M8: The Lagoon NebulaCourse AnnouncementsAssignmentsQuiz 2 HintsThe Doppler EffectThe Doppler EffectThe Doppler EffectMeasuring Velocities with Doppler EffectDoppler in practiceDoppler in practiceMeasuring Velocities with Doppler EffectChapter 4SpectroscopySpectrometerTypes of SpectraTypes of SpectraEmission SpectraEmission SpectraAbsorption SpectraAbsorption SpectraEmission and Absorption SpectraEmission and Absorption SpectraSpectra as compositional detectorsSlide 24Kirchhoff’s LawsAtoms and RadiationAtomic StructureLight as a ParticleThe Energy of PhotonThe Energy of PhotonM8: The Lagoon NebulaCredit: Michael Miller & Jimmy WalkerCourse Announcements•Quiz 2 will take place Monday, 19 September–A few hints today•Error found in Question 16 in Practice Questions for Quiz 2 / Exam 1 –Problem corrected. If you downloaded yesterday or this morning, please download the new version.•Exam 1 will take place Wednesday, 28 Sept.–Will cover Chapters 1 – 4, and perhaps Chapter 5 (inclusion, and how much of, depend on how quickly we get through Chapter 4)AssignmentsReading Assignments•Chapter 4. Sections 4.4 and 4.5[Read for Monday, 19 Sept.]Parallel Lectures•No new parallel lecturesMastering Astronomy•Chapter 3 Homework[Due Monday, 19 Sept. at 11:59 PM EDT]Quiz 2 Hints•Know the difference between prograde (slightly more eastward relative to the stars night after night) and retrograde (slightly more westward relative to the stars night after night) apparent motion of planets.•Do the practice problem set I put on Blackboard.The Doppler EffectHow the frequency (wavelength) of a wave changes with respect to relative motionFamiliar Case: Sound waves from an emergency vehicleTowardWaves get compressedShorter Wavelengths (bluer)AwayWaves get stretchedLonger Wavelengths (redder)Not Moving Case Moving at 70% wave speedWave fronts in stationary caseObject moving to right appears to compress the wave as it is moving in the same direction as the wave.The Doppler Effect•If one is moving toward an object, the wavelengths seem shorter (higher frequency) – “bluer”•If one is moving away from an object, the wavelengths seem longer (lower frequency) – “redder”How the frequency (wavelength) changes with respect to relative motionThe Doppler EffectHow it worksIn this example the object is moving and the observer is not moving.•The Doppler Effect depends on relative motion.•Motion needs to be radial motion (toward/away)•Side-to-side motion (not toward nor away) is called transverse motion–No Doppler EffectNo RelativeMotionObject Moving to RightMeasuring Velocities with Doppler EffectExample: If an object is receding (moving away) at Earth’s orbital velocity of 30 km/s, we can calculate the observed change in wavelength…If that object is giving off a beam of blue light with a wavelength of 400.00 nm, we would measure that light as having a wavelength of 400.04 nm – A tiny, but easily detectable change change in wavelength recession velocitytrue wavelength wave speed=30 km/s= 0.01 percent.300,000 km/s=Doppler in practiceDetermining moving toward or away from EarthConsider a person moving holding a green laser pointer (λ = 532 nm). The case of a non-Doppler shifted wavelength of light is called the rest wavelength) Example 1: You measure the wavelength of the laser to be 530 nm instead of the rest wavelength of 532 nm. Is the person moving toward or away from you?•Answer:Example 2: You measure the wavelength of the laster to be 540 nm instead of the rest wavelength of 532 nm. Is the person moving toward you or away form you?•Answer:Bonus [High difficulty]: How fast would the person have to be moving away from you to shift the color of the laser to red light at 650 nm?•Answer:Doppler in practiceDetermining moving toward or away from EarthConsider a person moving holding a green laser pointer (λ = 532 nm). The case of a non-Doppler shifted wavelength of light is called the rest wavelength) Example 1: You measure the wavelength of the laser to be 530 nm instead of the rest wavelength of 532 nm. Is the person moving toward or away from you?•Answer: Toward you [530 nm < 532 nm => blue-shifted]Example 2: You measure the wavelength of the laster to be 540 nm instead of the rest wavelength of 532 nm. Is the person moving toward you or away form you?•Answer: Away from you [540 nm < 532 nm => red-shifted]Bonus [High difficulty]: How fast would the person have to be moving away from you to shift the color of the laser to red light at 650 nm?•Answer: Recession Vel. = c * (650nm – 532nm)/532nm = 0.22c - or - 66,500 km/sMeasuring Velocities with Doppler EffectSuch small changes might seem insignificant, but it’s how a Radar Gun works, and it is how we detect the motions of stars due to extrasolar planets (Exoplanets)…CHAPTER 4SpectroscopySpectroscopyThe study of the interaction between light and matter•Spectroscopy is the study of the interaction between light (electromagnetic waves) and matter (atoms, molecules, etc.)•This interaction is depends strongly on the type of matter (specific atom or molecule) and the wavelength (or frequency) of light!–So to study it, we take part of the Electromagnetic Spectrum, (i.e., Visible Light) and break it into it’s component wavelengths (colors)•The tool we use to measure the Intensity/Brightness of each wavelength (color) is called a spectrometer–Brightness as a function of wavelength; we saw this with the Blackbody CurveCarbon AtomRed LightWhat happens when they interact?SpectrometerAn instrument to measure how bright each wavelength of light is.The Tool: Spectroscope/Spectrograph/Spectrometer(1)Star, Planet, etc.(2) Focusing Element 1(3)Narrow Slit (4) Dispersion Element(5) Focusing Element 2(6)You don’t need to memorize the parts of a spectrometerIn this case,Blackbody curveTypes of Spectra1. Continuous Spectra–Created by a blackbody: A sufficiently dense object.–e.g., Star, planet, light bulb filament, hunk of iron, very dense gas2. Emission Spectra–Distinct lines of “color” in emission3. Absorption Spectra–Distinct lines of “color” removed (absorbed)A Blackbody Spectrum a continuous spectrumTypes of SpectraEmission and Absorption Spectra and LinesEmission LinesAbsorption Lines(Blackbody)Emission SpectraEmission from a “hot” gasSpectrum from a hot, diffuse (very low density) gasHot, Diffuse GasEmission SpectrumEmission SpectraEvery element has unique
View Full Document
Unlocking...