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1Astro 102/1041Lecture #7: Radiation and Spectra II•How is light absorbed and emitted?–Models of Atomic Structure.Models of Atomic Structure.–Formation of Spectral Lines.Formation of Spectral Lines.–Doppler Shift.Doppler Shift.•Applications in Solar System StudiesApplications in Solar System Studies–Detecting gaseous phases (atmospheres, stars).Detecting gaseous phases (atmospheres, stars).–Detecting solid phases (ices, minerals).Detecting solid phases (ices, minerals).Astro 102/1042The Main PointAstronomers use spectroscopy, the study of the interaction of light and matter, to determine what planetary surfaces and atmospheres are made of.Astro 102/1043How do light and matter interact?•The interaction occurs at the atomicscale.•Therefore, understanding the interaction means understanding the atom.•But the realm of the atom is at a scale that is completely outside our intuitive experience.•So scientists have devised modelsof the atom, to try to grasp what's going on.Astro 102/1044Subatomic Particles•J.J. Thomson discovered the existence of electronsin 1897.•He used a cathode ray tube to show that particles appeared to be carrying negative charge.•Since atoms are neutral, these particles must represent only one part of the atom, whose charge must be balanced by something else.•Wild! Controversial!"Could anything at first sight seemmore impractical than a body whichis so small that its mass is aninsignificant fraction of the mass ofan atom of hydrogen?"-- J.J. Thomson.
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