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Starlight - Radiation

Taking Care of Business (TCB). Read textbook Units 23 and 24Homework

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Starlight - Radiation

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    1. Starlight - Radiation

    2. Taking Care of Business (TCB) Read textbook Units 23 and 24 Homework #6 – Friday, October 16 Keep taking Moon observations! Test #2 – Friday, October 16 to Monday October 19 Reserve a test time!!!!

    3. Review Question If you analyze the light from a low density object (such as a cloud of interstellar gas), which type of spectrum do you see? a) dark line absorption spectrum b) bright line emission spectrum c) continuous spectrum

    4. Review Question Imagine that you observe the Sun while in your space ship far above Earth’s atmosphere. Which of the following spectra would you observe by analyzing the sunlight? a) dark line absorption spectrum b) bright line emission spectrum c) continuous spectrum

    5. What physical situation makes this spectrum?

    7. Blackbody For stars/interstellar clouds, photons bounce around inside the object Spectrum depends only on the object’s temperature This is called a blackbody spectrum

    8. Thermal Radiation Rules Rule #1 Hotter objects emit more total radiation per unit surface area This is called the Stefan-Boltzmann Law E = ??T4 Rule #2 Hotter objects emit photons with a higher average energy Temp. doubles=Energy increases by 16

    9. Which object is hotter, an object that is emitting mainly red light or mainly blue light? The blue has a shorter wavelength!

    10. Which object is hotter, an object that is emitting mainly red light or mainly blue light?

    16. Hot objects emit light that PEAKS at short wavelengths (blue). Cool objects emit light that PEAKS at long wavelengths (red)

    17. Wien’s law lpeak = (2.9 x 10-3) / Tkelvin The higher the object’s temperature, the shorter the wavelength of the peak for the light emitted by the object. Temp. decreases=Wavelength increases Temp. increases=Wavelength decreases (shorter wavelength=higher frequency and energy)

    19. What color is our 5800K Sun? The Sun emits all wavelengths of electromagnetic radiation (light); however, the wavelengths of light it emits most intensely are in the green/yellow part of the spectrum.

    23. 1. Which object gives off the greatest amount of Blue light? A, the wavelength is higher (doesn’t matter with the peak) 2. Which object gives off the greatest amount of Red light? A, the curve is higher 3. Which object would appear Red? C, the peak is closer to red 4. Which object would have the lowest temperature? C, the longest wavelengths

    24. Which has the longer peak wavelength? Star A Star C Same

    25. Which star has the lower surface temperature? Star A Star C Same

    26. Which of the two stars looks red? Star A Star C Both Neither, violet

    27. Which star has the greater energy output? Star A Star C Same

    28. Which star is larger? Star A Star C Same

    29. Links to In-Class Problems Go to astro.unl.edu Click on “Class Action” box on right. Light: #7 and #8

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