #2 (aka Exam #2) is Thursday March 8th in N210 Tailgate Party (aka exam review) is Wednesday March 7th in N210 from 4-6pm

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The Origin and Nature of Light

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  1. The Origin and Nature of Light • Celebration of Knowledge #2 (aka Exam #2) is Thursday March 8th in N210 • Tailgate Party (aka exam review) is Wednesday March 7th in N210 from 4-6pm • HW #5 – Handed out in class Feb 27th on the topic of Luminosity Area and Temperature, and Due IN-CLASS Tuesday March 6th

  2. HW#6 – Masteringastronomy online homework on Properties of Light and Matter.Available March 1st , Due March 8th by 10am. The Origin and Nature of Light

  3. What physical situation makes this spectrum?

  4. 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

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

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

  7. 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…

  8. 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.”

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

  10. 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”.

  11. 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”.

  12. 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.”

  13. Doppler Effect • “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.

  14. V=0 Astronomy Application

  15. 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 lo = wavelength if source is not moving v = velocity of source c = speed of light

  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 - Doppler shift

  17. Doppler Shift Lecture Tutorial Handout • Work with a partner! • 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 both agree on and write complete thoughts into your LT. • If you get stuck or are not sure of your answer, ask another group.

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

  19. Spectrum A Spectrum B You observe two spectra (shown below) that are 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.

  20. A bright star is moving toward Earth. If you were to look at the spectrum of this star, what would it 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

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