Pillars of Creation in Vis. and InfraredCourse AnnouncementsAssignmentsQuiz 2 HintsQuiz 2 HintsThe Electromagnetic (EM) SpectrumThe Electromagnetic SpectrumAtmospheric OpacityAtmospheric OpacityOrion Nebula – Multi-wavelengthThe Crab Nebula in multiple wavelengthsThermal RadiationThermal RadiationThermal RadiationA BlackbodyA BlackbodyThe Blackbody Spectrum (Curve)Thermal RadiationRadiation Laws: Wein’s LawWein’s LawThe Color of Stars ExplainedThe “Temperature of the Universe”The Radiation LawsThe Radiation LawsThe Radiation LawsThe Radiation LawsThe Radiation LawsRadiation LawsThe Doppler EffectThe Doppler EffectThe Doppler EffectMeasuring Velocities with Doppler EffectMeasuring Velocities with Doppler EffectPillars of Creation in Vis. and InfraredCourse Announcements•Quiz 2 will take place Monday, 19 September–A few hints today•Exam 1 will not take place on Wednesday, 21 September–Exact exam date TBD, but likely to be 28 Sept.AssignmentsReading Assignments•Chapter 4. Sections 4.1 – 4.3[Read for Friday, 16 Sept.]Parallel Lectures•No new parallel lecturesMastering Astronomy•Chapter 3 Homework[Due Monday, 19 Sept. at 11:59 PM EDT]Quiz 2 HintsGuaranteed Questions:•One Force of Gravity Question Change the distance and/or masses, how does the force of gravity change•One Kepler’s 3rd Law QuestionI will give you either the semimajor axis or period, and you must determine the other–You may want to bring a calculator–Example of okay answer (with you showing your work): Given, P = 7 years, you eventually determine that the semimajor axis distance, –Must include unit for full credit!Quiz 2 Hints•Know the definitions for wavelength and frequency of a wave.•Know the pieces of the electromagnetic spectrum in order from longest-to-shortest (or shortest-to-longest) wavelength.•[from Reading] Know the four telescopic observations Galileo made that helped to overturn Geocentrism•There will be one question concerning Seasons from Chapter 1The Electromagnetic (EM) SpectrumMost of the universe is invisible to usNote: Scale is logarithmic, i.e., each labeled tick mark is 10 times the previous- Streteched out to a linear scale, this graphic would stretch many light-years in sizeYou need to know the names of the pieces of the EM Spectrum in the correct order.Visible portion of EM Spectrum very smallThe Electromagnetic SpectrumThe named sub-spectraKnow these in orderLonger Wavelengths Shorter WavelengthsRadio waves Microwaves Infrared Visible Ultraviolet X-rays Gamma RaysAtmospheric OpacityNo one likes a sunburnCredit: NASASpectral WindowsRadioWindowVisibleWindowReaches GroundAbsorbed by atmosphereReaches GroundAbsorbed by atmosphereAtmospheric OpacitySpectral WindowsThe spectral windows are the wavelengths of the EM Spectrum that reach the ground•Determines what light of the universe we can see from Earth’s surface.•The universe looks very different depending on what wavelength (“color”) of light you are observing it in.Credit: NASAOrion Nebula – Multi-wavelengthThe Crab Nebula in multiple wavelengthsCredit: NASA/JPL/ GalileoThermal Radiation•Temperature is a measure of the average microscopic motion•All thermal motions theoretically cease at Absolute Zero–Defined to be 0 Kelvin (0 K)–Not degrees Kelvin!•Kelvin = Degrees Celsius + 273An Absolute Temperature ScaleThermal RadiationBlackbody: An idealized body that absorbs, and reradiates, all wavelengths of light perfectly•Y-axis is Intensity, or simply how much light… the brightness. Larger values, means more of that color•X-axis is either frequency or wavelength•So together, a blackbody spectrum tells how much of each wavelength of light a body with a temperature, T, is giving off (emitting)The Blackbody SpectrumBλ(T)Wavelength versionFrequency versionThe Planck Function-or- Blackbody SpectrumThermal RadiationBlackbody: An idealized body that absorbs, and reradiates, all wavelengths of light perfectly•Characterizes the electromagnetic radiation, or light, emitted by sufficiently dense objects.–Reflects the internal thermal motions (moving particles with charge)–Sufficiently dense covers dense gases, liquids, and solids (e.g., you, a planet, stars, etc.)•As a function of temperature, every temp. has a unique blackbody spectrum (curve)The Blackbody SpectrumBλ(T)Wavelength versionFrequency versionA BlackbodySo what the heck is this imaginary thing called a blackbody?I absorb all light that falls on meAnd reradiate it as thermal radiation according to my temperatureEnergy in(via light)Energy out(via light) as a Blackbody Curve=Light (energy) inLight (energy) inPerfect Thermal Radiation OutPerfect Thermal Radiation OutA BlackbodyEnergy in(via light)Energy out(via light) as a Blackbody Curve=UV Laser(All the same λ)UV Laser(All the same λ)Perfect Thermal Radiation OutPerfect Thermal Radiation OutTotal Energy in is say 100 units of energy per second hitting the blackbody from the UV laserEnergy into blackbody induces thermal motions, which will reradiate according to the temperatureTotal Energy out is also 100 units of energy per second, but now spread out over a lot of wavelengthsWavelengthIntensityWavelengthIntensityThe Blackbody Spectrum (Curve)Characteristics of Blackbody spectra•Every Temperature has a unique blackbody curve associated with it–Different curves NEVER overlap,•According to temperature, each blackbody curve changes in ‘size’ [area under the curve] and location of peak•Area under curve is a measure of total amount of light or energy – depends on (temperature)4•Peak location indicates temperatureBλ(T)Mathematical formulation known as the Planck Function… it’s complicated.UNL Blackbody Curves Simulator provides a useful tool to play with these concepts.Thermal RadiationReality versus IdealBlackbody: An idealized body that absorbs, and reradiates, all wavelengths of light perfectlyIntensityAt top of atmosphereAt sealevelT = 5800 KNote that you can see the spectral windows in the sea level spectrum.The reason for the difference is a topic of Chapter 4 - SpectroscopyRadiation Laws: Wein’s LawPeak of Emission (in wavelength) is inversely proportional to temperature- OR -As Temperature of Blackbody increases the peak in emission decreases to shorter (bluer) wavelengthsin micronsin nanometersThink of intensity as amount of each color (wavelength) the object is emittingIn physics and astronomy, we denote wavelength with the
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