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Light and Telescopes Astronomy 1 — Elementary Astronomy LA Mission College Spring F2015 Quotes & Cartoon of the Day “We find them smaller and fainter, in constantly increasing numbers, and we know that we are reaching into space, farther and farther, until, with the faintest nebulae that can be detected with the greatest telescopes, we arrive at the frontier of the known universe.” Edwin Powell Hubble Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Announcements Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Last Class • • • • History Galileo, Newton (right?) Gravity & Tides Intro to light LT EM Spectrum Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 This Class • • • • LT EM Spectrum Telescopes & Observatories Light and the Atmosphere Multi-wavelength Astronomy Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Electromagnetic Spectrum Astronomy 1 — Elementary Astronomy LA Mission College Spring F2015 The Electromagnetic Spectrum • • All these are the same thing as visible light • Radio waves -- lowest frequency, longest wavelength, least energy per photon Gamma rays -- highest frequency, shortest wavelength, greatest energy per photon Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 WARMUP QUESTION Which of the following has the shortest wavelength? A. A photon of ultraviolet light. B. Blue electromagnetic radiation. C. An X-ray. D. A radio wave. E. Infrared radiation. Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 LECTURE-TUTORIAL EM SPECTRUM P. 47-49 Which of the following has the shortest wavelength? A. A photon of ultraviolet light. B. Blue electromagnetic radiation. C. An X-ray. D. A radio wave. E. Infrared radiation. Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Let’s Practice Consider green light with a wavelength of 550 nm (0.00000055 cm). Light with a wavelength 1000 times longer than this is most likely to be _____. A. Infrared B. Ultraviolet C. Gamma Ray D. Radio (excluding microwave) Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Consider Xrays with frequency 1017 Hz. Light with a frequency one millionth of this (i.e. 1011 Hz) is most likely to be _____. A. Ultraviolet B. Gamma Ray C. Microwave Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Evil aliens have kidnapped you and placed you in chamber with a light source. There is a large dial in front of you marked “wavelength”. It’s currently flooding the room with light and the dial reads 10-12 m. Which way do you turn the dial? A. Toward larger numbers -- fast! B. Toward smaller numbers -- fast! C. I leave it where it is. Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 WAVE- PARTICLE DUALITY Light behaves like both wave and particle • A wave is disturbance or oscillation (of a physical quantity), that travels through matter or space, accompanied by a transfer of energy • • • • example: water waves, sound waves characterized by wavelength, frequency, speed key property is interference A particle in the physical sciences is a small localized object to which can be ascribed physical properties. • • example: bullets, pebbles, sand grains, electrons, protons • • particles do not display interference characterized by size, shape, speed,specific amount of energy, mass, etc. key property is the photoelectric effect Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 The Original Double-slit Experiment Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Particles Waving Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Light behaves like both wave and particle • Light displays interference • • • Double-slit experiment Wave behavior Light deposits energy in discrete (quantized) amounts • • depending only on wavelength • The “particle of light” or “quantum of light” is called a photon • Particle behavior photoelectric effect Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Telescopes and Observatories Astronomy 1 — Elementary Astronomy LA Mission College Spring F2015 Manipulating Light • We commonly use lenses and mirrors to manipulate light in the visible part of the spectrum • all electromagnetic radiation follows the same basic “rules” when it comes to how they interact with matter. • • A radio dish is basically a mirror for radio waves. Telescopes can use lenses, mirrors or a combination of both to collect and focus light Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 TELESCOPES What do you think? • Why do Astronomers use Telescopes? Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Why do Astronomers Use Telescopes? • To gather the faint light from distant objects • • • This is the most important property of a telescope! To resolve details of these objects • • The bigger the telescope, the more light it gathers By creating a detailed image Magnification is relatively unimportant, but the image may be magnified for viewing or for optimal capture of a digital image, etc Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 There are two main types of telescopes • Refractors • • Think Pirate’s Spyglass • Refractors have a large lens or lenses, normally at the front of the telescope, which are the primary optical component Galileo’s Telescopes were Refractors Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 There are two main types of telescopes • Reflectors • • Most modern telescopes are reflectors -- also called Newtonians • including the Hubble Space Telescope Reflectors have a large mirror at the back of the telescope, which is the primary optical component http://www.company7.com/orion/graphics/ Atlas10wManAtEyepc353500.jpg Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Terminology • The “main” lens or mirror is called the Primary or Objective • In reflecting telescopes there is second mirror, to re-direct the light path. This is called the Secondary Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Chrmomatic Aberration • Light slows down in glass • • • returns to c on exit Causes it to bend Violet light bends/slows more than red light • Lenses cause colored fringes called chromatic aberration • effect can be minimized, but not eliminated Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Refractors vs. Reflectors • • • Refractors Advantages Rugged Sealed Tube Relatively Simple design • • • • • • • Disadvantages Chromatic Aberration Heavy Difficult to make glass optically perfect Astronomy 1 - Elementary Astronomy • Reflectors Advantages Can be made very large Glass does not have to be optically perfect Can be made thin & therefore light No chromatic aberration Disadvantages Design is more complex with more optical components LA Mission College Levine F2015 Bottom line • A reflector is usually the best choice for an amateur backyard telescope or a professional telescope. Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Let’s Practice Astronomers use large telescopes primarily because large telescopes A. have a bigger field of view B. have larger magnification C. gather more light D. None of the above Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Which of the following is an undesirable characteristic of a refracting telescope? A. Resolving power B. Harmonic convergence C. Chromatic aberration D. Atmospheric coherence Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 All other things being equal, you’ll buy the telescope with the ______________ that fits your budget and space/ weight limitations. A. Largest diameter primary mirror B. Largest diameter secondary mirror C. eyepiece with the largest magnification D. tube with the longest length Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 THE EFFECT OF THE ATMOSPHERE AND ENVIRONMENT Transmission of the Atmosphere • Astronomical observations from the ground are mostly constrained to visible light and radio wavelengths. • Near-infrared and submillimeter observations are also possible Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 The ideal site for an observatory Paranal Observatory (ESO), Chile • At high altitude -- stiller, drier air • • • • Good seeing Excellent Weather In the middle of nowhere Best ground-based sites include: Atacama Desert and Paranal in Chile, Mauna Kea in Hawaii, Antarctica Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 The ideal site for an observatory • • Altitude, weather, isolation.... From a high-flying aircraft or balloon! • • Kuiper Airborne observatory SOFIA Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 The ideal site for an observatory • • • Altitude, weather, isolation.... Space! No atmosphere. No weather. No neighbors! $$$ and usually very limited lifespan. Cosmic Rays • • Hubble Space Telescope Spitzer Space Telescope Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Let’s Practice You want to build an observatory that can study the ultraviolet emission from stars and galaxies. You should plan to locate it _____. A. on a high, dry desert plateau B. in space C. the site doesn’t matter much Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Most of the _____ light from astronomical objects reaches the surface of the Earth. A. Visible and Ultraviolet B. Infrared and Visible C. Visible and Radio D. Gamma Ray and Visible Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Which of the following wavelength ranges reaches the Earth from astronomical objects only in a few small windows and except for those windows requires a high flying aircraft, balloon or space-based telescope to make observations? A. Infrared B. Ultraviolet C. Radio D. X-ray Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Multiwavelength Astronomy Astronomy 1 — Elementary Astronomy LA Mission College Spring F2015 Astronomers observe across the Electromagnetic spectrum • • • • • • Gamma rays X-rays the ultraviolet (UV) visible light the infrared (IR) submillimeter & radio Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 WHAT WE LEARN ABOUT AT DIFFERENT WAVELENGTHS Infrared: More than Your Eyes Can See Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Xray & Gamma Ray Astronomy Compton Gamma Ray Observatory Image Credit: NASA • • • Hot objects & violent events matter heated to millions of degrees cosmic explosions, high speed collisions, material moving at extremely high speeds. • • • • • Black Holes Supernovae White dwarfs & pulsars Hottest part of Sun’s atmosphere observatories must be in space Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Infrared Astronomy • • Old, cold & dusty objects space based observatories or high-flying aircraft. • A few narrow bands from Earth • heat radiation from cool objects • penetrate thick interstellar dust • • • • • • star-forming regions central areas of our galaxy Cool stars Spitzer Space Telescope NASA/JPL-Caltech/R. Hurt (SSC) cold interstellar clouds star-forming galaxies planets Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Radio ( & Microwave) Astronomy Very Large Array (VLA) Image courtesy of NRAO/AUI • Very cold objects, traces atomic and molecular hydrogen • • • • Radiation left over from the Big Bang supernovae quasars interstellar gas and molecules Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 WRAP-UP Topic for Next Class • Solar System Overview Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Reading Assignment • • Astro: 5&7 Astropedia: 5 & 11 Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Homework • none yet Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015