Life in the Universe

Spectra ChemistryandDoppler EffectLecture 10

1Suns SpectrumSun is not a blackbody

Spectrum of the Sun taken above the atmosphere.

Yes, there are so many lines!

Spectral Analysis : Each chemical element produces its own unique pattern of spectral lines.Solar Spectrum

When a chemical substance is heated and vaporized, the spectrum of emitted light exhibits a series of bright spectral lines.Kirchhoff-Bunsen Experiment

Spectroscopy allows to determine the chemical composition of stars and planets!Law 1 : A hot opaque body, such as a perfect blackbody produces a continuous spectrum.

Law 2 : A hot, transparent gas produces an emission line spectrum.

Law 3 : A cool, transparent gas in front of continuum source produces an absorption line spectrum.Kirchhoffs Laws

Suns average temperature = 6000K

Sunspots are about 2000K cooler appear dark.Sunspot

Spectral lines are like fingerprintCarefully examining spectrum, one can deduce chemical composition of an object.Spectroscopy = a systematic study of spectra and spectral lines.Spectroscopy

Section 5-7 & 5-8 : Only certain orbits are possible! discrete (quantized) energy levelsAny orbits are possible continuous energy levels

Hydrogen Atom : allowed orbits for an electron

Light absorption and mission by a Hydrogen atom

Other elements are having more electrons than Hydrogen.Each of these electron has its own set of orbits (unique spectral lines).

Doppler Effect

stationary sourcemoving sourceDoppler effect and sonic boom

Top-Right: THRUST SSC team (fastest car) worlds fastest car (average speed of 660 mph) on Bonneville salt flats in Utah.TA38-Talon trainer super sonic jet13Doppler EffectThe whistle sounds the same no matter where we stand near a stationary train.For a moving train, the sound you hear depends on whether the train is moving toward you or away from you.

Light = WaveLight = wave : blue light (high frequency), red light (low frequency)

Doppler shift of Stellar spectrum due to unseen planet(s)

blue shift : getting closerred shift : getting farther awayFirst Discovery : 51 Pegasi b

In summaryImportant ConceptsKirchhoffs LawsSpectral lines (discrete energy levels)Spectroscopy and chemical composition

Doppler effectImportant TermsEmission/absorption linesContinuum emissionRedshiftBlueshift

Chapter/sections covered in this lecture : sections 5-6 through 5-918