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Doppler Shift Change in frequency of light due to relative motion of the source to the observer Red Shift - changes to lower frequency if source is moving away Blue Shift - changes to higher frequency if source is moving towards Easy to measure even if object very far away. Use Hydrogen lines in astronomy PHYS 162 2
Greenhouse effect in Earth s Atmosphere PHYS 162 3
Climate Change vs Politics DH :: I Don t Get It In 1970s, two environmental problems understood - Freon Ozone depletion, enhanced UV solved - Carbon Dioxide climate change not solved Carter administration started R&D national lab on renewable energy, canceled during Reagan administration. If had proceeded could now have much larger fraction of US energy from renewables, cheaper energy costs for consumers, less reliance on coal/oil, reduced greenhouse effect, possibly fewer wars in Mideast(??) Not done I didn t get it then and still don t PHYS 162 4
Renewable Energy in 2017 Large Scale electric: Quite cheap natural gas (from fracking) with wind turbine competitive (>25% of electricity in Iowa from wind, costs dropped by 40% since 2008 with generated amount 3X larger) Small scale: solar energy cheap (60% drop in costs since 2008) if install on homes ~12% return on investment include taxes. DH home 50% solar and 50% wind for electricity. But most homes in DeKalb get electricity from coal (!). Large current move to community solar Geothermal good source for heat/ac but larger initial investment in older homes PHYS 162 5
New US Electrical Energy 2010-2016 driven by costs PHYS 162 6
Climate Change vs Politics DH :: I Don t Get It Accounting firm Price Waterhouse Cooper 20 years from catastrophe Accounting firm Ernst & Young helps businesses on Global climate change and sustainability issues For insurance companies, climate change is their #1 risk factor for property/casualty losses easy solution: eliminate coal-produced electricity saves money for more than (probably) 98% of Americans while also good for health/climate. But not being done Natural gas, solar, wind, and geothermal all cheaper (and less dangerous). But in many states the coal and coal-driven power industry is able to impede changes, or even force communities to change to using coal-fired plants, while other states (Ca, Ha, NY) are moving towards 100% renewables for electricity, I don t get it PHYS 162 7
Article January 2017 PHYS 162 8
Brightness Luminosity Magnitude Absolute: intrinsic brightness Ex. 25W vs 100W light bulb Apparent: observed brightness depends on absolute brightness and how far away you are PHYS 162 9
Lenses, Mirrors,Telescopes Refraction: light is bent at surface between two media spherical (parabolic) surfaces focus light-collect over large area and gather to small bend angle varies with color/frequency (prism) Glass will bend light Focal point changes with color Convex lens and focal point PHYS 162 10
Reflecting Mirrors All big telescopes made from mirrors easier to make (especially if large up to 10 m). Only one good surface needed same focal point for all frequencies Focal point PHYS 162 11
Reflecting Mirrors PHYS 162 12
Telescope Applications Collect more light. Depends on area of primary lens = p(d/2) 2 d=aperture Eye/camera d eyepiece telescopes are mostly used to collect more light with angular resolution and aperture being crucial criteria. Magnification usually not important. Often put camera at focal point/plane. Can add together light from multiple telescopes Magnify.: Power = (focal length primary) (focal length eyepiece) PHYS 162 13
Light gathering Telescope Quality bigger mirror and/or sensitive electronic cameras can see dim objects < 10-18 unaided eye Angular Resolution (or Vision ) depends on mirror quality. atmospheric turbulence limits to 1 arc second (1/3600 degree). But placing outside atmosphere or using correctable lens surface or digitally correcting can reduce Hubble Space telescope and some on surface have 1/20 arc-second resolution PHYS 162 14
Human Eye Detecting Light (not on tests) cannot easily save information cannot collect light over long lengths of time Photographic Film -long time exposures-move telescope opposite to Earth s rotation -can filter to see different colors 100W lightbulb about 10 20 photons/sec Electronic Devices (CCD, what is in video/digital cameras) -much more sensitive than film (~100,000,000) see single photon. Often run at liquid nitrogen temperature (-196 C or 321 F) -have amount of light versus time (instead of just sum). Can statistically remove effects of atmospheric twinkling or look for rapid variations -data easier to collect, to make available to others, to analyze PHYS 162 15
Vision Good angular resolution allows 2 close objects to be clearly separated. Same as good vision Good resoultion. See 12 objects Bad Resolution 3 times worse. See 3 objects PHYS 162 16
Telescope Quality = Resolution Poor vs Good PHYS 162 17
Good Resolution plus long time exposure deep spaceimages Hubble Space Telescope PHYS 162 18
Maximize Telescope Quality Place at high altitude, away from cities, to aid in reducing atmospheric effects and light pollution (near Equator also good as can see all of the stars N/S) twin 10 m Keck telescopes Mauna Kea Observatory on big island in Hawaii. visible + infrared. At 13,000 ft PHYS 162 19
Maximize Telescope Quality Operate cameras at low temperature (liquid Nitrogen) and calibrate (example: lasers create artificial star twin 10 m Keck telescopes PHYS 162 20
Subaru Telescope Mauna Kea Subaru: 8.2 m mirror $300,000,000 30 m telescope planned. Really 492 1.4 m mirrors. $1,400,000,000 artist sketch PHYS 162 21
Maximize Quantity Surveys Use a modest size telescope with a very good wide angle camera to survey a large part of the sky observe large numbers of galaxies, supernovas, etc though with poorer resolution large data sets Analyze data, find interesting objects, obtain better images at telescopes with better resolutions Pioneered by Fermilab (particle physics has large data sets, invented world wide web) Sloan Digital Sky Survey 2.5m Arizona Dark Energy Survey 4m Chile NIU students involved in both PHYS 162 22
Blanco Telescope Cerro Tololo Chile Located at 7,000 ft and in operation since 1965 by US-Chile collaboration 4 m mirror plus new 640 mega-pixel camera built at Fermilab. NIU students. First data Sept 2012 Dark Energy Survey PHYS 162 23
Radio Telescopes Easy to make large. Atmosphere (including clouds) do not really effect angular resolution is worse as longer wavelength. Improve by making either with large aperture or faking large using many dishes at same time can get similar to visible light Very Large Array. 27 dishes in New Mexico Arecibo Puerto Rico 1000 ft aperture Both in movie Contact PHYS 162 24
Radio Telescopes Very Large Baseline Array and High Sensitivity Array. Spread out over continents Uses modern time information to add together signals and obtain best angular resolution VLA New Mexico PHYS 162 25
South Pole Telescope 10 m diameter, millimeter range (microwaves) Chicago, Berkeley, Illinois, Case Western, Smithsonian, others, and Fermilab for upgrade Primarily studies Cosmic Microwave Radiation, which is leftover from about 1,000,000 years after the Big Bang, and so Dark Energy At south pole as high altitude and very cold which minimizes water vapor PHYS 162 26