Electromagnetic Spectrum

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Electromagnetic Spectrum

• Visible light and color
• Energy, frequency, wavelength
• A bit on telescopes
• Uses

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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 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)

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http//www.lcse.umn.edu/specs/labs/images/spectrum
.gif
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What is Light?

• Electric and magnetic fields waving
• Packets of energy called photons
• Energy and wavelength determine what the light
  can interact with

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http//www.yorku.ca/eye/spectrum.gif
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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

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High EnergyHigh FrequencyShort Wavelength
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High EnergyHigh FrequencyShort Wavelength

• Interacts with small things (cells, molecules,
  DNA)
• Created by high energy / hot processes

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http//upload.wikimedia.org/wikipedia/commons/9/99
/EM_Spectrum3-new.jpg
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?-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-g
amma-ray-lg.jpg
http//www.atnf.csiro.au/people/mdahlem/img/xmmtel
.gif
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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_1
95/1024/latest.html
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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.

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http//solarsystem.nasa.gov/deepimpact/images/Spec
t-Prism-sm.jpg
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http//wfc3.gsfc.nasa.gov/MARCONI/images-basic/spe
ctrum.jpg
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Why do our eyes see with Visible light?
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Atmospheric Windows
Wavelength, Energy
Frequency
High flying air planes or satellites
Need satellites to observe
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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

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Low EnergyLow FrequencyLong Wavelength
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Low EnergyLow FrequencyLong Wavelength

• Interact with larger things
• Lower energy processes

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http//upload.wikimedia.org/wikipedia/commons/9/99
/EM_Spectrum3-new.jpg
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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, HSTs successor)

http//upload.wikimedia.org/wikipedia/en/c/cf/Ir_g
irl.png
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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?id96170rendTypeId4
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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)

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Nancay Radio Telescope
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http//upload.wikimedia.org/wikipedia/commons/9/99
/EM_Spectrum3-new.jpg
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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/image06/060
123nebula.jpg
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Example The Sun

• http//sohowww.nascom.nasa.gov/data/realtime/realt
  ime-update.html
• Putting these together helps us understand the
  layers of our dynamic Sun.