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# EM Waves

TermDefinition
Reflecting Telescope light captured by a curved mirror
Radio Telescope Light captured by a curved metal mirror
Refracting Telescope Light captured by a curved glass lens
Telescopes a telescope is a device for collecting and bringing to a detector (eye/camera) electromagnetic (EM) radiation - eg. light. EM source-Telescope-Detector-Flux data on EM source
James Clerk Maxwell Proved rings of Saturn had to be made of small particles. Developed electromagnetic theory of light
Electromagnetic Theory of Light An electromagnetic wave is a disturbance propagated as a variation in the local electric and magnetic fields at the speed of light
Wave A travelling disturbance. Any form of change or disturbance that propagates from one region to another can be thought of as a wave.
Frequency (f) Number of waves crests passing per second
Wavelength (lambda) Diagram 1
speed = Wavelength(lambda) x frequency(f)
Speed of Light c = 3 x 10^8 m/s
C = lambda x f OOTETK (units: wavelength in meters, frequency in Hertz)
Starlight How stars tell us about themselves
Collecting the Message Telescope
The Doppler Effect defined Christian Doppler noted an apparent change in the observed wavelength of a signal (sound wave) as a result of motion either towards or away from an observer.
The Doppler Effect applied Applies to all wave-like phenomena. Pitch increases as vehicle approaches and decreases as it moves away- the change is an apparent change - not a change in the siren's actual tone
Doppler Diagram D2 and D3
Doppler Interpretation wavelength observed < wavelength if motion of source is towards observer. While wavelength observed > wavelength if motion of source is away from observer.
Dopplers Formula (lamdaobs - lambda)/Lamda = V/c. -V means motion towards and +V if motion is away.
Motion Towards Observer Shorter wavelength observed (blue shifted)lambdaobs - lambda
Motion Away from Observer Longer wavelength observed (red shifted)
Proper Motion The measured angular shift on the sky in arcseconds per year
Hubbles Law There is a systematic increase in the velocity of recession of a galaxy with increasing distance
Hubbles Law equation OOTETK Vgalaxy = H x Dgalaxy (where H is hubbles constant)
Important point about waves They transmit information in the form of energy
Energy A measure of the ability to do work. Units are Joules(J)
Electromagnetic Spectrum Longest wavelengths are radio waves and shortest wavelengths are gamma rays.
Radiant Energy The amount of energy E carried by an electromagnetic wave is related to its frequency. So, the greater the frequency the greater the amount of energy carried by the wave.
Energy Formula OOTETK E = h x f (where h= Planck's constant)
Velocity formula Velocity = distance
Stellar Spectra Stars radiate most of their EM radiation at UV, visual and IR wavelengths. Absorption lines can be used to study stellar motion
Luminosity(L) Total amount of EM energy radiated to all wavelengths into space per second. Units=Joules/seconds=Watts
Flux(F) Energy received per square meter per second. units=Watts/m2
Flux, luminosity and distance equation OOTETK F=L/(4pie x d^2)
Different Wavelength Telescopes Radio, Microwave/infared, visible, UV/Xray
Radio 1 Radar studies of planets, magnetic fields, interstellar gas, galactic structure, active galaxies
Microwave, Infared 2 Star formation, interstellar dust, cool stars, galactic structure
Visible 3 Planets, stars, galactic structure, galaxy distribution
UV, X-Ray 4 Hot interstellar medium, active galactic nuclei
Created by: davidvachon1