Lecture8_ch5b - Light The Cosmic Messenger How does light tell us the speed of a distant object The Doppler Effect Doppler Shifts REDSHIFT Hearing

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Unformatted text preview: Light: The Cosmic Messenger How does light tell us the speed of a distant object? The Doppler Effect Doppler Shifts REDSHIFT Hearing the Doppler effect Cause of the Doppler effect BLUESHIFT Moving AWAY Longer wavelengths “Redder” Moving TOWARD Shorter wavelengths “Bluer” Doppler effect for light No moving or moving ACROSS No shift Doppler Effect & Relative Motion V=0 (or across) Wavelength V>0 (away) V>>0 Measuring Redshift is Measuring Velocity V<0 (towards) V<<0 1 Doppler Effect Summary Telescopes Motion to or away from an observer causes a a shift in the observed wavelength of light. Motion towards you -> “blueshift” = shorter wavelengths. Motion away from you -> “redshift” = longer wavelengths Motion across the sky -> no shifts. Size of the wavelength shift measures speed. Advantages over eyes How do telescopes help us learn about the Universe? Bigger is better 1. Larger light-collecting area 2. Better angular resolution • Bigger (more sensitive, more accurate) • Can add cameras, CCDS • Can “see” more of the electromagnetic spectrum 1. Light Collecting Area • Larger is better. • “Size” = diameter = d • Area is proportional to d2 : • 2x diameter means 4x area • 10-meter has 4x more area than a 5-meter 2 2. Angular Resolution • Clarity, accuity. • Units of angles. e.g. 1’ (eye), 0.05” (HST) Resolution Angle ~ Wavelength Diameter Bigger diameter -> Better resolution A star as seen by the Hubble Space Telescope C* D * A* B* Where would you put your large telescope? The Biggest Optical Telescope Keck I and Keck II Mauna Kea. Primary mirror 10 meters in diameter Mauna Kea, Hawaii 3 Basic Telescope Design Basic Telescope Design • Reflecting: mirrors • Refracting: lenses • Reflecting: mirrors • Refracting: lenses • Nearly all telescopes today are reflecting • Nearly all telescopes today are reflecting Basic Telescope Design • Reflecting: mirrors • Refracting: lenses • Nearly all telescopes today are reflecting Why put telescopes in space? Want one? • Buy binoculars first (e.g. 7x35) - you get much more for the same money. • Ignore magnification (sales pitch!) • Notice: aperture size, optical quality, portability. • “Go-to” capability. • Consumer research: Astronomy, Sky & Tel, Mercury. Astronomy clubs. Atmospheric Effects • Light Pollution • Turbulence causes twinkling - blurs images. • High dry places best. • Above atmosphere even better. 4 Turbulence -makes stars “twinkle.” -blurs our view. View from beneath atmosphere Atmospheric Absorption View from Hubble Infrared Telescopes • Atmosphere absorbs X-ray, UV, some infrared (Figure 5.24) Spitzer Infrared observatory detects “ warm” regions in space 5 X-ray Telescopes • Must be in space • Focusing X-rays is like focusing bullets. • “Grazing incidence” mirrors focus the light. Chandra X-ray Observatory observes energetic phenomena. How does technology revolutionize astronomy? Correcting for turbulence: adaptive optics Adaptive Optics Adaptive Optics 6 Radio Telescopes Arecibo Puerto Rico Interferometry Allows small telescopes to work together to obtain the angular resolution of a large telescope. VLA New Mexico Very Large Array (VLA) : 40 km “telescope” MSU’s telescope: SOAR (SOuthern Astrophysics Research Consortium) 12,800 km telescope MSU has 12% of all of the nights (40/year) & built the Spartan IR camera 7 SOAR telescope mirror is 4.1 meters. The SOAR site is dark, high, calm, and dry. Chileʼs Atacama desert 8 ...
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This note was uploaded on 11/13/2011 for the course ISP 205 taught by Professor Donahue during the Fall '08 term at Michigan State University.

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