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

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

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 Frequency

Short Wavelength

High EnergyHigh Frequency

Short 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.jpg

ϒ-ray (gamma) and X-ray

http://today.slac.stanford.edu/images/2007/swift-gamma-ray-lg.jpg

http://www.atnf.csiro.au/people/mdahlem/img/xmmtel.gif

• 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

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 instrumenthttp://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.jpg

Why do our eyes see with Visible light?

Atmospheric Windows

Need satellites to observe

Wavelength, Energy

Frequency

High flying air planes or satellites

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 Frequency

Long Wavelength

Low EnergyLow Frequency

Long Wavelength

• Interact with larger things

• Lower energy processes

http://upload.wikimedia.org/wikipedia/commons/9/99/EM_Spectrum3-new.jpg

Infrared (IR)

http://upload.wikimedia.org/wikipedia/en/c/cf/Ir_girl.png

• 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)

Microwave/Sub-mm/Radio

http://apod.nasa.gov/apod/image/0302/sky_wmap_big.jpg

• 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://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)

Nancay Radio Telescope

http://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.