1ASTR 1040 ASTR 1040 AccelAccelAstroAstro: : Stars & GalaxiesStars & GalaxiesProf. Prof. JuriJuriToomreToomreTA: Nicholas NelsonTA: Nicholas NelsonLecture 4 Lecture 4 ThurThur20 Jan 201120 Jan 2011zeus.colorado.edu/astr1040zeus.colorado.edu/astr1040--toomretoomreTopics for Today Topics for Today ••Basic principles of Basic principles of eyes, camera, telescopeseyes, camera, telescopes••Twinkle and absorption Twinkle and absorption by our atmosphereby our atmosphere••What light gets through, what does notWhat light gets through, what does not••Next lecture: Telescopes in spaceNext lecture: Telescopes in space----and whyand why••ReadReadChap 14Chap 14(Our Star .. the Sun)(Our Star .. the Sun)••SignSign--up for up for Observatory Night #1, this MonObservatory Night #1, this Mon7/8/9pm7/8/9pm••Homework Set # 1 due todayHomework Set # 1 due today••Respond to next discussion Q on Respond to next discussion Q on CULearnCULearn: : ““What What are pros and cons of a lunar observatory?are pros and cons of a lunar observatory?””Clicker Q: Radio WavesClicker Q: Radio Waves••You are listening to a radio station You are listening to a radio station broadcasting at a FM frequency of 97 Mhz. broadcasting at a FM frequency of 97 Mhz. Which is true?Which is true?••A.A.The radio waves from the station have a wavelength of 97 million meters.••B.B.The “radio waves” received by your radio are not light waves, but rather a special kind of sound wave.••C.C.The radio station broadcasts it signal with a power of 97 million watts.••D.D.The radio waves are causing electrons in your radio’s antenna to move up and down 97 million times per second.D.D.RadiosRadios••You are listening to a radio station You are listening to a radio station broadcasting at a frequency of 97 Mhz. broadcasting at a frequency of 97 Mhz. Which is true?Which is true?• D. The radio waves are causing electrons in your radio’s antenna to move up and down 97 million times per second.fcD.D.Wavelength = Speed of light / frequencyWavelength = Speed of light / frequency= 3.0 x 10= 3.0 x 1010 10 cm seccm sec--11/ 9.6 10/ 9.6 1077secsec--11= 312 cm= 312 cmDoppler shifts from Doppler shifts from different portionsdifferent portionsof of star star broaden the broaden the spectral linespectral lineHow does Doppler shift tell us How does Doppler shift tell us the ROTATION RATE of a star?the ROTATION RATE of a star?slowslowfastfastDiscussion of how doDiscussion of how doROTATING STARS yield ROTATING STARS yield DopplerDoppler--broadened broadened spectral emission linesspectral emission lines2Electromagnetic SpectrumElectromagnetic Spectrumgammagamma--rays xrays x--rays ultraviolet rays ultraviolet visiblevisibleinfrared radioinfrared radio1010--16161010+4+4Where are the cell phones?Where are the cell phones?Discussion of CELL PHONEDiscussion of CELL PHONEfrequencies and wavelengths frequencies and wavelengths and what is involved with themand what is involved with them850 MHz 1850 MHz850 MHz 1850 MHzwavelength x frequency = speed of lightwavelength x frequency = speed of lightNow On to TelescopesNow On to TelescopesVLA VLA ––ScicorroScicorro, NM, NMImaging with our EyesImaging with our Eyes••pupilpupil––allows light to enter the eyeallows light to enter the eye••lenslens––focuses light to create an imagefocuses light to create an image••retinaretina––detects the light and generates signals detects the light and generates signals sent to brainsent to brainBending of Light to FocusBending of Light to Focus(Form an Image)(Form an Image)Telescopes and camerasTelescopes and cameraswork much like our eyeswork much like our eyes3Reflection and refraction (bending of light)Reflection and refraction (bending of light)slower speedslower speedof light in glassof light in glassYour digital cameraYour digital camera(CCD detector)(CCD detector)In what ways is an In what ways is an electron orbiting the electron orbiting the nucleus of an atomnucleus of an atomdifferentdifferentfrom a from a planet planet orbiting the Sunorbiting the Sun??••A.A.The central force is electromagnetic (+ and The central force is electromagnetic (+ and --charges attract), not gravitycharges attract), not gravity••B.B.Not all orbits are allowedNot all orbits are allowed––only certain sizes only certain sizes (they are quantized)(they are quantized)••C.C.Because atomic orbits behave differently Because atomic orbits behave differently from from ““regularregular””orbits we call them orbitalsorbits we call them orbitals••D.D.An electron can jump or make a transition An electron can jump or make a transition from one orbital to another from one orbital to another ••E.E.All of the aboveAll of the aboveE.E.Optical Telescopes of Two TypesOptical Telescopes of Two TypesREFRACTORREFRACTOR(LENS)(LENS)REFLECTORREFLECTOR(MIRROR)(MIRROR)Largest Largest RefractorRefractorYerkes 40Yerkes 40””Modern 8 m Telescope ( Modern 8 m Telescope ( ReflectorReflector))GEMINI 8 mGEMINI 8 mMauna Kea, HIMauna Kea, HI4Modern ReflectorsModern Reflectors6.5 m MMT 6.5 m MMT ––Mt. Hopkins, AZMt. Hopkins, AZ8.3 m SUBARU 8.3 m SUBARU ––Mauna Kea, HIMauna Kea, HIDifferent FOCUS arrangements (to get image)Different FOCUS arrangements (to get image)Keck 10 m Twins (Segmented Reflectors)Keck 10 m Twins (Segmented Reflectors)Mauna Kea, HIMauna Kea, HITwin Keck 10 m Twin Keck 10 m TELESCOPESTELESCOPESMauna Kea, HIMauna Kea, HIAnother viewAnother viewProblems in Looking Through Our Problems in Looking Through Our AtmosphereAtmosphere••Many wavelengths are Many wavelengths are absorbedabsorbed(just don(just don’’t make t make it through to surface)it through to surface)••Turbulence in atmosphere distorts lightTurbulence in atmosphere distorts light::––stars appear to stars appear to ““twinkletwinkle””––angular resolution is degradedangular resolution is degraded••ManMan--made light is reflected by air particlesmade light is reflected by air particles, , yielding bright night skyyielding bright night sky––this is this is light pollutionlight pollutionLight PollutionLight Pollution90% of Earth90% of Earth’’s population cannot see the Milky Ways population cannot see the Milky Way5How many light bulbs does it take to How many light bulbs does it take to screw up an astronomer?screw up an