lecture06

lecture06 - Astronomy 3: The Nature of the Universe...

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Astronomy 3: The Nature of the Universe Professor Alice Shapley Lecture 6: Light and Telescopes, contd. The Solar System (NGC 1499 Image credit: Markus Noller, Deep Sky Images)
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Logistics • Quiz #2: due Monday, April 18 th , 10 pm. • Available at CCLE website:
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Logistics Midterm #1 , next Thursday, April 21 st , in class. The midterm will take place in the regular lecture hall, Math Sciences 4000A -- i.e., this room. Most important : bring a photo ID and a #2 (i.e. normal) pencil. Recommended: bring a calculator (though you may not need it). I will provide scantrons. Review session : Monday, April 18 th , 3-5 pm, also in Math Sciences 4000A. Stay tuned for details about 2 nd review session.
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Logistics Exam will have a mixture of multiple choice, matching, and true/false. Exam will be based on the course material up through and including “Light and Telescopes.” This corresponds to lectures 1-5 and the first part of lecture 6 (today). The relevant reading from the textbook is: Chapters 1-6. A few questions will be based on Labs 1-3.
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Review from Last Time Newton’s law of gravitation: orbits, an explanation for Kepler’s laws, and a way to “weigh” objects by the orbits of lighter things around them. Nature of light (wave, particle), the electromagnetic spectrum. Nature of matter on atomic scales. What do we learn from light (i.e. spectra)? 1. Composition of matter 2. Temperature of matter 3. Motion of matter (along the line of sight)
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What types of light spectra can we observe? A plot of Energy versus Wavelength is a spectral energy distribution, or simply a spectrum.
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The unique Energy Levels for Hydrogen. When an electron in an atom absorbs the energy of a photon it moves to a higher energy level. When an electron drops to a lower level it emits a photon of a precise wavelength (= hc/E).
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Two Properties of Thermal Radiation: 1. Hotter objects emit more light at all frequencies per unit area . 2. Hotter objects emit photons with a higher average energy. These curves have a precise mathematical shape that depends only on the absolute temperature. Per area
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Rules for Thermal Radiation Two Laws of Physics: Stefan-Boltzmann: Emitted Intensity per square meter = constant × T 4 Wien’s Law : Wavelength of maximum emission = constant/ T
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How does light tell us the speed of a distant object? The Doppler Effect.
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lecture06 - Astronomy 3: The Nature of the Universe...

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