Astronomy 201

1. Astronomy 201 Classical and Modern Astronomy

2. 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. • Individual Test 2 and Midterm grade discussions at class end. • Extra credit is important for many students. Consider an extra Field Trip! • Tutorials on current topics: Site1Site 2 • But first …

3. Chapter 6 A Some review. Some new.

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

6. 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.

7. 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: becomes 1/22 = ¼, 1/32 = 1/9, 1/42 = 1/16 … • The universe is made of: Space, Energy & Matter • Energy is a key component. • Light is a form of energy with complex properties like wavelength (type) and spectral structure that “fingerprint” its origin.

8. There Are Many Types of Energy • Potential = Energy of Position or Arrangement • Kinetic = Energy of Motion = ½ mV2 • 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 • Mass-energy = often associated with atomic or nuclear processes but not restricted to these cases • And others...

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

11. The Doppler Effect... • …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. • Police radar detectors of speed and TV rain-storm Doppler weather images are based upon the effect.

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15. True Velocity Radial Velocity Tangential Velocity Radar

17. For light: It means a color change.

18. 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 toward the Earth exhibit a blueshift. • These shifts are caused by the Doppler effect.

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

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

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

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

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

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

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

29. Planck’s Law of Black Body Radiation • 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 . • 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.

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

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

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

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

34. 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.

35. 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.

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

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

38. 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

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

42. End of Chapter