Spectra  Chemistry and Doppler Effect Lecture 10

Sun’s Spectrum Sun is not a blackbody Sun 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. Kirchhoff’s Laws

Sun’s average temperature = 6000K Sunspots are about 2000K cooler  appear dark. Sunspot

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

Section 5-7 & 5-8 : Only certain orbits are possible!  discrete (quantized) energy levels Any 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. Other elements are having more electrons than Hydrogen. Each of these electron has its own set of orbits (unique spectral lines). Each of these electron has its own set of orbits (unique spectral lines).

Doppler Effect stationary sourcemoving source

Doppler effect and sonic boom

Doppler Effect The 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 = Wave Light = wave : blue light (high frequency), red light (low frequency) Light = wave : blue light (high frequency), red light (low frequency)

Doppler shift of Stellar spectrum due to unseen planet(s) blue shift : getting closer red shift : getting farther away

First Discovery : 51 Pegasi b

In summary… Important Concepts Kirchhoff’s Laws Spectral lines (discrete energy levels) Spectroscopy and chemical composition Doppler effect Important Terms Emission/absorption lines Continuum emission Redshift Blueshift Chapter/sections covered in this lecture : sections 5-6 through 5-9