Chapter 5 Light The Cosmic Messenger Copyright 2009 Pearson Education Inc IgNobel Prizes Copyright 2009 Pearson Education Inc Chapter 5 Light The Cosmic Messenger How can light behave as both a wave and a particle A It really is both a wave and a particle B Light and small objects such as atoms behave in ways we never see in everyday objects so we can t describe them in everyday terms C This is what quantum mechanics describes D B and C E I bet you Simon Cowell can t answer this question Copyright 2009 Pearson Education Inc Chapter 5 Light The Cosmic Messenger What is the electromagnetic spectrum A Light of all different wavelengths B Light of all different energies C Radiation some of which is dangerous and some of which is harmless D All of the above Copyright 2009 Pearson Education Inc Chapter 5 Light The Cosmic Messenger Blue light has compared to red light A B C D E shorter wavelength longer wavelength higher energy photons A and C None of the above Copyright 2009 Pearson Education Inc Chapter 5 Light The Cosmic Messenger What s the difference in what you see when visible light of different energies enters your eye A B C D E You see a range of brightness You see different colors Your eye feels warm or cool More energetic light makes you blink I get this urge to well never mind Copyright 2009 Pearson Education Inc Chapter 5 Light The Cosmic Messenger In a continuous spectrum what controls how much energy comes out in different colors more red or more blue light A B C D E What the object is made of How hot the object is A and B None of the above Simon Cowell s ego Copyright 2009 Pearson Education Inc How does light tell us the speed of a distant object The Doppler Effect Copyright 2009 Pearson Education Inc The Doppler Effect Hearing the Doppler Effect as a Car Passes Copyright 2009 Pearson Education Inc Explaining the Doppler Effect Understanding the Cause of the Doppler Effect Copyright 2009 Pearson Education Inc Same for light The Doppler Effect for Visible Light Copyright 2009 Pearson Education Inc Measuring the Shift Stationary Moving Away Away Faster Moving Toward Toward Faster We generally measure the Doppler effect from shifts in the wavelengths of spectral lines Copyright 2009 Pearson Education Inc The amount of blue or red shift tells us an object s speed toward or away from us The Doppler Shift of an Emission Line Spectrum Copyright 2009 Pearson Education Inc Doppler shift tells us ONLY about the part of an object s motion toward or away from us How a Star s Motion Causes the Doppler Effect Copyright 2009 Pearson Education Inc Thought Question I measure a line in the lab at 500 7 nm The same line in a star has wavelength 502 8 nm What can I say about this star A B C D It is moving away from me It is moving toward me It has unusually long spectral lines It would never get past Simon Cowell Copyright 2009 Pearson Education Inc Thought Question I measure a line in the lab at 500 7 nm The same line in a star has wavelength 502 8 nm What can I say about this star A It is moving away from me B It is moving toward me C It has unusually long spectral lines Copyright 2009 Pearson Education Inc Measuring Redshift The Doppler Shift of an Emission Line Spectrum Copyright 2009 Pearson Education Inc Measuring Redshift Doppler Shift of Absorption Lines Copyright 2009 Pearson Education Inc Measuring Velocity Determining the Velocity of a Gas Cloud Copyright 2009 Pearson Education Inc Measuring Velocity Determining the Velocity of a Cold Cloud of Hydrogen Gas Copyright 2009 Pearson Education Inc What have we learned What are the three basic types of spectra Continuous spectrum emission line spectrum absorption line spectrum How does light tell us what things are made of Each atom has a unique fingerprint We can determine which atoms something is made of by looking for their fingerprints in the spectrum Copyright 2009 Pearson Education Inc What have we learned How does light tell us the temperatures of planets and stars Nearly all large or dense objects emit a continuous spectrum that depends on temperature The spectrum of that thermal radiation tells us the object s temperature Copyright 2009 Pearson Education Inc What have we learned How does light tell us the speed of a distant object The Doppler effect tells us how fast an object is moving toward or away from us Blueshift objects moving toward us Redshift objects moving away from us Simon Cowell is a total dingbat Copyright 2009 Pearson Education Inc 5 3 Collecting Light with Telescopes Our goals for learning How do telescopes help us learn about the universe Why do we put telescopes into space How is technology revolutionizing astronomy Copyright 2009 Pearson Education Inc How do telescopes help us learn about the universe Telescopes collect more light than our eyes light collecting area Telescopes can see more detail than our eyes angular resolution Telescopes instruments can detect light that is invisible to our eyes e g infrared ultraviolet Copyright 2009 Pearson Education Inc Bigger is better 1 Larger light collecting area 2 Better angular resolution Copyright 2009 Pearson Education Inc Bigger is better Light Collecting Area of a Reflector Copyright 2009 Pearson Education Inc Angular Resolution The minimum angular separation that the telescope can distinguish Angular Resolution Explained using Approaching Car Lights Copyright 2009 Pearson Education Inc Angular resolution smaller is better Effect of Mirror Size on Angular Resolution Copyright 2009 Pearson Education Inc Basic Telescope Design Refracting lenses Refracting telescope Copyright 2009 Pearson Education Inc Yerkes 1 m refractor Basic Telescope Design Reflecting mirrors Most research telescopes today are reflecting Reflecting telescope Copyright 2009 Pearson Education Inc Gemini North 8 m Keck I and Keck II Mauna Kea Hawaii Copyright 2009 Pearson Education Inc Copyright 2009 Pearson Education Inc Mauna Kea Hawaii Copyright 2009 Pearson Education Inc Different designs for different wavelengths of light Radio telescope Arecibo Puerto Rico Copyright 2009 Pearson Education Inc X ray telescope grazing incidence optics Copyright 2009 Pearson Education Inc Want to buy your own telescope Buy binoculars first e g 7 35 you get much more for the same amount of money Ignore magnification sales pitch Notice aperture size optical quality portability Consumer research Astronomy Sky Telescope Mercury magazines astronomy clubs Copyright 2009 Pearson Education Inc Why do we put
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