Transcript Starlight
Doppler Shift October 19, 2009 Taking Care of Business (TCB) Read textbook Units 25 and 26 No Homework next week! Moon Observations – Monday, October 26 Need total of 9 observations, all columns filled. Test #2 – Friday, October 16 to Monday October 19 Reserve a test time!!!! What can we learn by analyzing starlight? • A star’s temperature - peak wavelength of the spectral curve • A star’s chemical composition - dips in the spectral curve or the lines in the absorption spectrum • A star’s motion •Moving towards us/ moving away •How fast the star is going The Doppler Effect • Definition: “The change in wavelength of radiation (light) due to the relative motion between the source and the observer along the line of sight.” Astronomers use the Doppler Effect to learn about the radial (along the line of sight) motions of stars, and other astronomical objects. On a boat, in the front you can see shorter waves Boat, in the back the waves are longer Real Life Examples of Doppler Effect (Sound or Light) • Sound, NOT the volume of the sound, it’s a build of sound waves (pitch change) • Trains, airplanes, moving vehicles, police sirens, bats • Car headlights, radar gun Doppler Effect • When something which is giving off light moves towards or away from you, the wavelength of the emitted light is changed or shifted V=0 Doppler Effect • When something which is giving off light moves towards or away from you, the wavelength of the emitted light is changed or shifted V=0 longer shorter Doppler Effect • When the source of light is moving away from the observer the wavelength of the emitted light will appear to increase. We call this a “redshift”. Red because the wave length is the longest. Doppler Effect • When the source of light is moving towards the observer the wavelength of the emitted light will appear to decrease. We call this a “blueshift”. Blue, shifted towards the blue Astronomy Application V=0 Doppler Shifts • Redshift (to longer wavelengths): The source is moving away from the observer • Blueshift (to shorter wavelengths): The source is moving towards the observer Dl v l0 c (700-400)/700 = V/3x10^8 m/s V= 34% C Dl = wavelength shift lo = wavelength if source is not moving, 700 nm v = velocity of source c = speed of light The Doppler Effect causes light from a source moving away to: 1. be shifted to shorter wavelengths. 2. be shifted to longer wavelengths. 3. change in velocity. (In space, light will travel in a constant speed.) 4. Both a and c above 5. Both b and c above You observe two spectra (shown below) that are redshifted relative to that of a stationary source of light. Which of the following statements best describes how the sources of light that produced the two spectra were moving? BLUE RED Spectrum A Spectrum B 1. Source A is moving faster than source B. 2. Source B is moving faster than source A., we are told it is redshifted! 3. Both sources are moving with the same speed. 4. It is impossible to tell from looking at these spectra. A bright star is moving toward Earth. If you were to look at the spectrum of this star, what would it look like? 1. an absorption spectrum that is redshifted relative to an unmoving star 2. an emission spectrum that is redshifted relative to an unmoving star 3. a continuous spectrum that is blueshifted relative to an unmoving star 4. an absorption spectrum that is blueshifted relative to an unmoving star, blueshifted (moving towards us), absorption 5. a continuous spectrum that is redshifted relative to an Links to In-Class Problems Go to astro.unl.edu Click on “Class Action” box on right. Light: #11, #12, #13