Electromagnetic Radiation andScientific InstrumentsPTYS 206-2April 1, 2008Announcements• Deep Impact 6 PM Wednesday Night– Pizza, no beer• Watch at home if you can’t watch here. It willbe discussed in class on Thursday• New homework posted todayThe Cassini SpacecraftScientific InstrumentsRadiation• Cameras• Spectrometers(UV, Vis, IR)• Radar• Radio• Laser altimetersFields and Particles• Mass spectrometers• Magnetometers(measures magneticfields)• Langmuir probes(measures electricalcurrents)• Energetic particledetectorsCCD Cameras, from Astronomers to youThe array of CCDs used onthe Sloan Digital Sky SurveyClose-up of a CCD chipSomething bought in WalmartHow CCDs WorkHow It Works: The Charged-Coupled Device, or CCD by Courtney Peterson, Journalof Young InvestigatorsThe image area is divided up into anarray of very small (10µm x 10µm)individual detectors called pixels.Filters Separate light intowavelengthsThe set of filters used on theHubble Space Telescope CameraOptical (Interference)FiltersCassini CameraImaging Science Subsystem (ISS)Narrow Angle Camera (NAC)Actual Photo - basicallya 10 cm focal lengthtelescopeMechanical DiagramRemember the ElectromagneticSpectrumTwo Kinds of LightAll warm bodies emit radiation.We can characterize the radiation from objects asreflected or emitted.Reflected radiation is light that is produced by aanother object (usually the Sun) that then bounces offthe object being studied.Emitted radiation is produced by the object itself, as aconsequence of its temperature. Usually, UV and visible light are reflected radiationand IR light is emitted radiation.Spectrum:1 a band of colors, as seen in a rainbow, produced byseparation of the components of light by their differentdegrees of refraction according to wavelength.•the entire range of wavelengths of electromagnetic radiation.•An image or distribution of components of anyelectromagnetic radiation arranged in a progressive seriesaccording to wavelength.•A similar image or distribution of components of sound,particles, etc., arranged according to such characteristics asfrequency, charge, and energy.2 used to classify something, or suggest that it can beclassified, in terms of its position on a scale between twoextreme or opposite points : the left or the right of the politicalspectrum. a wide range : self-help books are covering a broader andbroader spectrum.The First Spectrometer was a PrismSpectrometersBreaks light into the contributions from variouswavelengths. This is what scientists call a spectrum.Stefan-Boltzmann Law! P ="#T4All objects emit electro-magnetic radiation. Thepower radiated by anobject at temperature T isproportional to the temp-erature to the 4th power.P is the power radiatedσ= 5.67×10-8 W m-2 K-4 isthe Stefan-Boltzmannconstantε is the emissivity, usuallyequal to ~1.Wein’s Law: λ= 0.003/TThe temperature of an objectdetermines the spectrum of itsemitted radiation.High temperatures imply shortwavelengths; lowtemperatures imply longwavelengths.The wavelength at whichmost of the radiation isemitted is inverselyproportional to thetemperature.Wein’s Lawλ = 0.003/Tλ is the wavelength in metersT is the temperature in KelvinsThe lava from this volcano glowsbecause it is hot.Spectrum of Thermal RadiationThe peak of the curve isdetermined by Wein’s law.The area underthe curve isdetermined by theStefan-Boltzmannlaw.The spectrum of radiationfrom warm bodies has acharacteristic shape.Spectrum Variations with TemperatureThe Sun emits visible light.The Spectrum of the Sun.The Sun’s surfacetemperature is 6000K.Thus it emits radiation ata wavelength ofλ= 0.003/6000 metersλ= 5×10-6 metersThis is in the middle ofthe visible spectrumEarth emits IR radiationEarth’s temperature is300K, and thus radiatesat a peak wavelength ofλ = 0.003 / 300 meters,λ = 10x10-6 meters.This is in the infraredregion of the spectrum.Spectra Identify MaterialsEmission featuresAbsorption featuresSpectral Features from TitanAt ultraviolet wavelengthswe see emissionscharacteristic of nitrogenand hydrogenAt visible and near infraredwavelengths we see absorptionfeatures due to methane.Methane = CH4 = swamp gasReflected LightEmitted LightThermal Emissions from Titanidentify numerous
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