# Electromagnetic Spectrum

STORIES IN THE WAVES Exploring the Electromagnetic Spectrum (with a Gravitational Wave Bonus) The next slides show images of the SAME region of sky, but using different types of light The view in VISIBLE LIGHT INFRARED

RADIO WAVES RADIO WAVES GAMMA RAYS Different types of light give us different information! But what IS light?

Its ELECTROMAGNETIC RADIATION Normally we think of visible light, but there are lots of types of light that are all produced by accelerating charged particles (basically wiggling). Electromagnetic radiation This wiggling creates a changing ELECTRIC FIELD and MAGNETIC FIELD

The resulting electromagnetic wave propagates through space Electromagnetic Radiation Oscillating waves have certain properties: Wavelength (l) the length over which the wave repeats in pattern (meters). Frequency (f) how often the wave repeats itself (cycles per second). Speed = wavelength x frequency. For light in a vacuum, this speed is constant (c = lf = 3 x 108 m/s).

l Frequency 6457312 l 10 20 19 18 17

16 15 14 13 12 11 546738912 Light as a Particle Light can also behave like a particle. We call the particlelike aspect of light a photon. The ENERGY of a photon is INVERSELY PROPORTIONAL to

its wavelength and DIRECTLY PROPORTIONAL to its frequency. E = hc/l where, h = Plancks constant (6.626 x 1034 Js) c = Speed of light (3 x 108 m/s) E = hf A RED photon has a _____ wavelength, _____ frequency and _____ energy than a

BLUE photon. A. B. C. D. E. F. G. H. longer, higher, greater

longer, higher, smaller longer, lower, greater longer, lower, smaller shorter, higher, greater shorter, higher, smaller shorter, lower, greater shorter, lower, smaller Electromagnetic SpectrumWavelength (m) 3x104

3 3x10-4 3x10-8 Radio waves 60 Hz 102

106 Ultraviolet Visible light Infrared 3x10-12 Gamma rays

X-rays F TV M TV Ch 2Ch 7& up 6 108 1010

1012 1014 l = 7.5x10-7 m f = 4.0x1014 Hz 1016 1018

l = 4.0x10-7 m f = 7.5x1014 Hz Visible Light 1020 Frequency (Hz)

Which of the following types of electromagnetic radiation travels fastest in a vacuum? A. B. C. D. E. F. Gamma rays

Infrared Radio Ultraviolet X-rays They all travel at the same speed RADIO WAVES Used for communication Long wavelengths; low energy. Heres the irregular galaxy Centaurus A as it appears VISIBLY

(left) and a composite VISIBLE + RADIO WAVES (right) Image credit; https://svs.gsfc.nasa.gov/10770 MICROWAVES Used to cook and for cell phones. Mostly harmless unless specific frequency. Higher energy/shorter wavelength than radio waves. http:// www.esa.int/Our_Activities/Space_Science/Planck/Planck_a nd_the_cosmic_microwave_background

INFRARED LIGHT Sometimes called heat waves you can feel, but not see, this light. What a black cat looks like in infrared wavelengths. VERY different information! Which parts of the

cat are cool? Warm? Image credit: http:// coolcosmos.ipac.caltech.edu/image_galleries/ir_zoo/cat.html More Than the Eyes Can See The Universe in IR http://coolcosmos.ipac.caltech.edu/videos/ more_than_your/ VISIBLE LIGHT

Detected by your eyes. Orion VISIBLY (left) and in the INFRARED (right). See how much were missing out on? Image credit: https:// www.nasa.gov/mission_pages/SOFIA/status_update_10-46F.html WHAT YOU CAN SEE AINT MUCH The Visible Inch http://www.youtube.com/watch?v=kfS5Qn0wn2o ULTRAVIOLET LIGHT

Energetic enough to cause sunburns! Heres the Sun visibly (left) and in the UV (right) Images from: https://earthobservatory.nasa.gov/images/37575 X-RAYS Very short wavelengths, high energies. Penetrates human tissue. Reveals extremely HOT and VIOLENT regions in the universe Image from: https://imagine.gsfc.nasa.gov/educators/lessons/supernova/

GAMMA RAYS Most energetic; shortest wavelength; go THROUGH just about everything. Crab Nebula/supernova remnant on the left; gamma ray burster on the right. GIF from: https:// DISCUSSION QUESTION: When the black holes collided to create the event we observed as GW150914, the amount of energy released exceeded the rest of the

observable universe combined. BUT NO ELECTROMAGNETIC RADIATION WAS DETECTED FROM IT. Why not? The gravitational wave event GW170817 coincided with this optical observation: Figure 1 from The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. I. Discovery of the Optical Counterpart Using the Dark Energy Camera, by M. Soares-Santos et al 2017 ApJL 848 L16

The optical event was determined to have occurred in a galaxy 144 million light years away. IR and UV detections were also made. In addition, a short burst of gamma rays was detected within 2 seconds of the gravitational wave detection. What does this information tell you about the objects that merged to create GW 170817? What does this information tell you about the speed of gravitational waves compared to the speed of

electromagnetic waves?

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