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Miller's Astronomy 1 lecture notes on Electromagnetic Radiation

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1. 1. Electromagnetic Radiation LACC §4.2, 4.3, 4.5 • Electromagnetic (EM) Radiation as a wave • Electromagnetic (EM) Radiation as a particle • Interactions between EM Radiation (e.g. light) and Matter All we know about objects beyond our solar system comes (almost) solely from examining the radiation (e.g. light) they emit. Wednesday, February 17, 2010 1
2. 2. Electromagnetic Radiation is a wave • EM radiation is pure energy (it has no mass) • EM radiation results from the motion of charged objects • EM radiation travels at the speed of light through a vacuum (and at lesser speeds through matter) • EM radiation is completely described by its frequency, intensity, and direction of travel. Wednesday, February 17, 2010 2
3. 3. Waves: Diffraction If the wavelength is of a If the wavelength does similar size to a gap ... not match the size of then the wave will the gap, then only a little diffract as shown diffraction will occur below. at the edge of the wave. http://www.gcsescience.com/pwav37.htm Wednesday, February 17, 2010 3
4. 4. Waves: Interference http://www.twow.net/ObjText/OtkCaLdQmB.htm Wednesday, February 17, 2010 4
5. 5. Waves: Interference The diffraction pattern of light The same when the beam passes observed on a distant screen through two identical closely when a He-Ne beam passes spaced slits. through a single narrow slit; http://www1.union.edu/newmanj/lasers/Light%20as%20a%20Wave/ light_as_a_wave.htm Wednesday, February 17, 2010 5
6. 6. EM Radiation as a Wave v = fλ v = velocity f = frequency λ = wavelength Q: What is v for light? A: c, the speed of light = 3x108 m/s = 186,400 miles/s http://www.bbemg.ulg.ac.be/UK/2Basis/freqlength.html Wednesday, February 17, 2010 6
7. 7. E.g. Light http://www.uark.edu/ua/pirelli/html/color_freq_wavelength.html Wednesday, February 17, 2010 7
8. 8. Electromagnetic Radiation is a particle • atoms and molecules absorb and emit photons • a photon is a single packet of EM energy Wednesday, February 17, 2010 8
9. 9. Atoms Emit Photons E = hf E = energy h = Plank’s constant f = frequency h = 6.626x10-34 J•s This makes Plank’s constant the smallest(?) constant in physics. http://www.astrosociety.org/education/publications/tnl/35/light3.html Wednesday, February 17, 2010 9
10. 10. Atoms Absorb and Emit Individual Photons http://steve.ﬁles.wordpress.com/2006/03/Absorption%20emission.jpg Wednesday, February 17, 2010 10
11. 11. The EM Spectrum • Credit: Philip Ronan who has given permission to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version. • Download site: Wikipedia: Image:EM spectrum.svg. http://www.nhn.ou.edu/~jeffery/course/c_energy/energyl/lec001.html Wednesday, February 17, 2010 11
12. 12. EM Radiation: Wave or Particle? Waves Particles • interactions between • interactions between waves results in particles result in interference patters collisions • radiate out from a • are “shot” out in source speciﬁc directions • can bend around • travel in straight corners lines • can bend around • are blocked by obstacles obstacles Wednesday, February 17, 2010 12
13. 13. Electromagnetic Radiation LACC §4.2, 4.3, 4.5 • Electromagnetic (EM) Radiation as a wave (v = fλ) • Electromagnetic (EM) Radiation as a particle (i.e. photons, E=hf) • Interactions between EM Radiation (e.g. light) and Matter: absorption/emission of EM radiation by atoms/molecules All we know about objects beyond our solar system comes (almost) solely from examining the radiation (e.g. light) they emit. Wednesday, February 17, 2010 13
14. 14. LACC HW: Franknoi, Morrison, and Wolff, Voyages Through the Universe, 3rd ed. • Ch. 4, pp. 106-107: 11. Choose your answers from: radio | microwave | infrared | visible | ultraviolet | X-ray | gamma ray. Due at the beginning of next week’s ﬁrst class. Wednesday, February 17, 2010 14
15. 15. Spectroscopy LACC §4.2, 4.3, 4.5 • Thermal Spectra: Wien’s Law, Stefan- Boltaman Law • Types of Spectra: there are 3 types of spectra • Spectroscopy: what can it tell us? All we know about objects beyond our solar system comes (almost) solely from examining the electromagnetic radiation (e.g. light) they emit. Wednesday, February 17, 2010 15
16. 16. Thermal Radiation http://astro.unl.edu/classaction/animations/light/meltednail.html Blackbody Curves or Melting http://cse.ssl.berkeley.edu/bmendez/ ay10/2002/notes/pics/bt2lf0612_a.jpg http://astro.unl.edu/classaction/animations/light/bbexplorer.html Blackbody Curves (NAAP) Wednesday, February 17, 2010 16
17. 17. Thermal Radiation T = Temperature λ = peak wavelength Wein’s law http://feps.as.arizona.edu/outreach/bbwein.html Wednesday, February 17, 2010 17
18. 18. Thermal Radiation F= T 4 F = energy ﬂux σ = Stefan-Boltzmann constant T = temperature Stefan-Boltzmann law http://csep10.phys.utk.edu/astr162/lect/light/radiation.html Wednesday, February 17, 2010 18
19. 19. Types of Observed Spectra http://instruct1.cit.cornell.edu/courses/astro101/lectures/images/lec07_04.jpg http://astro.unl.edu/classaction/animations/light/threeviewsspectra.html Three Views Spectrum Demonstrator Wednesday, February 17, 2010 19
20. 20. Atomic Energy Levels of Hydrogen http://www.daviddarling.info/ encyclopedia/H/ hydrogen_spectrum.html http://astro.unl.edu/classaction/animations/light/hydrogenatom.htmlBlackbody Curves (NAAP) Hydrogen Atom Simulator (NAAP) Wednesday, February 17, 2010 20
21. 21. EM Rad. & Space--Our Sun http://www.weasner.com/etx/guests/2004/guests_spectra.html Wednesday, February 17, 2010 21
22. 22. EM Rad. & Space--Orion N. http://mais-ccd-spectroscopy.com/Planetary%20Nebula.htm Wednesday, February 17, 2010 22
23. 23. EM Rad. & Space--M.W. Wednesday, February 17, 2010 23
24. 24. Images vs. Spectra Which is better, the image of an astronomical object, or the spectrum of an astronomical object? What about photometry? Wednesday, February 17, 2010 24
25. 25. Spectroscopy LACC §4.2, 4.3, 4.5 • Types of Spectra: Continuous, Emission Line, Absorption Line • Thermal (or Blackbody) Spectra: Wien’s Law (Temperature), Stefan-Boltaman Law (Power) • Spectroscopy: Temperature, Composition, Doppler Shift, Density All we know about objects beyond our solar system comes (almost) solely from examining the electromagnetic radiation (e.g. light) they emit. Wednesday, February 17, 2010 25
26. 26. LACC HW: Franknoi, Morrison, and Wolff, Voyages Through the Universe, 3rd ed. • Ch. 4, pp. 106-107: 23, 24. • Ch 5: Tutorial Quizzes accessible from: www.brookscole.com/cgi-brookscole/course_products_bc.pl? http:// ﬁd=M20b&product_isbn_issn=9780495017899&discipline_number=19 Due at the beginning of next class period. Wednesday, February 17, 2010 26