1、Observatories and TelescopesMauna Kea,Hawaii(14,000 ft)Why do telescopes need to be located at high altitude and dry climate?Telescopes Mirrors and Lenses Telescopes are basically a large mirror(reflecting)or a lens(refracting)Consider the human eye as telescope What determines the“power”of a telesc
2、ope?Collecting AreaLensRetinaEye could be a“refracting”telescope,but the size is very smallCollecting Area=Power A=p(d/2)2 ;d diameter Diameter of the telescope indicates its power Largest optical telescope:Keck 1 and 2,each with a mirror of 10 m diameter Large Binocular Telescope(LBT):Ohio State,Ar
3、izona,Germany,Italy Two 8.4 m mirrors in a binocular shaped mount HST Only 2.4 m,but with a huge advantage How much more powerful than HST is the Keck(neglecting that advantage)?New 30m telescope on the drawing boardLarge Binocular TelescopeMount Graham,ArizonaObjective and eyepieceTelescope Objecti
4、ve and Eyepiece The main function of a telescope is to collect as much light as possible from the source,NOT to magnify an image Need bigger and bigger telescopes!The main mirror or lens of a telescope is called the OBJECTIVE The Eye-Piece(small lens or mirror)is to magnify the image after it is for
5、med from the light collected by the objectiveProperties of Light and Telescopes Reflection Mirrors Refraction LensesSimple Refracting TelescopeObjective LensSecondary Lens(Eyepiece)FocusConvex lensSpheres of light from distant source parallel rays at the observerDifferent speeds in different media B
6、ending or RefractionRefraction of light beamLight bends towards the perpendicular going into denser medium,and vice-versa Normal(Perpendicular)Refraction by prism and lensRefractive Index Speed of light slows down in a medium!The ratio of the speed of light in vacuum to the speed in a medium c/v=m m
7、u is called the Refractive Index Material R.I.Water 1.33 Glass 2.6 Bending of light(diffraction)depends on R.I of the medium and wavelength of light lChromatic Aberration:Different colors at different focusChromatic aberration affects refracting telescopes;therefore use reflecting telescopes in mode
8、rn observatoriesLaw of Reflection:Angle i=Angle rPrimaryMirrorPrime FocusSecondary MirrorCassegrain FocusREFLECTING TELESCOPESReflecting Concave MirrorTelescopic ConfigurationsSpherical and Parabolic Mirrors Wavelength range of observatories and telescopes Ground based telescopes can measure -Visibl
9、e(4000-7000 A),-Near-IR(0.7-2 microns),1 mm=10000 A -Radio(1 mm or greater)All other wavelengths blocked out by the atmosphere Space based observatories for Gamma ray,X-ray,UV,and Far-IR astronomyVisible(Optical)and Radio“Windows”in the AtmosphereRadar and Radio Astronomy Radio telescopes(like huge
10、satellite dish)collect radio waves from astronomical objects Radar telescope=Transmitter+Radio Telescope Doppler Radar Transmits radio waves towards an object and collects reflected radio waves;spread in signal shows distance and velocity Largest radio telescope is the Arecibo,1000 ft diameter,in Pu
11、erto Rico Radio TelescopeAracebo Radio Telescope(Puerto Rico)Rotational Speed and Doppler Shift(Line profile broadens on both the blue and red side)Doppler RadarHubble Space TelescopeGround and HST imagesUnresolved ResolvedVisible and IR images of SaturnGamma-Ray View of the SkyEach wavelength band presents a different and mutually complementary viewTelescope and InstrumentsIntensities of Lines in Absorption Spectra:Atoms absorb energyEmission spectra are a set of bright lines:atoms emit energyObserving Planets and MoonsSpectra of Titan(Moon of Saturn):Methane(CH4)
