Copyright © 2009 Pearson Education, Inc. Chapter 5 Light: The Cosmic MessengerCopyright © 2009 Pearson Education, Inc. IgNobel PrizesChapter 5: Light: The Cosmic Messenger Copyright © 2009 Pearson Education, Inc. 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 questionChapter 5: Light: The Cosmic Messenger Copyright © 2009 Pearson Education, Inc. 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 aboveChapter 5: Light: The Cosmic Messenger Copyright © 2009 Pearson Education, Inc. Blue light has _______ compared to red light. A. shorter wavelength B. longer wavelength C. higher energy photons D. A and C E. None of the aboveChapter 5: Light: The Cosmic Messenger Copyright © 2009 Pearson Education, Inc. What’s the difference in what you see when visible light of different energies enters your eye: A. You see a range of brightness B. You see different colors C. Your eye feels warm or cool D. More energetic light makes you blink E. I get this urge to, …, well never mindChapter 5: Light: The Cosmic Messenger Copyright © 2009 Pearson Education, Inc. In a continuous spectrum, what controls how much energy comes out in different colors (more red or more blue light)? A. What the object is made of B. How hot the object is C. A and B D. None of the above E. Simon Cowell’s egoCopyright © 2009 Pearson Education, Inc. How does light tell us the speed of a distant object? The Doppler EffectCopyright © 2009 Pearson Education, Inc. The Doppler Effect Hearing the Doppler Effect as a Car PassesCopyright © 2009 Pearson Education, Inc. Explaining the Doppler Effect Understanding the Cause of the Doppler EffectCopyright © 2009 Pearson Education, Inc. Same for light The Doppler Effect for Visible LightCopyright © 2009 Pearson Education, Inc. Measuring the Shift • We generally measure the Doppler effect from shifts in the wavelengths of spectral lines. Stationary Moving Away Away Faster Moving Toward Toward FasterCopyright © 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 SpectrumCopyright © 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 EffectCopyright © 2009 Pearson Education, Inc. Thought Question A. It is moving away from me. B. It is moving toward me. C. It has unusually long spectral lines. D. It would never get past Simon Cowell 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?Copyright © 2009 Pearson Education, Inc. Thought Question A. It is moving away from me. B. It is moving toward me. C. It has unusually long spectral lines. 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?Copyright © 2009 Pearson Education, Inc. Measuring Redshift The Doppler Shift of an Emission Line SpectrumCopyright © 2009 Pearson Education, Inc. Measuring Redshift Doppler Shift of Absorption LinesCopyright © 2009 Pearson Education, Inc. Measuring Velocity Determining the Velocity of a Gas CloudCopyright © 2009 Pearson Education, Inc. Measuring Velocity Determining the Velocity of a Cold Cloud of Hydrogen GasCopyright © 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 dingbatCopyright © 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 resolutionCopyright © 2009 Pearson Education, Inc. Bigger is better Light Collecting Area of a ReflectorCopyright © 2009 Pearson Education, Inc. Angular Resolution • The minimum angular separation that the telescope can distinguish Angular Resolution Explained using Approaching Car LightsCopyright © 2009 Pearson Education, Inc. Angular resolution: smaller is better Effect of Mirror Size on Angular ResolutionCopyright © 2009 Pearson Education, Inc. Basic Telescope Design • Refracting: lenses Refracting telescope Yerkes 1-m refractorCopyright © 2009 Pearson Education, Inc. Basic Telescope Design • Reflecting: mirrors • Most research telescopes today are reflecting Reflecting telescope Gemini North 8-mCopyright © 2009 Pearson Education, Inc. Keck I and Keck II Mauna Kea, HawaiiCopyright © 2009 Pearson Education, Inc.Copyright © 2009 Pearson Education,
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