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Class Update • D2L Quiz 6 available today; Questions on Test 2 • Observations • Moon Phases • Due Tuesday, Mar. 3 (1 week) 4 observations needed • Friday, Feb. 20 • 8-9:30pm University of Minnesota (Telescopes, Star Gazing & Moon Craters) PRINT VERIFICATION SHEET • No lecture Thu, Feb. 26 for Student Success Day • Please attend • No lab this week (Tuesday or Thursday) • Lab Dimensional Analysis & Significant Figures Quiz Mar. 3 or 5 depending on your lab section & day Doppler Effect and Dark Matter What can you learn from spectra? Temperature (energy) Density (from type of spectra) Composition (from lines) Moving toward or away (Doppler) Speed Demo: Sound Demo: Car horn blaring as it passes Car moving at nearly constant speed Listen to pitch and volume. What changes in the car sound? Does the volume change? Note: The volume DOES increase on approach and decrease on recession. This is NOT the Doppler Effect. What happened to the VOLUME of the horn? 1. sounded louder and louder as the source approached and sounded fainter and fainter as the source receded 2. stayed at a constant loudness as the source approached then dropped to a fainter but constant loudness as the source receded 3. stayed at the same constant loudness throughout the motion 4. varied too much to tell what the volume was doing What changes in the car sound? Does the volume change? YES, but not due to the Doppler Effect. Does the pitch (frequency) change? What happened to the PITCH (frequency) of the horn? 1. became higher and higher as the source approached and became lower and lower as the source receded 2. stayed at a constant high pitch as the source approached and then dropped to a constant lower pitch as the source receded 3. stayed at the same constant pitch throughout the motion 4. stayed at the same pitch except at the moment the source passed 5. varied too much to tell what the pitch was doing Frequency Volume Time Volume of car horn over time Time Frequency of car horn over time Doppler Effect Shift in frequency (wavelength) due to motion of source or observer or both. Used to measure: • Motion toward or away • Speed Side Note: Discovered by Christian Doppler in the mid-1800’s Sydney Harris “I love hearing that lonesome wail of the train whistle as the frequency of the wave changes due to the Doppler Effect.” Visual of waves from moving source: http://www.acs.psu.edu/drussell/Demos/do ppler/doppler.html Drawing waves from moving source Drawing waves… If source is stationary ( ( ( ←wave moves Source ( * ) vsource = 0 ) ) ) ) wave moves→ If source is stationary ( ( ( ←wave moves Source ( * ) vsource = 0 ) ) ) ) wave moves→ If source moves Source ( ( * Longer λ Lower f Red Shift ) ) ) ) ) Shorter λ Higher f Blue Shift If source is stationary ( ( ( Source ( * ) ←wave moves vsource = 0 ) ) ) ) wave moves→ If source moves ( Source ( * ) ) ) ) ) What if source moves faster? ( ( *))))) Stretched more Compressed more Higher speeds Bigger shifts Same results if source or observer or both move Approach Shift to shorter λ Blue shift (moving toward) higher f Recede Shift to longer λ Red shift (moving away) lower f Bigger shift (change) in λ Bigger speed Ex: Earth’s Speed of Revolution or Orbital Velocity Ex: “Earth’s Orbital Speed” Predict: If Earth is at A, will the star’s spectrum be red-shifted or blue-shifted? Moving away Red shifted Ex: “Earth’s Orbital Speed” Standard Emission Spectra for comparison Absorption Spectra lines of star Earth is at “A”, so star is given designation “a” Ex: “Earth’s Orbital Speed” What color are these lines? Violet (bluish) Ex: “Earth’s Orbital Speed” Where is the red end of the spectrum? Ex: “Earth’s Orbital Speed” Blue end of spectrum Red end of spectrum Ex: “Earth’s Orbital Speed” Is “a” red shifted or blue shifted? Is the star (“a”) moving toward or away from Earth when compared to the standard spectra (top)? Ex: “Earth’s Orbital Speed” Red shift Blue shift Moving away from Earth = Red shift Ex: “Earth’s Orbital Speed” Is “b” red shifted or blue shifted? Standard Emission Spectra Standard Emission Spectra Ex: “Earth’s Orbital Speed” Absorption Spectra lines of star Earth is at “B”, so star is given designation “b” Red shift Blue shift Ex: “Earth’s Orbital Speed” Spectrum of element Xo (at rest) Spectrum of star A (at rest) = 546 nm | || | || = 643 nm || From the spectra above, you can conclude that star A 1. Contains the element Xo and only that element 2. Contains the element Xo and at least one more element 3. Does not contain the element Xo 4. There is not enough information to determine the composition Spectrum of element Xo (at rest) Spectrum of star A = 546 nm | || | || = 643 nm || From the spectra above, you can conclude that star A 1. Contains the element Xo and only that element 2. Contains the element Xo and at least one more element 3. Does not contain the element Xo 4. There is not enough information to determine the composition Spectrum of element Xo (at rest) Spectrum of star A = 546 nm | || | || = 643 nm || From the spectra above, you can conclude that Earth and star A 1. Are moving toward each other 2. Are moving away from each other 3. There is not enough information to determine the relative direction of motion of Earth and the star. Blue Shifted or Red Shifted? Moving Away = Red Shifted Spectrum of element Xo (at rest) Spectrum of star A Spectrum of star B = 546 nm | || | || | || = 643 nm || || From the spectra above, you can conclude that 1. Star A is moving faster away from element Xo than star B 2. Star B is moving faster away from element Xo than star A 3. There is not enough information to determine the relative speed of each star to element Xo. Both star A and B are moving away from Xo and are red shifted. Astronomers can calculate the speed from the wavelength difference. Doppler Effect Summary • https://www.youtube.com/watch?v=h4OnB YrbCjY Apply the Doppler Effect to Galaxies What can we learn? http://nssdc.gsfc.nasa.gov/image/astro/hst_ngc4414_9925.jpg Fritz Zwicky – 1930s • Galaxies are moving too fast • Something holding them together • Proposed dark matter to explain galaxy motion http://ned.ipac.caltech.edu/level5/Biviano2/Biviano4_2.html Vera Rubin – 1960s • Galaxies have bright centers • Expect most mass at center • Expect inner stars to move faster and outer stars to move slower • Based on Kepler’s laws of motion • Like solar system http://astro.berkeley.edu/~gmarcy/women/rubin.html http://nssdc.gsfc.nasa.gov/image/astro/hst_ngc4414_9925.jpg Vera Rubin – 1960s • Instead, outer stars orbit about same speed as inner ones (galaxy rotation problem) • Lots of mass far from center • 90% of mass is unseen = Dark Matter Figure 12-11. Horizons by Seeds and Backman Gravitational Lensing – proposed by Einstein and Zwicky http://teacherlink.ed.usu.edu/tlnasa/reference/ImagineDVD/Files/imagine/d ocs/features/news/grav_lens.html Gravitational Lensing – 1980s • Gravity bends light • Creates multiple images or distorts into arcs • Confirms dark matter Bullet Cluster • 2 clusters of galaxies moving apart after colliding • Red: X-rays (colliding gas) • Blue: dark matter (gravitational lensing) http://antwrp.gsfc.nasa.gov/apod/ap080823.html http://www.nasa.gov/mission_pages/hubble/news/dark _matter_ring_feature.html Dark Matter Matter “seen” by its gravitational pull (lensing) • Motions of galaxies within clusters (Zwicky) • Rotation of galaxies (Rubin) • Bending of distant galaxy light by intervening clusters (Gravitational Lensing) • Collision of two clusters of galaxies • Planck spacecraft: about 5% common matter, 25% dark matter, 70% dark energy Dark Matter What is it? We are much more certain what dark matter is NOT than we are what it is. – NASA – not visible matter, not baryons, not antimatter, not black holes Possibly • MACHOs or WIMPS Soudan Underground Mine State Park in Tower-Soudan, MN – neutrino experiments with Fermilab Cosmos: A Spactime Odyssey (2014) with Neil deGrasse Tyson Episode 13: Unafraid of the Dark Journey into the unknown forces of the universe.