•Gravity—mutually attractive force between masses•Electromagnetic—electricity and magnetism; binds atoms together•Weak Nuclear—governs nuclear reactions•Strong Nuclear—governs nuclear reactionsThe Four Fundamental ForcesQuestions•What are the properties of light?•How does light interact with atoms?•What are the characteristics of a blackbody?LightLight behaves as particles—photonsOr as an electromagnetic wave (when many photons are present)Fig. 6.5bLight: Particles vs. WavesFig. 6.6Light of different wavelengths makes up the electromagnetic spectrumV I B G Y O RHigher frequency => higher energy photonsThe Electromagnetic SpectrumFig. 6.6Light of different wavelengths makes up the electromagnetic spectrumV I B G Y O RWhere Prof. Glenn worksThe Electromagnetic SpectrumFig. 6.16Because light is a wave, it can be Doppler shifted.This could be a star, for exampleDoppler ShiftIf an object is moving toward an observer, the light is blueshifted. So, how does the frequency of the light change?A) UnchangedB) Higher frequencyC) Lower frequencyConcept Question: Frequency vs. WavelengthFig. 6.12There are two kinds of spectra: continuous and line.Blackbodies have continuous spectra, characteristic of only their temperatures.Fig. 6.131 nm = 10-9m, 1 Angstrom = 10-10mRedBlueYellowBlackbodiesIn what part of the spectrum do human beings emit most of their radiation?A) X-rayB) VisibleC)InfraredD)RadioConcept Question: BlackbodiesFig. 6.1Dispersion of SpectraFig. 6.8Fig. 6.9Atoms (& molecules) produce absorption and emission line spectra.Emission & Absorption Line Spectra from AtomsFig. 6.14Understand this figure!Spectral FormationStars have hot centers that emit continuum radiation and are surrounded by cooler atmospheres. So, which kind of spectra do stars have?A) ContinuumB) Emission lineC)Absorption lineD)Continuum + emission lineE) Continuum + absorption lineConcept Question: Stellar SpectraStars have hot centers that emit continuum radiation that are surrounded by cooler atmospheres. So, which kind of spectra do stars have?Answer:E) Continuum + absorption lineConcept Question: Stellar SpectraFig. 6.17Astronomers use the redshifts of spectral lines to measure the velocities of objects.Redshift and BlueshiftHow Astronomers Plot
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