# Astronomy 201 Classical and Modern Astronomy Week 5 Slide Set 1 TAKE HOME TEST 3 HANDOUT TODAY! T3 & ADLER REPORTS DUE in 3 WKS on April 11. HW5 is due.

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Astronomy 201 Classical and Modern Astronomy

Week 5 Slide Set 1 TAKE HOME TEST 3 HANDOUT TODAY! T3 & ADLER REPORTS DUE in 3 WKS on April 11. HW5 is due April 10. on April 11. HW5 is due April 10. Individual Test 2 and Midterm grade discussions at class end. Individual Test 2 and Midterm grade discussions at class end. Extra credit is important for many students. Consider an extra Field Trip! Extra credit is important for many students. Consider an extra Field Trip! Tutorials on current topics: Site1 Site 2 Tutorials on current topics: Site1 Site 2Site1Site 2Site1Site 2 But first … But first …

Chapter 6 A Some review. Some new.

The Ability to Observe Accurately Is Very Important. You will have 2 seconds to observe the next slide. Look quickly. What do you note?

The Ability to Observe Accurately Is Very Important. What did you see? What is the sign’s important message? –Should we go back? Have you observed Venus or Saturn yourself? Have you observed Jupiter yourself? Have you observed the current phase of the Moon? Do it. Record what you see, when & where seen in the sky. The quiz will have a question.

Recall Some Key Prior Points Gravity is an inverse square law force so, when the distance between the objects is doubled, tripled or quadrupled the force: Gravity is an inverse square law force so, when the distance between the objects is doubled, tripled or quadrupled the force: becomes 1/2 2 = ¼, 1/3 2 = 1/9, 1/4 2 = 1/16 … The universe is made of: Space, Energy & Matter The universe is made of: Space, Energy & Matter Energy is a key component. Energy is a key component. Light is a form of energy with complex properties like wavelength (type) and spectral structure that “fingerprint” its origin. Light is a form of energy with complex properties like wavelength (type) and spectral structure that “fingerprint” its origin.

There Are Many Types of Energy Potential = Energy of Position or Arrangement Potential = Energy of Position or Arrangement Kinetic = Energy of Motion = ½ mV 2 Kinetic = Energy of Motion = ½ mV 2 Radiative = Light (know the 7 types!) Radiative = Light (know the 7 types!) Thermal = Energy of Motion of many small bodies (atoms, molecules, etc.); Higher temperature or more bodies means more thermal energy Thermal = Energy of Motion of many small bodies (atoms, molecules, etc.); Higher temperature or more bodies means more thermal energy Mass-energy = often associated with atomic or nuclear processes but not restricted to these cases Mass-energy = often associated with atomic or nuclear processes but not restricted to these cases And others... And others...

Some Additional Properties of Light That Are Important in Astronomy Doppler Effect Doppler Effect Blackbody Radiation Graph and Blackbody Radiation Graph and Planck’s Explanation Planck’s Explanation Wein’s Law Wein’s Law Stephan-Boltzman’s Law Stephan-Boltzman’s Law

The Doppler Effect... …is the change in wavelength of light due to motion of the source and/or observer of the light. …is the change in wavelength of light due to motion of the source and/or observer of the light. … also occurs in water waves and sound waves. … also occurs in water waves and sound waves. Police radar detectors of speed and TV rain-storm Doppler weather images are based upon the effect. Police radar detectors of speed and TV rain-storm Doppler weather images are based upon the effect.

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For light: It means a color change.

Measuring a Star’s Motion The spectral lines of a star moving away the Earth exhibit a redshift. The spectral lines of a star moving away the Earth exhibit a redshift. The spectral lines of a star moving toward the Earth exhibit a blueshift. The spectral lines of a star moving toward the Earth exhibit a blueshift. These shifts are caused by the Doppler effect. These shifts are caused by the Doppler effect.

Blackbody Radiation a.k.a. “Thermal Radiation” a.k.a. “Thermal Radiation” What is a blackbody? What is a blackbody? an object that is an ideal radiator when hot an object that is an ideal radiator when hot a perfect absorber when cool. a perfect absorber when cool. At normal cool temperatures it appears black. At normal cool temperatures it appears black. Blackbody Examples: Blackbody Examples: light bulb filament light bulb filament stove or fireplace poker stove or fireplace poker stars stars

Star temperatures range from about 3000K to about 50,000K. Star temperatures range from about 3000K to about 50,000K. What has this to do with Blackbody Curves or Graphs? What has this to do with Blackbody Curves or Graphs? The Curves are Intensity versus wavelength plots The Curves are Intensity versus wavelength plots They provide information about a source’s temperature, which relates to its color. They provide information about a source’s temperature, which relates to its color. Look at the following curves. What do you notice? Look at the following curves. What do you notice?

Peak in UV, hot bluish Peak in yellow, cooler yellow-red Peak in IR, coolest red

The North American Nebula: Why is it red? Picture of the Day

Star Colors Reddish  coolest star Reddish  coolest star Orange-ish Orange-ish Yellowish Yellowish White White Bluish  hottest star Bluish  hottest star

3000 K 4000 K 5000 K 6000 K Star Temperatures 10,000 K 15,000 K 30,000 K 7000 K

Josef StefanWilhelm Wien “What happens when things get hotter?” Their brightness changes. Their color changes.

Wien’s Law “Hotter bodies radiate more strongly at shorter wavelengths.” “Hotter bodies radiate more strongly at shorter wavelengths.”

Stefan’s Law “A star’s brightness is proportional to its temperature to the fourth power.” “A star’s brightness is proportional to its temperature to the fourth power.” Light Intensity =  T 4 Light Intensity =  T 4

Planck’s Law of Black Body Radiation In 1901, Max Planck derived a formula for the blackbody curve. In 1901, Max Planck derived a formula for the blackbody curve. The formula in turn can be used to deduce both the Laws of Wein and Stephan & Boltzman. The formula in turn can be used to deduce both the Laws of Wein and Stephan & Boltzman. For his reasoning to work, Planck was inspired to introduce the concept of light as a photon with energy E = hv, where h is a universal constant called Planck’s constant and v is the frequency of the light energy. For this he received the Noble Prize. For his reasoning to work, Planck was inspired to introduce the concept of light as a photon with energy E = hv, where h is a universal constant called Planck’s constant and v is the frequency of the light energy. For this he received the Noble Prize.

Key Points As a star heats up… …its color changes Wien’s Law …and it gets brighter. Stefan-Boltzman’s Law

Thought Question What can you learn from the spectrum of a star? What can you learn from the spectrum of a star? Answers: Answers: Composition Composition Speed Speed Temperature Temperature

Chapter Key Ideas Blackbody Curves Blackbody Curves intensity versus wavelength intensity versus wavelength Consider hot solids, hot gasses and stars. Consider hot solids, hot gasses and stars.

Chapter Key Ideas As a star heats up… As a star heats up… …its color changes …its color changes Wien’s Law Wien’s Law …and it gets brighter. …and it gets brighter. Stefan-Boltzman’s Law Stefan-Boltzman’s Law

Compare these spectra. Spectrum of Hydrogen in Lab Spectrum a Star What do these spectra tell us about the star? Answer: The star is made of hydrogen.

Compare these spectra. Spectrum of Hydrogen in Lab Spectrum a Star What do these spectra tell us about the star? Answer: The star is moving away from us. This is redshift.

Physics Key Ideas for Astronomy Spectroscopy Spectroscopy Kirchhoff’s Laws Kirchhoff’s Laws Bohr Model Bohr Model Protons, Electrons, Neutrons Protons, Electrons, Neutrons Quantized Energy Levels Quantized Energy Levels Emission, Absorption and Ionization Emission, Absorption and Ionization

Waves Transmit Energy and Information This is the only way we know about stars. For example, …

HOT ASTRO NEWS ON MARCH 19. 2008, THEN BRIGHTEST EXPLODING STAR EVER DETECTED! VISIBLE TO NAKED EYE FOR ~30 MIN; BUT NO KNOWN EYEWITNESSES! EXPLOSION TOOK PLACE 7.5 BILLION LY AWAY MEANING THE EXPLOSION TOOK PLACE 7.5 BILLION YEARS AGO

REMEMBER! TAKE HOME TEST 3 HANDOUT TODAY! T3 & ADLER REPORTS DUE: in 3 WKS on April11. HW5 is due April 10. on April11. HW5 is due April 10. Individual Test 2 and Midterm grade discussions at class end. Individual Test 2 and Midterm grade discussions at class end. Extra credit is important for many students. Consider an extra Field Trip! Extra credit is important for many students. Consider an extra Field Trip! Tutorials on current topics: Site1 Site 2 Tutorials on current topics: Site1 Site 2Site1Site 2Site1Site 2

End of Chapter

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