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
Announcements
Last Class History Galileo, Newton (right?) Gravity & Tides Intro to light LT EM Spectrum
This Class LT EM Spectrum Telescopes & Observatories Light and the Atmosphere Multi-wavelength Astronomy
Electromagnetic Spectrum Astronomy 1 Elementary Astronomy LA Mission College Spring F2015
The Electromagnetic Spectrum All these are the same thing as visible light Gamma rays -- highest frequency, shortest wavelength, greatest energy per photon Radio waves -- lowest frequency, longest wavelength, least energy per photon
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.
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.
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)
Consider Xrays with frequency 10 17 Hz. Light with a frequency one millionth of this (i.e. 10 11 Hz) is most likely to be. A. Ultraviolet B. Gamma Ray C. Microwave
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.
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 characterized by size, shape, speed,specific amount of energy, mass, etc. particles do not display interference key property is the photoelectric effect
The Original Double-slit Experiment
Particles Waving
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 photoelectric effect The particle of light or quantum of light is called a photon Particle behavior
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
TELESCOPES
What do you think? Why do Astronomers use Telescopes?
Why do Astronomers Use Telescopes? To gather the faint light from distant objects The bigger the telescope, the more light it gathers This is the most important property of a telescope! To resolve details of these objects 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
There are two main types of telescopes Refractors Think Pirate s Spyglass Galileo s Telescopes were Refractors Refractors have a large lens or lenses, normally at the front of the telescope, which are the primary optical component
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
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
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
Refractors vs. Reflectors Refractors Advantages Rugged Sealed Tube Relatively Simple design Disadvantages Chromatic Aberration Heavy Difficult to make glass optically perfect 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
Bottom line A reflector is usually the best choice for an amateur backyard telescope or a professional telescope.
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
Which of the following is an undesirable characteristic of a refracting telescope? A. Resolving power B. Harmonic convergence C. Chromatic aberration D. Atmospheric coherence
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
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
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
The ideal site for an observatory Altitude, weather, isolation... From a high-flying aircraft or balloon! Kuiper Airborne observatory SOFIA
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
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
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
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
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
WHAT WE LEARN ABOUT AT DIFFERENT WAVELENGTHS
Infrared: More than Your Eyes Can See
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
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
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
WRAP-UP
Topic for Next Class Solar System Overview
Reading Assignment Astro: 5&7 Astropedia: 5 & 11
Homework none yet