Presentation on theme: "Chapter 4: Light. “ Ever since we crawled out of that primordial slime, that’s been our unifying cry, ’More light.’ Sunlight. Torchlight. Candlelight."— Presentation transcript:
“ Ever since we crawled out of that primordial slime, that’s been our unifying cry, ’More light.’ Sunlight. Torchlight. Candlelight. Neon, incandescent lights that banish the darkness from our caves to illuminate our roads, the insides of our refrigerators...Little tiny flashlights for those books we read under the covers when we’re suppose to be asleep. Light is more than watts... Light is metaphor. Light is knowledge. Light is life...” - Diane Frolov and Andrew Schneider Northern Exposure,1993
What can we learn by analyzing starlight? A star’s chemical composition A star’s temperature A star’s speed and direction of motion
How fast does light move? 186,000 miles per second! or 3 x 10 5 kilometers per second! Nothing travels faster than light!
Particle or Wave ? 1905, Einstein verified that light sometimes behaves as a wave and sometimes as particles. This is called the wave- particle duality of light!
Particle or Wave ? Wave: Electromagnetic wave Particles: Photons (packets of energy)
Units: 1 nanometer= 10 -9 meters! Different wavelengths correspond to different colors! Light as a Wave
The Doppler Shift Christian Doppler 1842: the observed frequency of an object is affected by its apparent motion Doppler shift occurs when the source of the waves is moving with respect to the observer occurs for all waves (e.g. water, sound, light)
Sound Waves low pitch low frequency long wavelength high pitch high frequency short wavelength The Doppler Shift
Light Waves A B constant wavelength detected by both A and B A detects longer wavelength redshift B detects shorter wavelength blueshift Stationary Star AB Star Moving to the Right
The Doppler Shift In Astronomy Spectrum of Stationary Source Spectrum of Approaching Source Spectrum of Receding Source 400nm 550nm 700nm
Detection of Extrasolar Planets: Stellar Wobble gravity of the planet causes the star to wobble back and forth 1990s, used Doppler effect to detect stellar wobbles
Concept Question If a star is moving away from us, which statement best describes what is happening to the star’s light? A) the light is blueshifted; we perceive that the wavelength increases B) the light is redshifted; we perceive that the wavelength increases C) the light is blueshifted; we perceive that the wavelength decreases D) the light is redshifted; we perceive that the wavelength decreases
What can we learn by analyzing starlight? A star’s chemical composition –by spectrum A star’s temperature –by color (peak wavelength) A star’s speed and direction of motion –by spectrum and Doppler Shift