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Electromagnetic Spectrum. Visible light and color Energy, frequency, wavelength A bit on telescopes Uses. Why do we care about light?. Everything we know in astronomy comes from light We only have physical samples from the Moon, Mars, and a couple comets Even these we study using light.
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Electromagnetic Spectrum • Visible light and color • Energy, frequency, wavelength • A bit on telescopes • Uses
Why do we care about light? • Everything we know in astronomy comes from light • We only have physical samples from the Moon, Mars, and a couple comets • Even these we study using light
Electromagnetic Radiation • Radiation: when things are sent out into empty space • EM radiation: light • Nuclear radiation: result of nuclear reactions, includes • Alpha particles (Helium nucleii) • Beta particles (positrons = anti-matter electrons) • Gamma “particles” (gamma EM radiation)
What is Light? • Electric and magnetic fields waving • Packets of energy called photons • Energy and wavelength determine what the light can interact with
False Color Images • Pictures attempt to “translate” invisible light to what we can see. • Representative color – colors have meaning, such as specific non-visible colors or chemicals • “Touch the Universe” by Noreen Grice
High EnergyHigh FrequencyShort Wavelength • Interacts with small things (cells, molecules, DNA) • Created by high energy / hot processes
http://upload.wikimedia.org/wikipedia/commons/9/99/EM_Spectrum3-new.jpghttp://upload.wikimedia.org/wikipedia/commons/9/99/EM_Spectrum3-new.jpg
ϒ-ray (gamma) and X-ray • High energy, short wavelengths • On Earth: radioactivity, some cancer treatment, broken bones, cavities • Astronomy: high energy processes, hot environments, colliding stars, around black holes, gas around galaxies, the Sun http://today.slac.stanford.edu/images/2007/swift-gamma-ray-lg.jpg http://www.atnf.csiro.au/people/mdahlem/img/xmmtel.gif
Ultraviolet (UV) • Slightly higher frequencies and shorter wavelengths than humans can see • Some birds and insects can see in the UV • On Earth: suntans, sunburn, cancer, can be used to sterilize equipment • Astronomy: Used to study the Sun and other hot objects • Hubble is mostly visible, but does have one UV instrument http://sohowww.nascom.nasa.gov/data/realtime/eit_195/1024/latest.html
Visible light and color • A small part of the total spectrum • Approximately 400-700nm, 4000-7000Å, violet to red • Each color the eye can see has a different wavelength.
http://solarsystem.nasa.gov/deepimpact/images/Spect-Prism-sm.jpghttp://solarsystem.nasa.gov/deepimpact/images/Spect-Prism-sm.jpg
Atmospheric Windows Wavelength, Energy Frequency High flying air planes or satellites Need satellites to observe
Why do our eyes see with Visible light? • Atmospheric windows • Visible and Radio get through an Earth-like atmosphere • Wavelength determines size of things it can interact with • Due to evolution, sizes of our eyes, sizes of molecules in our eyes, we see visible light
Low EnergyLow FrequencyLong Wavelength • Interact with larger things • Lower energy processes
http://upload.wikimedia.org/wikipedia/commons/9/99/EM_Spectrum3-new.jpghttp://upload.wikimedia.org/wikipedia/commons/9/99/EM_Spectrum3-new.jpg
Infrared (IR) • Slightly longer wavelength and lower frequency than the human eye can see. • Some animals including some snakes, some bats, and some insects can see IR. • On Earth: IR goggles help firefighters, soldiers, and home insulation experts; TV remote controls, Kinect • Astronomy: IR travels through dust so is good to look at young forming stars. (e.g., James Webb Space Telescope, HST’s successor) http://upload.wikimedia.org/wikipedia/en/c/cf/Ir_girl.png
Microwave/Sub-mm/Radio • Low energy, long wavelength • On Earth: microwave ovens, cellphone signals, radio for stereos, (formerly) TV broadcasts, GPS, walky-talkies, satellite communications, GPS, weather radar, radar guns • Astronomy: cool objects such as clouds of dust, gas clouds, entire galaxies, SETI, Cosmic Microwave Background (light from the Big Bang) http://apod.nasa.gov/apod/image/0302/sky_wmap_big.jpg http://cache.eb.com/eb/image?id=96170&rendTypeId=4
Bad Science: “Listening” to Radio Like all types of light, radio light is studied using either images or spectra (graphs of the “colors” – brightness at each wavelength)
http://upload.wikimedia.org/wikipedia/commons/9/99/EM_Spectrum3-new.jpghttp://upload.wikimedia.org/wikipedia/commons/9/99/EM_Spectrum3-new.jpg
Each part of the wavelength tells us part of the story.Must put together all wavelengths to get the full story. http://www.thunderbolts.info/tpod/2006/image06/060123nebula.jpg
Example: The Sun • http://sohowww.nascom.nasa.gov/data/realtime/realtime-update.html • Putting these together helps us understand the layers of our dynamic Sun.